Comparison inside while loop c++

Question

I am trying to make when user types number, program should repeat that many times chosing random if Here is my code

cin >> d;
c = 0;

while (c < d) {
    c = c++;
    num = (rand() % 3) + 1;
    if (num == 1) {
        system("start C:\\viewver\\vw");
        Sleep(2000);
    }
    else if (num == 2) {
        system("start C:\\viewver\\vw2");
        Sleep(2300);
    }
    else if (num == 3) {
        system("start C:\\viewver\\vw3");
        Sleep(1800);
    }

It always chooses to open first one and then stops.

Typo: `(num = 1)` is always `true`. Crank your compiler warnings up a little. And `c = c++;` is UB currently. — Bathsheba, Apr 24 '18 at 15:25
and this is very odd too `c = c++;`, not even sure if it has well defined behavior — pm100, Apr 24 '18 at 15:27
@Bathsheba - And even if it's not... better treat it like it is UB ;) — StoryTeller - Unslander Monica, Apr 24 '18 at 15:27
`c = c++` [is unspecified behavior](https://stackoverflow.com/questions/4968854) — Drew Dormann, Apr 24 '18 at 15:28
@DrewDormann: No, in C++14 and earlier it's undefined. This epitomises why you shouldn't trust everything you read on the internet. — Bathsheba, Apr 24 '18 at 15:40

score 0 · Accepted Answer · answered Apr 24 '18 at 15:29

Use == not =

if (num == 1) {
    system("start C:\\test\\vw");
    Sleep(2000);
}
else if (num == 2) {
    system("start C:\\test\\vw2");
    Sleep(2300);
}
else if (num == 3) {
    system("start C:\\test\\vw3");
    Sleep(1800);
}

== is for comparison, = is for assignment

The reason why it always chooses the first option is because C++ (and C) has the notion of truthy values. So any value that is not 0 is considered truthy, whereas values that evaluate to 0 are considered falsy.

In your original code, when you assign num to 1, the value of num is truthy, therefore that branch is always taken

it changed so it will always choose last option, but it will open only once and stop. — Dokido, Apr 24 '18 at 16:09

Comparison inside while loop c++

1 Answers1