Command Line Simple Calculator

#include<iostream>
#include <cstdlib>
#include <cstring>
using namespace std;

int main(int argc, char *argv[] ){

    int a = strtoul(argv[1],NULL,0);
    string op = argv[2];
    int b = strtoul(argv[3],NULL,0);
    int answer = 0;

    if(op == "+"){
        answer = a + b;
    }
    else if(op == "-"){
        answer = a - b;
    }
    else if(op == "*"){
        answer = a * b;
    }
    else if(op == "/"){
        answer = a / b;
    }

    cout << a << " " << op << " " << b << " = " << answer << endl;
    //cout << op << endl;

    return 0;
}