C - Why does this loop run through twice?

Question

This function is suppose to go back 1 step in the connect 4 game, however, it goes back twice... I went through the function with a debugger, and it seems to skip the getc() call I don't know why. Any help is much appreciated!

char UndoBoard(char x[ROWS][COLS], char * player){
    struct Node* temp = head;
    int i,j;
    temp = temp->next;
    char input = 'q';
    while((input != 'q' || input != 'Q') && temp != NULL){
        for (i=0;i<ROWS;i++){
            for (j=0;j<COLS;j++){
            x[i][j] = temp->data[i][j];
            }
        }
        printBoard(x);
        if(*player == 'O')*player = 'X';
        else *player = 'O';
        printf("b - undo one step more, f - go forward, q - resume game from here\n");
        input = getc(stdin);
        if(input == 'q' || input == 'Q')break;
        temp = temp -> next;
    }
}

Answer 1

The logic used in

while((input != 'q' || input != 'Q') && temp != NULL){

is faulty. You need to use:

while((input != 'q' && input != 'Q') && temp != NULL){

Answer 2

Your condition for input in the while condition is wrong. One of the two terms will be true, regardless of the value of input , so the loop only terminates here if temp != NULL .

But you actually break on user input later in the loop using a correct expression, so there is actually no need to test in the loop condition. Instead, use only temp here:

while ( temp != NULL ) {

Now you can also change

char input = 'q';

to

char input;

because it is now not before user input is read in the loop.

Note that getc returns an int , not a char to provide EOF , you also should test for. (thanks to @chux for pointing me at this).

As you just use it inside the loop, you can move it, to (all changes included):

while ( temp != NULL ) {
    int input;

    ...

    if ( input == EOF || input == 'q' || input == 'Q' )
        break;

    temp = temp->next;
}