Why does my code stop even though if statement is false

Question

in this small chess terminal app, at the end of black's turn, the code should check if move contains '#' if so, it should exit. The problem is, it automatically exits and doesn't check the second if statement, looping it back to label. Why is this?

#include <iostream>

int main(){
    bool turn = true;
    int turnNumber = 0;
    bool mated = false;

    label:
    while(turn){

        std::string move;
        std::cout << "White to move: ";
        std::cin >> move;
        std::cout << move << '\n';
        turn = false;
    }

    while(!turn){

        std::string move;
        std::cout << "Black to move: ";
        std::cin >> move;
        std::cout << move << '\n';
        turn = true;
        turnNumber+=1;

        if(move.find('#')){
            mated = true;
        }

        else if(!mated){
            goto label;
        }
    }
}

I tried switching the statements around and removing the else, but that didn't work.

`goto` leads to hard to understand control flow and this code is a good example of that. — 463035818_is_not_an_ai, Jul 21 '23 at 19:24
`while(turn){...}` and `turn = false` as last statement inside the loop makes no sense. I think you want `if (turn) { ...}` — 463035818_is_not_an_ai, Jul 21 '23 at 19:25
`std::string::find` does not work the way you think. It returns the position of the character. The only way `if(move.find('#'))` can evaluate to false is when the first character is `#` — 463035818_is_not_an_ai, Jul 21 '23 at 19:28
This doesn’t adding the question, but get rid of that `goto`. `while (!mated) …`. — Pete Becker, Jul 21 '23 at 21:38
[What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — Jesper Juhl, Jul 22 '23 at 00:02
Too bad you don't use C++23, because then you could use `if(move.contains('#'))`. [string.contains](https://en.cppreference.com/w/cpp/string/basic_string/contains) — BoP, Jul 22 '23 at 09:02

Shivam Bansal · Answer 1 · 2023-07-22T06:14:02.437

#include <iostream>

int main(){
    bool turn = true;
    int turnNumber = 0;
    bool mated = false;

    label:
    while(turn){

        std::string move;
        std::cout << "White to move: ";
        std::cin >> move;
        std::cout << move << '\n';
        turn = false;
    }

    while(!turn){

        std::string move;
        std::cout << "Black to move: ";
        std::cin >> move;
        std::cout << move << '\n';
        turn = true;
        turnNumber+=1;

        if(move.find('#') != std::string::npos){
            mated = true;
        }

        else if(!mated){
            goto label;
        }
    }
}

This is your updated code. What was happening is, .find() method returns the first occurence of the given char or string. If it doesn't find one, it always return string::npos value (can be verified using this before you check that if condition):

std::cout << move.find('#') << endl;

and this value is always true. So it goes inside the if part.

The solution to it is checking with that value itself. If it is not equal to the npos value, that means the string contains '#', else not.

Why does my code stop even though if statement is false

1 Answers1