Conflicting Types error

i'm writing a simple program for my programming class and i can't get rid of this "conflicting types" error.

Code:

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

main( )
{
  printf ("1 \n"); // 1
  printf ("2 \n"); // 2
  printf ("3 \n"); // 3
  printf ("4 \n"); // 4
  printf ("5 \n"); // 5
  f1 ( );
  printf ("6 \n"); // 6
  printf ("7 \n"); // 7
  printf ("8 \n"); // 8
}
void f1 (void)
{
     printf ("f1-9 \n"); // 9
     printf ("f1-10 \n"); // 10
     f2 ( );
     printf ("f1-11 \n"); // 11
     printf ("f1-12 \n"); // 12
}
     void f2 (void)
{
     printf ("f2-13 \n"); // 13
     printf ("f2-14 \n"); // 14
     printf ("f3-15 \n"); // 15

  system("PAUSE");	

}

the errors say: conflicting types for 'f1', conflicting types for 'f2'
what should i do?

 

You haven't declared f1 () and f2 () BEFORE you use them. C will therefore presume that they accept an int and return an int. When you call them, you call them as accepting a void and returning a void. Either put the definitions ABOVE main, or put a declaration (prototype) above main.