Calling scanf() after another string input function creates phantom input

Question

Here\'s a small program:

#include 

int main() {
  char str[21], choice[21]; int size;
  while(1){
    printf(\"$ \");
    fgets(str, 20, stdin);
         


        

Answer 1

It because the scanf call reads a character, but leaves the newline in the buffer. So when you next time call fgets is finds that one newline character and reads it resulting in an empty line being read.

The solution is deceptively simple: Put a space after the format in the scanf call:

scanf("%s ", choice);
/*       ^    */
/*       |    */
/* Note space */

This will cause scanf to read and discard all training whitespace, including newlines.