Hi, I have a program that I just wrote, but really its just a program that will be used by a larger program that I am working on. The larger program will run some functions in the small program, accessing some of its global arrays/variables to extract information.

I never knew how to create a header file so that this large program can include it. I think what i use to do was just "include small_prog.c" but I know thats not correct.

So how do we go about creating a header file?

The small program basically has:
-1 global array variable pointer
-3-4 int variables
- includes math.h, time.h, stdio.h, stdlib.h ctype.h
- #define MAX_ARRAY_SIZE 100
- a main function (only used if your running the file on its own)
- several functions that perform instructions to modify the above variables.

an example of this could be:
----------------------------------
small_prog.c

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
#include <time.h>


#define MAX_ARRAY_LENGTH 100
int* matrix_array;
int dimension=0;
int matrix_mode=0;
int x = 0;

void func1 (int x);
float func2 (float y);
int func3 (char a);

int main(int argc, char* argv[])
{
....
.
.
and so on
----------------------------------

So I want to include this small program in a large program, by refering to a .h file. but what do i write in the h file?
Jenna

Header file contains function prototypes, structure declarations, constant definitions, like #define.

//
// MODULE1.H FILE:
//
void func1 (int x);
float func2 (float y);
int func3 (char a);

Source file contains function bodies. It is preferred that names of both files are same, but they have different extension, like MODULE1.H and MODULE1.C:

//
// MODULE1.C FILE:
//
#include "MODULE1.H"

void func1 (int x)
{
    // ... your implementation here ...
}

float func2 (float y)
{
    // ... your implementation here ...
}

int func3 (char a)
{
    // ... your implementation here ...
}

After these TWO files are done they are used in a project - or you call it a large program. Usually, the development environment which you use has the ability to insert files into project. You need to insert both files into projects and then just "#include "<small_prog>.h"" into other C files of the project where you need those functions.

If you do not have an environment (like Dev-C++ or Visual C++ or something else...) then "include <small_prog>.c" is the way to go.

There are few other ways: like to compile the C file into .OBJ file and then use LINK tool to build the full program. It is usually done by the environment, but you can also do it manually - using command line tools.