Thread: modular programming

hello i'm writing this code to teach myself programming with modules, but obviously theres something wrong since my compiler says

Compiling BPS.C:
Linking bps.exe:
Linker Warning: No module definition file specified: using defaults
Linker Error: Undefined symbol _output in module BPS.C
Linker Error: Undefined symbol _input in module BPS.C

Code:

//inout.c
#include<stdio.h>
#include"inout.h"

static void stars (void);		//prints out a line of *, local function prototype defined here


int input(void){                                     //prototype in header		

    char c;
    int res,keuze;

    stars ();
    printf("   1. BPM 2 FPS\n   2. FPS 2 BPM\n\nkeuze: ");
    stars ();

    while((res=scanf("%d%c",&keuze,&c))!=2 || c!='\n' || keuze<1 || keuze>2){
        scanf("%*[^\n]%*c");
        printf("tik 1 of 2");
	}

return keuze;
}

void output(int keuze){
    printf("uw keuze is %d",keuze);
}

static void stars(void){

    int i;

    for(i=0; i<30; i++){
        putchar('*');
    }

}

Code:

//inout.h

int input(void);
void output(int keuze);

Code:

//bps.c
#include<stdio.h>
#include"inout.h"

int main (void){

	int keuze;

	keuze=input();
	output(keuze);



return 0;
}

all files are stored in same directory, so why isnt this working?

gcc compiled it. You are compiling bps.c or bpm.c? I compiled like this:
gcc -c inout.c
gcc -c bpm.c
gcc -s inout.o bpm.o -o bpm