Can anyone explain why this code returns 1 on every input?

Question

#include <stdio.h>

int main() {
int a;
printf("%d", scanf("%d", &a));
return 0;
}

But in option -1 is the answer how -1 will be the answer

Answer 1

Quoting

http://www.cplusplus.com/reference/cstdio/scanf/

"On success, the function returns the number of items of the argument list successfully filled."

In your case, scanf() fills one item in the argument list, and returns 1.

Answer 2

~ swim ~

Answer 3

As scanf returns the number of conversions that were successfully made, the example program will either print a 1, a 0 or a -1, depending on the provided input (1 if the start of the input is convertible to an integer, 0 for non-integer input, -1 for input errors).

Answer 4

Does that too an case or any other explanation for that behavior