Control Structures: Difference between revisions
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[[Category:Encyclopedia]]'''Control structures''' are features of programming languages that influence the code flow. Examples of control structures are: |
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{{task}} |
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*loops, which repeat sections of code |
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*conditions, which selectively execute sections of code |
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*exceptions, which help in error handling and avoid causing more problems when there is another problem |
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*jumps (a.k.a. "branches" or "gotos"), which explicitly and usually unconditionally set the next instruction to be executed by the program |
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Examples of these structures can be found on the following pages: |
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Control structures are features of programming languages that influence the code flow. Two common examples are loops and conditions. The task here is to demonstrate control structures supported by different programming languages. |
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* [[Conditional Structures]] |
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* [[Flow Control Structures]] |
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* [[Loop Structures]] |
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These control structures depend on conditions to control their behavior. |
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* [[Exceptions]] |
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* [[Help:Orphaned code]] |
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==[[AppleScript]]== |
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[[Category:AppleScript]] |
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===if-then-else=== |
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if myVar is "ok" then return true |
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set i to 0 |
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if i is 0 then |
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return "zero" |
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else if i mod 2 is 0 then |
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return "even" |
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else |
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return "odd" |
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end if |
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===repeat-until=== |
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set i to 5 |
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repeat until i is less than 0 |
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set i to i - 1 |
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end repeat |
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repeat |
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--endless loop |
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end repeat |
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==[[C]]== |
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[[Category:C]] |
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===if-then-else=== |
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'''Compiler:''' [[GCC]] 4.1.2 |
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int main (int argc, char ** argv) { |
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int input = 2; |
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if ( 3 == input ) { |
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// Do something |
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} |
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if ( 3 == input ) { |
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// Do something |
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} else { |
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// Do something else |
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} |
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} |
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===switch=== |
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'''Compiler:''' [[GCC]] 4.1.2 |
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int main (int argc, char ** argv) { |
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int input = 42; |
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switch (input) { |
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case 0: |
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// Do something, because input = 0 |
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break; |
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case 1: |
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// Do something, because input = 1 |
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break; |
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case 2: |
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// Do something, because input = 2 |
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default: |
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// Do something else. |
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break; // Optional |
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} |
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} |
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===while=== |
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'''Compiler:''' [[GCC]] 4.1.2 |
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int main (int argc, char ** argv) { |
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int condition = 1; |
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while ( condition ) { |
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// Do something |
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// Don't forget to change the value of condition. |
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// If it remains nonzero, we'll have an infinite loop. |
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} |
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} |
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===do-while=== |
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'''Compiler:''' [[GCC]] 4.1.2 |
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int main (void) { |
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int condition = 1; |
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do { |
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// Do something |
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// Don't forget to change the value of condition. |
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// If it remains nonzero, we'll have an infinite loop. |
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} while ( condition ); |
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} |
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==[[C plus plus|C++]]== |
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[[Category:C plus plus]] |
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=== Run-Time Control Structures === |
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==== for ==== |
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'''Compiler:''' [[GCC]] 3.3.4 |
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#include <iostream> |
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int main() |
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{ |
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int i = 1; |
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// Loops forever: |
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for(; i == 1;) |
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std::cout << "Hello, World!\n"; |
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} |
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==== goto ==== |
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'''Compiler:''' [[GCC]] 3.3.4 |
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#include <iostream> |
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int main() |
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{ |
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LOOP: |
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std::cout << "Hello, World!\n"; |
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goto LOOP; |
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} |
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Note that this may also be used in conjunction with other forms of branching. |
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====if-then-else==== |
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'''Compiler:''' [[GCC]] 4.1.2 |
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int main (void) { |
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int input = 2; |
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if ( 3 == input ) { |
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// Do something |
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} |
