Why is my c != 'o' || c != 'x' condition always true?

Question

I have this loop statement, which I'll express using C-like syntax (C, C++, Java, JavaScript, PHP, etc. all use similar syntax):

while (c != 'o' || c != 'x') {
    c = getANewValue();
}

I want it to run until I get a 'o' or 'x', but it never exits, even when c is 'o' or 'x'. Why not?

I've also tried using if:

if (c != 'o' || c != 'x') {
    // Show an error saying it must be either 'o' or 'x'
}

but that also always shows the error message, even when c is 'o' or 'x'. Why?

Answer 1

It must be if(c!='o' && c!='x') instead of if(c!='o' || c!='x'). If you use the or operator the boolean expression will be always true.