%d placeholder input '3abc', cannot clear 'abc' buffer

Question

Below is my code:

int length;
char ch;

printf("\n\tEnter the length of the password: ");
while (scanf("%d", &length) != 1) {

    printf("\n\tPlease enter digit only.\n");
    printf("\n\tEnter the length of the password: ");

    while ((ch = getchar()) != '\n' && ch != EOF);
}

printf("\n\tEnter the number of passwords you want: ");
while (scanf("%d", &num) != 1) {

    printf("\n\tPlease enter digit only.\n");
    printf("\n\tEnter the number of passwords you want: ");

    while ((ch = getchar()) != '\n' && ch != EOF);
}

When I entered abc okay.

When I entered 3abc, 3 is received by length, but the 'abc' still in the buffer.

I used while ((ch = getchar()) != '\n' && ch != EOF); to clear but still not working?

Any help from the expert is appreciated.

Answer 1

You are not flushing the stdin if a number was correctly grabbed by scanf as your test case 3asc

 int length;
 int ch;

 printf("\n\tEnter the length of the password: ");
 while (scanf("%d", &length) != 1) {

     printf("\n\tPlease enter digit only.\n");
     printf("\n\tEnter the length of the password: ");

     while ((ch = getchar()) != '\n' && ch != EOF);
 }

 // flush stdin
 while ((ch = getchar()) != '\n' && ch != EOF);

 printf("\n\tEnter the number of passwords you want: ");
 while (scanf("%d", &length) != 1) {

     printf("\n\tPlease enter digit only.\n");
     printf("\n\tEnter the number of passwords you want: ");

     while ((ch = getchar()) != '\n' && ch != EOF);
 }

And, already commented, to recognize ch != EOF ch must be int. Moreover getchar prototype is int getchar(void)