The below C program takes two input a,b but when executed it asks for another null input before printing the sum of a,b. Why?

Question

#include <stdio.h>
#include<conio.h>
int main()
{
int a,b;
printf("Enter the value of a&b:\n");
scanf("%d %d ",&a,&b);
printf("Sum:%d",a+b);
return 0;
}

Answer 1

But what actually happens when we add a whitespace at the end in the format specifiers?