postfix_evaluation.cpp

//Program to postfix evaluation using stack data structure
#include<bits/stdc++.h>
using namespace std;
float scanNum(char ch) {
   int value;
   value = ch;
   return float(value-'0');  
}
int isOperator(char ch) {
   if(ch == '+'|| ch == '-'|| ch == '*'|| ch == '/' || ch == '^')
      return 1;   
   return -1;   
}
int isOperand(char ch) {
   if(ch >= '0' && ch <= '9')
      return 1;  
   return -1;  
}
float operation(int a, int b, char op) {
  
   if(op == '+')
      return b+a;
   else if(op == '-')
      return b-a;
   else if(op == '*')
      return b*a;
   else if(op == '/')
      return b/a;
   else if(op == '^')
      return pow(b,a); 
   else
      return INT_MIN; 
}
float postfixEval(string postfix) {
   int a, b;
   stack<float> stk;
   string::iterator it;
   for(it=postfix.begin(); it!=postfix.end(); it++) {
      
      if(isOperator(*it) != -1) {
         a = stk.top();
         stk.pop();
         b = stk.top();
         stk.pop();
         stk.push(operation(a, b, *it));
      }else if(isOperand(*it) > 0) {
         stk.push(scanNum(*it));
      }
   }
   return stk.top();
}
int main() {
   string exp; 
   cout<<"Enter postfix expression : ";
   cin>>exp;
   
   cout << "The value of given expression is  : "<<postfixEval(exp);
   
   return 0;
}