Question

(PYTHON PLS)Write a program that will treat an equation like a stack. It will pop each character off of the stack to evaluate whether it is an operation, variable, constant or parenthesis. You will need to initialize each variable (with values prior to parsing the string which makes up the equation. For example it should be able to process (sin(sin(sin(sin(x))))) as well as 5X(T/3)-X.

Answer 1

ANSWER:

first you need to find the infix to postfix :

def infixToPostfix(infixexpr):

prec = {}
prec["*"] = 3
prec["/"] = 3
prec["+"] = 2
prec["-"] = 2
prec["("] = 1
opStack = Stack()
postfixList = []
tokenList = infixexpr.split()

for token in tokenList:
if token in "ABCDEFGHIJKLMNOPQRSTUVWXYZ" or token in "0123456789":
postfixList.append(token)
elif token == '(':
opStack.push(token)
elif token == ')':
topToken = opStack.pop()
while topToken != '(':
postfixList.append(topToken)
topToken = opStack.pop()
else:
while (not opStack.isEmpty()) and \
(prec[opStack.peek()] >= prec[token]):
postfixList.append(opStack.pop())
opStack.push(token)

while not opStack.isEmpty():
postfixList.append(opStack.pop())
return " ".join(postfixList)

print(infixToPostfix("A B + C D"))

then after for postfix evaluation :

def postfix_evaluation(s):
s=s.split()
n=len(s)
stack =[]
for i in range(n):
if s[i].isdigit():
#append function is equivalent to push
stack.append(int(s[i]))
elif s[i]=="+":
a=stack.pop()
b=stack.pop()
stack.append(int(a)+int(b))
elif s[i]=="*":
a=stack.pop()
b=stack.pop()
stack.append(int(a)*int(b))
elif s[i]=="/":
a=stack.pop()
b=stack.pop()
stack.append(int(b)/int(a))
elif s[i]=="-":
a=stack.pop()
b=stack.pop()
stack.append(int(b)-int(a))

return stack.pop()

#space separtor is required , for solving 2 or more digits .
s="10 2 8 * + 3 -"
val=postfix_evaluation(s)
print(val)

you can use output of first program as an input of secons program as s