Scanning character in a while loop

Question

char player_select(void){

    char player = 'n';

    while(player == 'n'){
        printf("Select your player (X or O): ");
        scanf("%c\n", &player);

        if(player != 'X' && player != 'O'){
            printf("Invalid input. Try again.\n");
            player = 'n';
        }
    }

printf("Your character input is: %c\n", player);
exit(0);
return player;
}

I am getting some weird output here:

Select your player (X or O): X

Invalid input. Try again.

Select your player (X or O): i

Your character input is: X

chux · Accepted Answer · 2014-02-25 21:52:44Z

3

Incorrect use of scanf()

// scanf("%c\n", &player);
scanf(" %c", &player);

The '\n' in "%c\n" does not do what you think. '\n' tells scanf() to consume white-space like '\n' and ' ' until non-white-space occurs. You input was not as described.

Since stdin is buffered, text by itself, will not typically get read until a '\n' follows.

It gets complicated to explain in detail why things failed. So briefly, use " %c" instead of "%c\n". Or better yet, use fgets().

buffer player[10];
fgets(ch, sizeof ch, stdin);
if(player[0] != 'X' && player[0] != 'O') { ...

edited Feb 25, 2014 at 21:52

answered Feb 25, 2014 at 21:46

chux

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Comments

WileTheCoyot · Accepted Answer · 2014-02-25 21:56:29Z

1

I hope this will work for you. I have removed the \n inside the scanf and i have added while(getchar()!='\n'); for emptying stdin.

char player_select(void){

char player = 'n';

while(player == 'n'){
    printf("Select your player (X or O): ");
    scanf("%c", &player);

    if(player != 'X' && player != 'O'){
        printf("Invalid input. Try again.\n");
        player = 'n';
    }
    while(getchar()!='\n');
}

This is the output:

Select your player (X or O): A
Invalid input. Try again.
Select your player (X or O): X
Your character input is: X

edited Feb 25, 2014 at 21:56

answered Feb 25, 2014 at 21:47

WileTheCoyot

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1 Comment

chux Over a year ago

Suggest while(getchar()!='\n'); outside the if() block to consume the \n if user enters a bad or good char.

Niloct · Accepted Answer · 2014-02-25 21:39:24Z

0

Try:

    if (scanf("%c\n", &player) == 1 && player != 'X' && player != 'O'){
        printf("Invalid input. Try again.\n");
        player = 'n';
    }

Bring scanf into the if, removing from your above code, and check its return value == 1.

You can try removing the \n from scanf mask if this won't suffice.

answered Feb 25, 2014 at 21:39

Niloct

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