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if ( 3 == input ) { |
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// Do something |
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} else { |
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// Do something else |
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} |
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} |
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====switch==== |
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'''Compiler:''' [[GCC]] 4.1.2 |
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int main (void) { |
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int input = 42; |
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switch (input) { |
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case 0: |
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// Do something, because input = 0 |
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break; |
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case 1: |
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// Do something, because input = 1 |
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break; |
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case 2: |
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// Do something, because input = 2 |
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default: |
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// Do something else. |
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break; // Optional |
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} |
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} |
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====while==== |
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'''Compiler:''' [[GCC]] 4.1.2 |
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int main (void) { |
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int condition = 1; |
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while ( condition ) { |
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// Do something |
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// Don't forget to change the value of condition. |
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// If it remains nonzero, we'll have an infinite loop. |
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} |
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} |
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====do-while==== |
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'''Compiler:''' [[GCC]] 4.1.2 |
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int main (void) { |
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int condition = 1; |
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do { |
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// Do something |
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// Don't forget to change the value of condition. |
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// If it remains nonzero, we'll have an infinite loop. |
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} while ( condition ); |
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} |
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=== Compile-Time Control Structures === |
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==== Preprocessor Techniques ==== |
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#ifdef, #ifndef, etc.. |
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==== Template Metaprogramming Techniques ==== |
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Template metaprogramming techniques. |
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==[[ColdFusion]]== |
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[[Category:ColdFusion]] |
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===if-elseif-else=== |
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'''Compiler:''' [[ColdFusion]] any version |
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<cfif x eq 3> |
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do something |
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<cfelseif x eq 4> |
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do something else |
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<cfelse> |
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do something else |
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</cfif> |
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===switch=== |
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'''Compiler:''' [[ColdFusion]] any version |
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<cfswitch expression="#x#"> |
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<cfcase value="1"> |
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do something |
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</cfcase> |
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<cfcase value="2"> |
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do something |
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</cfcase> |
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<cfdefaultcase> |
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do something |
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</cfdefaultcase> |
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</cfswitch> |
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==[[OCaml]]== |
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[[Category:OCaml]] |
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===if-then-else=== |
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'''Compiler:''' [[OCaml]] 3.09 |
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let condition = true |
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if condition then |
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()//do something |
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else |
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()//do something else |
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===match-with=== |
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match expression with |
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| 0 -> ()//do something |
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| 1 -> ()//do something |
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| n when n mod 2 = 0 -> ()//do something |
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| _ -> ()//do something |
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==[[Pascal]]== |
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[[Category:Pascal]] |
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===if-then-else=== |
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'''Compiler:''' [[Turbo Pascal]] 7.0 |
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IF condition1 THEN |
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procedure1 |
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ELSE |
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procedure3; |
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IF condition1 THEN |
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BEGIN |
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procedure1; |
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procedure2; |
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END |
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ELSE |
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procedure3; |
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IF condition 1 THEN |
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BEGIN |
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procedure1; |
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procedure2; |
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END |
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ELSE |
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BEGIN |
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procedure3; |
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procedure4; |
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END; |
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===while=== |
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'''Compiler:''' [[Turbo Pascal]] 7.0 |
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WHILE condition1 DO |
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BEGIN |
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procedure1; |
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procedure2; |
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END; |
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===do-while=== |
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'''Compiler:''' [[Turbo Pascal]] 7.0 |
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DO |
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BEGIN |
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procedure1; |
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procedure2; |
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END |
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WHILE condition1; |
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===for=== |
