postfixEval.cpp

#include "stack.hpp"

using namespace std;


int isOperator(char c){
   switch (c) {
    case '+':
        return 1;
    case '-':
        return 1;
    case '*':
        return 1;
    case '^':
        return 1;
    case '/':
        return 1;
    }
    return 0;
}

int main(){
  freopen("input_postfixEval.txt", "r", stdin);
  string s;
  int solution;
  int line_counter = 0;
  while(cin>>solution){
    cin>>s;
    Stack<int> stack;
    
    // The input file is in the format "expected_solution postfix_expression"

    // We assume that all operands in the input are one digit (so they range from 0 to 9)
    for(int i=0; i<s.length(); ++i){
      // WRITE CODE HERE to evaluate the postfix expression in s
      // At the end of the loop, stack.pop() should contain the value of the postfix expression
      char ch = s[i];
      if (ch >= '0' && ch <= '9'){
          int num = ch-'0';//converting to int
          stack.push(num);
      }

      if (isOperator(ch))
      {
        int rOperand = stack.peek();
        stack.pop();
        int lOperand = stack.peek();
        stack.pop();
        int tempAns=0;
        if (ch == '+')
        {
          tempAns=rOperand+lOperand;
        }
        else if(ch == '-'){
          tempAns=lOperand-rOperand;

        }
        else if(ch == '*'){
          tempAns=rOperand*lOperand;
        }
        else if(ch == '/'){
          tempAns=lOperand/rOperand;
        }
        else if(ch == '^'){
          for (int i = 0; i < rOperand; i++)
          {
            lOperand*=lOperand;
          }
          tempAns=lOperand;
        }
        stack.push(tempAns);
      }
      

    }

    // Checking whether the value you calculated is correct ...
    int value = stack.pop();

    if(solution == value){
      cout << "line " << line_counter << ": OK [" << solution << " " << value << "]" << endl;
    }else{
      cout << "line " << line_counter << ": ERROR [" << solution << " " << value << "]" << endl;
    }
    line_counter++;
  }

}