为什么我的代码在 Visual Studio 中不起作用？

Question

this is my code

#include <conio.h>
#include <iostream>

using namespace std;

int main() {
    bool a = false;
    char b='p';
    int c=0;

    while (a != true) {
        if (_kbhit()) {
            b = _getch();
        }
        if (b=='w') {
            c++;
            cout << c << " ";
       }
        else if (b == 'c') {
            cout << "hello";
        }
    }
    system("pause");
    return 0;
}

The problem is where when I press 'w' I want it to print out the value of c and it should be repeating until i press another input for _kbhit() right? because now it add 1 to c then prints c and when i press w again samething. What's wrong with my visual studio I'm using community 2017 I've tried to uninstall it and install it again but same problem occurs.

Answer 1

The problem you're running into seems to be a result of a recently added bug in _getch() / _kbhit .

For an extended key (eg, a cursor key) it's documented that _getch() returns either a 0x0 or 0xe0 followed by the scan code for the key that was actually pressed. What's not documented is that if the user presses a non-extended key, _kbhit will still return true twice in succession, and calls to _getch() will return the key code the first time, and 0x0 the second time.

In your code, when the user presses 'w' or 'c', _kbhit will return true not just once (as you'd expect) but twice . The first time you call it, it'll return the scan code of the key, and the second it'll return a 0 byte.

What's happening in your code is that you're reading the scan code, printing something appropriately, then _kbhit is returning true again, so you read the '\\0' byte, set b to '\\0', and then (since you don't have any code to do anything when b is 0) you (repeatedly) do nothing until the next time the user presses a key.

Reference

https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/getch-getwch?view=vs-2017

Answer 2

It seems like the program behaves the way you want it to. If I press 'w', it goes into an infinite loop of increasing the value of c and printing it. Pressing any other key stops printing and pressing 'c' goes on the same infinite loop and prints hello . Doesn't seem to be any problems as far as the posted code is concerned. Also, I would like to say the same as @Someprogrammerdude, if it compiles, but doesn't behave the way you want it to, it's an issue with the code, not the IDE and/or compiler.

Hypothetical answer: Your computer might always be thinking that a key is pressed, thus kbhit() always returns true. This maybe caused by a bad mouse/keyboard/controller driver and/or configuration. The code is fine, your PC is not.