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'''Compiler:''' [[Turbo Pascal]] 7.0 |
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FOR counter=1 TO 10 DO |
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BEGIN |
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procedure1; |
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procedure2; |
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END; |
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==[[Perl]]== |
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[[Category:Perl]] |
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===if-then-else=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 0; |
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my $condition2 = 1; |
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if ( $condition1 ) { |
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# Do something |
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} |
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# post-conditional if |
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do_something() if $condition1; |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 0; |
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my $condition2 = 1; |
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if ( $condition1 ) { |
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# Do something |
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} elsif ( $condition2 ) { |
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# Do somethine else |
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} |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 0; |
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my $condition2 = 1; |
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if ( $condition1 ) { |
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# Do something |
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} else { |
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# Do something else |
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} |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 0; |
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my $condition2 = 1; |
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if ( $condition1 ) { |
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# Do something |
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} elsif ( $condition2 ) { |
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# Do something else |
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} else { |
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# Do that other thing |
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} |
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($condition) ? print "Then\n" : print "Else\n"; |
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# or |
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my $var = ($condition) ? "Then" : "Else"; |
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===unless=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 0; |
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unless ( $condition1 ) { |
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# Do something |
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} |
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# post-conditional unless |
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do_something() unless $condition1; |
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unless ( $condition1 ) { |
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# Do something |
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} else { |
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# Do something else |
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} |
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===while=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 0; |
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while ( $condition1 ) { |
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# Do something. |
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# Remember to change the value of condition1 at some point. |
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} |
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===do-while=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 0; |
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do { |
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# Do something. |
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# Remember to change the value of condition1 at some point. |
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} while ( $condition1 ); |
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===until=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 1; |
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until ( $condition1 ) { |
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# Do something. |
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# Remember to change the value of condition1 at some point. |
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} |
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===do-until=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my $condition1 = 1; |
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do { |
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# Do something. |
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# Remember to change the value of condition1 at some point. |
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} until ( $condition1 ); |
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===switch=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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use Switch; |
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$input = 42; |
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switch ($input) { |
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case 0 { |
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# Do something, because input = 0 |
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} |
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case 1 { |
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# Do something, because input = 1 |
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} |
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case "coffee" { |
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# Do something, because input = coffee |
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} |
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else { |
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# Do something else. |
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} |
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} |
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===goto=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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Typically dispised by most Perl programmers |
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goto LABELB; |
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LABELA: # note labels end with a colon not semi-colon |
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goto END; |
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LABELB: |
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goto LABELA; |
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END: |
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exit(0); |
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==[[Python]]== |
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[[Category:Python]] |
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===if-then-else=== |
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if x == 0: |
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foo() |
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elif x == 1: |
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bar() |
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elif x == 2: |
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baz() |
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else: |
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boz() |
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===while=== |
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while ok(): |
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foo() |
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bar() |
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baz() |
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else: |
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# break was not called |
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quux() |
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===for=== |
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for i in range(10): |
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print i |
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else: |
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# break was not called |
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foo() |
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===try-except-finally-else=== |
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'''Interpreter''': Python 2.5 |
