Input in C. Scanf before gets. Problem

Question

I'm pretty new to C, and I have a problem with inputing data to the program.

My code:

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

int main(void) {
   int a;
   char b[20];

   printf("Input your ID: ");
   scanf("%d", &a);

   printf("Input your name: ");
   gets(b);   

   printf("---------");

   printf("Name: %s", b);   

   system("pause");
   return 0;
}

It allows to input ID, but it just skips the rest of the input. If I change the order like this:

printf("Input your name: ");
   gets(b);   

   printf("Input your ID: ");
   scanf("%d", &a);

It will work. Although, I CANNOT change order and I need it just as-is. Can someone help me ? Maybe I need to use some other functions. Thanks!

Answer 1

scanf doesn't consume the newline and is thus a natural enemy of fgets. Don't put them together without a good hack. Both of these options will work:

// Option 1 - eat the newline
scanf("%d", &a);
getchar(); // reads the newline character

// Option 2 - use fgets, then scan what was read
char tmp[50];
fgets(tmp, 50, stdin);
sscanf(tmp, "%d", &a);
// note that you might have read too many characters at this point and
// must interprete them, too

Answer 2

scanf will not consume \n so it will be taken by the gets which follows the scanf. flush the input stream after scanf like this.

#include <stdlib.h>
#include <string.h>

int main(void) {
   int a;
   char b[20];

   printf("Input your ID: ");
   scanf("%d", &a);
   fflush(stdin);
   printf("Input your name: ");
   gets(b);   

   printf("---------");

   printf("Name: %s", b);   

   system("pause");
   return 0;
}