Problem compiling self-created header file using Dev-C++?

I am using Dev-C++ on windows vista. I have 3 files located in the same directory. They are:

- math_functions.h
- math_functions.c
- test3.c

math_functions.h code:

int   sum       (int x, int y);
float average   (float x, float y, float z);

math_functions.c code:

int sum (int x, int y)
{
  return (x + y);
}

float average (float x, float y, float z)
{
  return (x + y + z) / 3;
}

test3.c code:

#include <stdio.h>
#include "math_functions.h"

main ()
{
  int   theSum     = sum (8, 12);
  float theAverage = average (16.9, 7.86, 3.4);

  printf ("the sum is: %i ", theSum);
  printf ("and the average is: %f \n", theAverage);
  printf ("average casted to an int is: %i \n", (int)theAverage);
}

It fails to compile. The error message I get is:

C:\User开发者_JAVA技巧s\eSum\AppData\Local\Temp\ccKmdaaa.o(.text+0x3a) In function `main': 
[Linker error] undefined reference to `sum' 
[Linker error] undefined reference to `average' 
C:\Users\eSum\AppData\Local\Temp\ccKmdaaa.o(.text+0x3a) ld returned 1 exit status 

I use the same exact code compile in ubuntu(I run ubuntu using virtual machine i,e. vmplayer), it compiled without errors.

Do I need to set anything in Dev-C++ to compile the files?

Dev-C++ seems not to be linking math_function.c with test3.c when making text3.exe this is a configuration problem in Dev-C++ you most likely need to add math_function.c to the Dev-C++ project

The problem isn't with the header-file, but with your project settings. You have to add math_functions.c to the project so it gets compiled and linked with test3.c.