Postfix Evaluator


// Postfix Evaluator 
// Name - Tirthraj Mahajan

#include <iostream>
#include <stack>
#include <string>
#include <cmath>
#include <stdexcept>
using namespace std;

bool isOperand(char ch){
    if (ch!='+'&&ch!='-'&&ch!='*'&&ch!='/'&&ch!='('&&ch!=')'&&ch!='^') {
        return true;
    }
    else{
        return false;
    }
}

int operation(char ch, int a, int b) {
    switch(ch) {
        case '+':
            return a + b;
        case '-':
            return a - b;
        case '*':
            return a * b;
        case '/':
            if (b != 0) {
                return a / b;
            } else {
                throw invalid_argument("Division by zero");
            }
        case '^':
            return int(pow(a, b));
        default:
            throw invalid_argument("Unsupported operation");
    }
}

int evaluation(string postfix){
    // A Temporary variable to store the string to interger conversion
    int num;

    // Stack to handle the postfix expression
    stack<int> st;

    for(int i=0; i<postfix.length(); i++){

        // if the current element in postfix expression is an operand, then "try" to convert that 'char' into 'int' using try catch block and stoi function given in std::string class in C++11 or more
        // You can also use stringstream from sstream library to convert string into integer

        if(isOperand(postfix[i])){

            try{
                num = stoi(string(1, postfix[i])); //convert char to string before stoi function
                st.push(num);
            }
            catch(const invalid_argument &e){
                cout<<"Invalid Argument Error! Please enter numbers"<<endl;
                return -1;
            }
        }
        else{
            int a, b, c;
            b = st.top();
            st.pop();
            a = st.top();
            st.pop();
            c = operation(postfix[i],a,b);
            st.push(c);
        }

    }

    return st.top();
}

int main() {
    string postfix = "15+";
    cout<<"Evaluation: "<< evaluation(postfix)<<endl;

    return 0;
}


// Postfix Evaluator
// Name: Tirthraj Mahajan 


function isOperand(val){
    if(val=='('||val==')'||val=='+'||val=='-'||val=='/'||val=='*'||val=='^'||val=='–'){
        return false;
    }
    return true;
}



function operation(a, b, operation){
    switch(operation){
        case '+':
            return a+b;
            break;
        case '-':
            return a-b;
            break;
        case '–':
            return a-b;
            break;
        case '*':
            return a*b;
            break;
        case '/':
            return a/b;
            break;
        case '^':
            return a**b;
            break;
        default:
            console.log("Invalid Operation ", operation);
            return 0;
    }

}


let numStack = [];
function evaluate(expression){
    let expressionArr = expression.split(" ");
    console.log("Expression Array: ",expressionArr);
    let stack = [];
    for(let i=0; i<expressionArr.length; i++){
        if(isOperand(expressionArr[i])){
            stack.push(expressionArr[i]);
            numStack.push(Number(expressionArr[i]));
        }else{
            let b = stack.pop();
            let a = stack.pop();
            stack.push(`(${a} ${expressionArr[i]} ${b})`); 
            let num2 = numStack.pop();
            let num1 = numStack.pop();
            numStack.push(operation(num1,num2,expressionArr[i]));
        }
    }
    return stack[stack.length-1];

}

let postfix = "10 5 +";
console.log(evaluate(postfix));
if(!isNaN(numStack[numStack.length-1])){
	console.log("Evaluation Result : ",numStack[numStack.length-1]);
}