Simple infix expression evaluation using a stack.
Python, 37 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | # Simple Infix Expression Evaluation Using A Stack
# The expression must be fully parenthesized
# (meaning 1+2+3 must be expressed as "((1+2)+3)")
# and must contain only positive numbers
# and aritmetic operators.
# FB - 20151107
def Infix(expr):
expr = list(expr)
stack = list()
num = ""
while len(expr) > 0:
c = expr.pop(0)
if c in "0123456789.":
num += c
else:
if num != "":
stack.append(num)
num = ""
if c in "+-*/":
stack.append(c)
elif c == ")":
num2 = stack.pop()
op = stack.pop()
num1 = stack.pop()
if op == "+":
stack.append(str(float(num1) + float(num2)))
elif op == "-":
stack.append(str(float(num1) - float(num2)))
elif op == "*":
stack.append(str(float(num1) * float(num2)))
elif op == "/":
stack.append(str(float(num1) / float(num2)))
return stack.pop()
expr = "((1.7+((2.8*3.6)/(0-9.4)))-5)"
print expr
print Infix(expr), eval(expr)
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