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Before Python 2.5 it was not possible to use finally and except together. |
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try: |
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foo() |
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except TypeError: |
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bar() |
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finally: |
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baz() |
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else: |
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# no exception occurred |
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quux() |
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===with=== |
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'''Interpreter''': Python 2.5 |
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foo could for example open a file or create a lock or a database transaction: |
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with foo() as bar: |
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baz(bar) |
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==[[PHP]]== |
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[[Category:PHP]] |
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===if-then-else=== |
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if ($x == 0) { |
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foo(); |
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} else if ($x == 1) { |
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bar(); |
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} else if ($x == 2) { |
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baz(); |
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} else { |
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boz(); |
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} |
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===while=== |
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while(ok()) { |
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foo(); |
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bar(); |
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baz(); |
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} |
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===for=== |
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for($i = 0; $i < 10; ++$i) { |
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echo $i; |
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} |
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===foreach=== |
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foreach(range(0, 9) as $i) { |
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echo $i; |
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} |
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===switch=== |
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switch($c) |
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{ |
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case 'a': |
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foo(); |
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break; |
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case 'b': |
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bar(); |
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default: |
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foobar(); |
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} |
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==[[Ruby]]== |
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[[Category:Ruby]] |
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===if-then-else=== |
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if s == 'Hello World' |
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foo |
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elsif s == 'Bye World' |
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bar |
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else |
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deus_ex |
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end |
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===while=== |
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while true do |
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foo |
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end |
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===for=== |
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for i in [0..4] do |
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foo |
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end |
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===case-when-else=== |
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case cartoon_character |
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when 'Tom' |
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chase |
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when 'Jerry' |
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flee |
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else |
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nil |
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end |
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===ternary=== |
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s == 'Hello World' ? foo : bar |
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==[[Java]]== |
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[{Category:Java]] |
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===if-then-else=== |
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if(s.equals("Hello World")) |
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{ |
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foo(); |
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} |
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else if(s.equals("Bye World")) |
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{ |
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bar(); |
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} |
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else |
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{ |
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deusEx(); |
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} |
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===while=== |
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while(true) |
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{ |
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foo(); |
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} |
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===for=== |
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for(int i = 0; i < 5; i++) |
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{ |
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foo(); |
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} |
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===ternary=== |
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s.equals("Hello World") ? foo : bar |
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===switch=== |
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switch(c) { |
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case 'a': |
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foo(); |
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break; |
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case 'b': |
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bar(); |
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default: |
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foobar(); |
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} |
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==[[JavaScript]]== |
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[[Category:JavaScript]] |
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===if-then-else=== |
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if(s=="Hello World") |
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{ |
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foo(); |
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} |
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else if(s=="Bye World") |
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{ |
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bar(); |
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} |
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else |
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{ |
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deusEx(); |
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} |
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===while=== |
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while(true) |
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{ |
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foo(); |
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} |
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===for=== |
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for(var i = 0; i < 5; i++) |
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{ |
