Thread: Can't figure this out

Hello, I'm working on an exercise in my book. It tells you to write a program that will print out the first n prime numbers, where n is inputed by the user.

My output is should like this (which it does):

Primes
--------
2
3
5
7
...


The program should have 3 files, a prime.h which has all the preprocessing directives, a is_prime.c file which has the function to determine if a number is prime and prime.c which contains the main function.

Here's what all three looks like:

prime.h

Code:

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

int is_prime( int n );

is_prime.c

Code:

#include "prime.h"


int is_prime( int n ){
	int k, limit;
	
	if( n == 2) return 1;
	if( n % 2 == 0) return 0;
	limit = n / 2;
	for( k = 3 ; k <= limit ; k += 2 )
		if( n % k == 0 ) return 0;
	return 1;
}

and finally prime.c (the main program)

Code:

#include "prime.h"


int main(void){
	int i=2, n, count=0;
	
	printf("Howw many prime number do you want to see? ");
	scanf("%d", &n );
	
	printf("Primes\n------\n");

	while(1){	
		if( is_prime( i ) ){
			count++;
			printf("%3d: %d \n", count, i);
		}
		i++;
		if( count == n ) break;	
	}
	return 0;
}

My problem is, when I compile with these 3 files I get an error:

Unresolved external '_is_prime' referenced from prime.obj

but if I put all the code in one file it works fine, what am I doing wrong?

Try using 'extern' to make your function available.

Code:

extern int is_prime( int n )

Originally posted by aqua
include this statement in your main program(prime.c)


#include "is_prime.h"

i put the line:

Code:

#include "is_prime.c"

in my prime.c and it works, but shouldn't it work anyways since I already included the line:

Code:

#include "prime.h"

Right???