What happens when you use a printf() function inside another printf() function. To understand this lets see the following example:

#include<stdio.h>
int main() {
  int number = 1234;
  printf("%d", printf("%d", printf("%d", number)));
  return(0);
}

Output:

  123441

Explanation of the above program::

1. The "innermost" printf() function prints the value of the number i.e., "1234"

2. The second printf() function will now be as

   printf("%d", 4); 

   it's because the first printf() function will return 4 as the total number of digits in original "number" and it will print "4".

   The output will now be "12344"

3. The last printf() fiunction will now be as

   printf("%d", 1);

   it's because the second printf() function will return 1 as the total number of digits(i.e., 4 is a single digit number) and it will print "1".

   The output will now be "123441".