程序打印两次相同的打印语句

Question

My program is working fine and everything but I want it to be perfect. So I've stumbled up on this problem that when my function runs, it prints out the same printf() statement twice.

Let me show you what I mean, this is how my function looks (skipping main/prototypes)

void decision2(struct CardDeck *deck) {
char choice;
int Ess;
printf("\n%s, Your have %d\n", deck->name2, deck->ValueOfSecondPlayer);
while (deck->ValueOfSecondPlayer <= 21)
{
    if (deck->ValueOfSecondPlayer == 21) {
        printf("You got 21, nice!\n");
        break;
    }
    if (deck->ValueOfSecondPlayer < 21) {
        printf("Would you like to hit or stand?\n");
        scanf("%c", &choice);
    }
    if (choice == 'H' || choice == 'h') {
        printf("You wish to hit; here's your card\n");
        Ess = printCards(deck);
        if (Ess == 11 && deck->ValueOfSecondPlayer > 10)
        {
            Ess = 1;
        }
        deck->ValueOfSecondPlayer += Ess;
        printf("Your total is now %d\n", deck->ValueOfSecondPlayer);
        if (deck->ValueOfSecondPlayer > 21) {
            printf("Sorry, you lose\n");
        }
    }
    if (choice == 'S' || choice == 's') {
        printf("You wished to stay\n");
        break;
    }
}

}

So the thing in my code thats weird is this part:

    if (deck->ValueOfSecondPlayer < 21) {
        printf("Would you like to hit or stand?\n");
        scanf("%c", &choice);
    }

The output of the program is becoming this:

    k, Your have 4
Would you like to hit or stand?
Would you like to hit or stand?
h
You wish to hit; here's your card
6 of Clubs
Your total is now 10
Would you like to hit or stand?
Would you like to hit or stand?
h
You wish to hit; here's your card
King of Diamonds
Your total is now 20
Would you like to hit or stand?
Would you like to hit or stand?
s
You wished to stay

As you see, the printf prints the statement twice and I can't figure out the program to be honest, so I hope someone do have a solution and an explanation why this is happening?

Answer 1

The problem here is, with

 scanf("%c", &choice);

it reads the previously stored newline (entered into the input buffer by pressing ENTER key after the first input) and performs one more iteration. You should write

 scanf(" %c", &choice);  //note the space here
       ^^

to avoid the newline.

To elaborate, the leading space before the %c ignores any number of leading whitespace character(s) [FWIW, a newline is a whitespace character] and wait to get a non-whitespace input.

Answer 2

There has to be a space before %c in scanf() , to clear the previously entered newline \\n :

scanf(" %c", &choice);

Without the space, scanf() will scan the newline and jump to the beginning of the loop again (after skipping the remaining if statements), skipping the first if() , and print "Would you like to hit or stand?\\n" a second time.