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foo(); |
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} |
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==[[Smalltalk]]== |
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[[Category:SmallTalk]] |
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"Conditionals in Smalltalk are really messages sent to Boolean objects" |
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(( balance) > 0) |
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ifTrue: [Transcript cr; show: 'still sitting pretty!'.] |
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ifFalse: [Transcript cr; show: 'No money till payday!'.]. |
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=Iterative= |
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These control structure operate on datasets. |
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==[[AppleScript]]== |
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[[Category:AppleScript]] |
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===repeat-with=== |
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repeat with i from 1 to 20 |
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--do something |
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end repeat |
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set array to {1,2,3,4,5} |
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repeat with i in array |
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display dialog i |
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end repeat |
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==[[C plus plus|C++]]== |
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[[Category:C plus plus]] |
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===for_each === |
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'''Compiler:''' [[GCC]] 4.1.1 |
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#include <iostream> // std::cout, std::endl |
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#include <vector> // std::vector |
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#include <algorithm> // std::for_each |
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struct sum |
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{ |
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int _sum; |
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sum() : _sum(0) {}; // Initialize sum with 0; |
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void operator() (int a) { _sum += a; } // this function will be called for every element |
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}; |
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int main() |
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{ |
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std::vector<int> v; |
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v.push_back(10); |
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v.push_back(23); |
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v.push_back(34); |
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/* Note that for_each gets a fresh instance of sum passed, |
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* applies every element beginning with *v.begin() up to, |
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* but not including v.end() to the function object |
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* and returns a copy of it. |
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*/ |
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sum the_sum = std::for_each(v.begin(), v.end(), sum()); |
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std::cout << "The sum is " << the_sum._sum << std::endl; |
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return 0; |
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} |
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==[[Java]]== |
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[[Category:Java]] |
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===foreach=== |
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'''Platform:''' [[J2SE]] 1.5.0 |
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Object[] objects; |
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// ... |
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for (Object current : objects[]) { |
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// ... |
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} |
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int[] numbers; |
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// ... |
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for (int i : numbers) { |
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// ... |
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} |
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==[[Perl]]== |
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[[Category:Perl]] |
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===for=== |
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'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my $limit = 5; |
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for ( my $iterator = 0; $iterator < $limit; $iterator++ ) { |
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# Do something |
|||
} |
|||
# for-variant, implicit iteration |
|||
for (0..$limit) { |
|||
# Do something |
|||
} |
|||
do_something() for 0..$limit; |
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===foreach=== |
|||
'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my @numbers = (1, 2, 3); |
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my %names = (first => "George", last => "Jetson"); |
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foreach my $number (@numbers) { |
|||
# Do something with $number |
|||
} |
|||
foreach my $key (keys %names) { |
|||
# Do something with $key (values are accessible as %names{$key} ) |
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} |
|||
===map=== |
|||
'''Interpreter:''' [[Perl]] 5.8.8 |
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#!/usr/bin/perl -w |
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use strict; |
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my @numbers = (1, 2, 3); |
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my @target; |
|||
@target = map { |
|||
# Do something with $_ |
|||
} @numbers; |
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@target = map($_ + 1, @numbers); |
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sub a_sub { |
|||
# Do something with $_ |
|||
} |
|||
@target = map a_sub @numbers; |
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===grep=== |
|||
'''Interpreter:''' [[Perl]] 5.8.8 |
|||
#!/usr/bin/perl -w |
|||
use strict; |
|||
my @people = qw/Bobbie Charlie Susan/; |
|||
my @target; |
|||
@target = grep { |
|||
# Discriminate based on $_ |
|||
} @people; |
|||
# Feed grep into map, this picks out elements 1, 3, 5, etc. |
|||
@target = map($people[$_], grep($_ & 1, 0..$#people)); |
|||
# Pick out the diminutive names |
|||
@target = grep(/ie$/, @people); |
|||
sub a_sub { |
|||
# Do something with $_, and return a true or false value |
|||
} |
|||
@target = grep a_sub @people; |
|||
==[[Python]]== |
|||
[[Category:Python]] |
|||
=== for === |
|||
for x in ["foo", "bar", "baz"]: |
|||
print x |
|||
==[[Ruby]]== |
|||
[[Category:Ruby]] |
|||
=== each === |
|||
['foo', 'bar', 'baz'].each do |x| |
|||
puts x |
|||
end |
|||
=== collect === |
|||
array = ['foo', 'bar', 'baz'].collect do |x| |
|||
foo x |
|||
end |
|||
=== map === |
|||
array = ['foo', 'bar', 'baz'].map {|x| foo x } |
|||
=== inject === |
|||
string = ['foo', 'bar', 'baz'].inject("") do |s,x| |
|||
s << x |
|||
s |
|||
end |
|||
sum = ['foo', 'bar', 'baz'].inject(0) do |s,x| |
|||
s + x.size |
|||
s |
|||
end |
|||
product = ['foo', 'bar', 'baz'].inject(1) do |p,x| |
|||
p * x.size |
|||
p |
|||
end |
|||
hash = ['foo', 'bar', 'baz'].inject({}) do |h,x| |
|||
h[x] = x.size |
|||
h |
|||
end |
|||
boolean = ['foo', 'bar', 'baz'].inject(true) do |b,x| |
|||
b &&= x != 'bar' |
|||
b |
|||
end |
|||
==[[Tcl]]== |
|||
[[Catgory:Tcl]] |
|||
=== foreach === |
|||
foreach i {foo bar baz} { |
|||
puts "$i" |
|||
} |
|||
==[[UNIX Shell]]== |
|||
[[Category:UNIX Shell]] |
|||
===for=== |
|||
'''Interpreter:''' [[Bourne Again SHell]] |
|||
#!/bin/bash |
|||
ARRAY="VALUE1 VALUE2 VALUE3 VALUE4 VALUE5" |
|||
for ELEMENT in $ARRAY |
|||
do |
|||
echo $ELEMENT # Print $ELEMENT |
|||
done |
|||
'''Interpreter:''' [[Debian Almquist SHell]] |
|||
#!/bin/sh |
|||
ARRAY="VALUE1 VALUE2 VALUE3 VALUE4 VALUE5" |
|||
for ELEMENT in $ARRAY |
|||
do |
|||
echo $ELEMENT # Print $ELEMENT |
|||
done |
Latest revision as of 20:37, 22 October 2008
Control structures are features of programming languages that influence the code flow. Examples of control structures are:
- loops, which repeat sections of code
- conditions, which selectively execute sections of code
- exceptions, which help in error handling and avoid causing more problems when there is another problem
- jumps (a.k.a. "branches" or "gotos"), which explicitly and usually unconditionally set the next instruction to be executed by the program
Examples of these structures can be found on the following pages: