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Array: Difference between revisions
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The lower bound of non-associative arrays in many [[:Category:Programming Languages|programming languages]] is commonly fixed at either 0 ([[C]] and relatives) or 1 (Old [[Fortran]] and relatives); or an arbitrary integer ([[Pascal]] and relatives, modern Fortran). In [[Ada]] any discrete type can used as an index. Zero-based indexing is best thought of in terms of the index being an offset from the beginning of the array. Thus the first element is located zero elements from this starting point. The alternative can be thought of as ordinal indexes referring to the first, second, ... and ''n''th elements of the array.
In most programming languages, arrays are accessed by using the array brackets <
==[[C]]==
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same task, open a text file and compute letter frequency
<lang ocaml>let () =
let ic = open_in Sys.argv.(1) in
let base = int_of_char 'a' in
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for i=0 to 25 do
Printf.printf "%c -> %d\n" (char_of_int(i + base)) arr.(i)
done</
Here is [http://caml.inria.fr/pub/docs/manual-ocaml/libref/Array.html the documentation] of the module Array. (there is also a [http://caml.inria.fr/pub/docs/manual-ocaml/libref/Bigarray.html Bigarray module])
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=={{header|Pascal}}==
This defines an array suitable to hold a 64x64 truecolor image (i.e. red, green and blue RGB values all can go from 0 to 255) and then sets the color of a single pixel
<lang pascal>
type
color = red, green, blue;
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picture[4, 7, blue] := 0
end.
</
=={{header|Python}}==
Example: open a text file and compute letter frequency.
<lang python>
import string
if hasattr(string, ''ascii_lowercase''):
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print "%s=%d" % (chr(i + ord('a'), lettercounts[i]),
</
This example defines the function and provides a sample usage. The ''if ... __main__...'' line allows it to be cleanly imported into any other Python code while also allowing it to function as a standalone script. (A very common Python idiom).
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Using a numerically indexed array (list) for this is artificial and clutters the code somewhat. The more Pythonic approach would be:
<lang python>
...
def countletters(file_handle):
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results[c] = results.get(c,0) + 1
return results
</
Which eliminates the ungainly fiddling with ordinal values and offsets. More importantly it allows the results to be more simply printed using:
<lang python>
lettercounts = countletters(sourcedata)
for letter,count in lettercounts.items():
print "%s=%s" % (letter, count),
</
Again eliminating all fussing with the details of converting letters into list indices.
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