Parsing/RPN calculator algorithm: Difference between revisions
add FreeBASIC
(Added solution for Action!) |
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25 + XEQ 1: 3.000122
Result is... 3.000122</pre>
=={{header|FreeBASIC}}==
<lang freebasic>#define NULL 0
type node
'implement the stack as a linked list
n as double
p as node ptr
end type
function spctok( byref s as string ) as string
'returns everything in the string up to the first space
'modifies the original string to begin at the fist non-space char after the first space
dim as string r
dim as double i = 1
while mid(s,i,1)<>" " and i<=len(s)
r += mid(s,i,1)
i+=1
wend
do
i+=1
loop until mid(s,i,1)<>" " or i >= len(s)
s = right(s,len(s)-i+1)
return r
end function
sub print_stack( byval S as node ptr )
'display everything on the stack
print "Stack <--- ";
while S->p <> NULL
S = S->p
print S->n;" ";
wend
print
end sub
sub push( byval S as node ptr, v as double )
'push a value onto the stack
dim as node ptr x
x = allocate(sizeof(node))
x->n = v
x->p = S->p
S->p = x
end sub
function pop( byval S as node ptr ) as double
'pop a value from the stack
if s->P = NULL then return -99999
dim as double r = S->p->n
dim as node ptr junk = S->p
S->p = S->p->p
deallocate(junk)
return r
end function
dim as string s = "3 4 2 * 1 5 - 2 3 ^ ^ / +", c
dim as node StackHead
while len(s) > 0
c = spctok(s)
print "Token: ";c;" ";
select case c
case "+"
push(@StackHead, pop(@StackHead) + pop(@StackHead))
print "Operation + ";
case "-"
push(@StackHead, -(pop(@StackHead) - pop(@StackHead)))
print "Operation - ";
case "/"
push(@StackHead, 1./(pop(@StackHead) / pop(@StackHead)))
print "Operation / ";
case "*"
push(@StackHead, pop(@StackHead) * pop(@StackHead))
print "Operation * ";
case "^"
push(@StackHead, pop(@StackHead) ^ pop(@StackHead))
print "Operation ^ ";
case else
push(@StackHead, val(c))
print "Operation push ";
end select
print_stack(@StackHead)
wend</lang>
{{out}}<pre>
Token: 3 Operation push Stack <--- 3
Token: 4 Operation push Stack <--- 4 3
Token: 2 Operation push Stack <--- 2 4 3
Token: * Operation * Stack <--- 8 3
Token: 1 Operation push Stack <--- 1 8 3
Token: 5 Operation push Stack <--- 5 1 8 3
Token: - Operation - Stack <--- -4 8 3
Token: 2 Operation push Stack <--- 2 -4 8 3
Token: 3 Operation push Stack <--- 3 2 -4 8 3
Token: ^ Operation ^ Stack <--- 8 -4 8 3
Token: ^ Operation ^ Stack <--- 65536 8 3
Token: / Operation / Stack <--- 0.0001220703125 3
Token: + Operation + Stack <--- 3.0001220703125
</pre>
=={{header|FunL}}==
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