Calculator in C++ using if-else-if Looping Construct

#include <iostream>

int output;    
char op;
int data;    

int main(  )
{
    output = 0; 

    while (true) {
        std::cout << "output: " << output << '\n';
        std::cout << "Enter operator and number: ";

        std::cin >> op >> data;

        if ((op == 'q') || (op == 'Q'))
            break;

        if (op == '+') {
            output += data;
        } else if (op == '-') {
            output -= data;
        } else if (op == '*') {
            output *= data;
        } else if (op == '/') {
            if (data == 0) {
                std::cout << "Error:Divide by zero\n";
                std::cout << "   operation ignored\n";
            } else
                output /= data;
        } else {
            std::cout << "Unknown operator " << op << '\n';
        }
    }
    return (0);
}