Can we declare functions inside functions?

Question

#include <stdio.h>

int main()
{
   void foo();
   printf("1 ");
   foo();
}

void foo()
{
    printf("2 ");
}

Output:

1 2

How declaring functions inside functions work? Does it mean that foo() function can only be called by main()?

Answer 1

Yes, you can declare, but you cannot define. Also, you can declare function as many times you want, but define only once.