newbie question: "do while" loop parsing twice?

[Toscano]

Can somebody please explain why I'm getting a double print out of the actions inside the loop (a simple printf() message) every time I enter a character?

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>

main() {

  // Only pressing a numerical key will make a system call to clear the screen

  char x;

  do {
    printf("\nPress any numerical digit to clear the screen:");
    scanf("%c", &x);
  } while ( isdigit(x) == 0 );

  system("clear");


} // end of main()

The isdigit() validation seems to be working. What I'm not understanding is why the printf() message appears twice if I enter a character.

Thanks.

[Tclausex]

When you hit the enter key to signal processing of the keyboard buffer, you are also sending a newline character into the buffer. The second loop is from reading that newline.

Simple fix in this case is to put a space between the open-quote and the %c. It tells scanf to ignore and discard all leading whitespace.

Later on, you might find yourself needing to flush the entire buffer, so remember this for later:

while( getchar() != '\n' ) ;

[Toscano]

When you hit the enter key to signal processing of the keyboard buffer, you are also sending a newline character into the buffer. The second loop is from reading that newline.

Simple fix in this case is to put a space between the open-quote and the %c. It tells scanf to ignore and discard all leading whitespace.

Got it!

Later on, you might find yourself needing to flush the entire buffer, so remember this for later:

while( getchar() != '\n' ) ;

Nice. I'm really at the beginning, but I'll try to remember when I get to that.
Thanks!