My program doesn't create a txt file when I think it should

Does anyone have any idea why this program doesn't write whether the input number is a prime or not to a txt file?

Code:

#include <values.h>
#include <limits.h>
#include <stdio.h>
#include <process.h>
#include <conio.h>

int write_function();

int main(void)
{
   printf("                     Welcome to the Prime Number Program\n");
   printf("This program will determine if a number is a prime number.\n");

   write_function();

   getch();
   return 0;
}

int write_function()
{
   FILE *prime_file;
   int number, i, remainder;
   int not_divisible = 1;
   int biggest = 1;
   prime_file = fopen("prime_io.txt", "w");

   printf("Enter a number(e.g. 1972): ");
   scanf("%d", &number);
   for( i = 2; i < number - 1; i++ )
   {
      remainder = number % i;
      if(remainder == 0 )
      {
         not_divisible = 0;
         biggest = i;
      }
   }

   if(not_divisible == 1)
      fprintf(prime_file, "\nThe number %d is a prime number", number);
   else
      fprintf(prime_file, "\nThis number's highest divisor is %d and thus is not prime", biggest);
   fclose(prime_file);
}

You could always let your program tell you why it's not. replace:

Code:

prime_file = fopen("prime_io.txt", "w");

with:

Code:

if(!(prime_file = fopen("prime_io.txt", "w")))
{
  perror("fopen()");
  return;
}

You'll also need to #include <errno.h>
Or at the very least do:

Code:

if(!(prime_file = fopen("prime_io.txt", "w")))
{
  puts("Couldn't open file for writing!");
  return;
}

I get call to function write_function with no prototype, eventhough I have declared a prototype.

The program actually does run, but when I enter in a number, then press enter, the program doesn't display whether it is prime or not, and it doesn't create a txt file.

Any ideas?

Could anyone still help me out here? tell me if you know something, I'm an idiot if that's what it takes.

in your prototype you need to declare your function arguments as void

Code:

int write_function(void);

It works perfectly for me. In order to get it to compile without warnings, I had to change the function prototype & definition to include void as sandman did, and include a return 0; at the end of write_function() (since it's declared to return an int). But then it created prime_io.txt very nicely and with the correct contents.