/*
Evaluation Of postfix Expression in C++
Input Postfix expression must be in a desired format.
Operands must be integers and there should be space in between two operands.
 operands only have one num number.It's not fit like: 23 45*
Only '+'  ,  '-'  , '*' and '/'  operators are expected.
*/
/**pseudo code
 * Evaluatepostfix(exp)
 * {
 * create a stack S
 * for i =0 to legth(exp)-1
 * {
 * if(exp[i] is operand)
 * s.push(exp[i])
 * else if(exp[i] is operator)
 * {
 * op1 =top()
 * pop()
 * op2 = top()
 * pop()
 * result <--perform(exp[i],op1,op2)
 * push(res)
 * }
 *
 *
 * }
 *
 * }
 *
 */
#include <iostream>
#include <stack>
#include<queue>
using namespace std;

// Function to evaluate Postfix expression and return output
int EvauatePostfix(string expression)
{
// Declaring a Stack from Standard template library in C++.
    stack<int> stack1;
    int temp, operand1, operand2;
    for (int i = 0; i < expression.size(); i++) {

        // Scanning each character from left.
        // If character is a delimitter, move on.
        if (expression[i] == ' ' || expression[i] == ',')
            continue;


        else if (expression[i] >= '0' && expression[i] <= '9') {
            stack1.push(expression[i] - '0');
        }

            // If character is operator, pop two elements from stack,
            // perform operation and push the result back.
        else if (expression[i] == '+' || expression[i] == '-' || expression[i] == '*' || expression[i] == '/') {
            operand2 = stack1.top();
            stack1.pop();
            operand1 = stack1.top();
            stack1.pop();
            switch (expression[i]) {
            case '+':temp = operand1 + operand2;
                stack1.push(temp);
                break;
            case '-':temp = operand1 - operand2;
                stack1.push(temp);
                break;
            case '*':temp = operand1 * operand2;
                stack1.push(temp);
                break;
            case '/':temp = operand1 / operand2;
                stack1.push(temp);
                break;
            default:cout << "Unexpected Error \n";
                return -1;

            }
        }
        else
            cout << "Unexpected Error \n";
        return -1;

    }
    return temp;
}
int main()
{ //parse the postfix expressions
    //test string string string1 = "23*54*+9-";
    string expression;
    cout << "Enter Postfix Expression \n";
    getline(cin, expression);
    int result = EvauatePostfix(expression);
    cout << "Output=" << result << endl;

    // std::cout << "Hello, World!" << std::endl;
    return 0;
}