Thread: Putting functions in a header file

Ok I am learning how to put functions that i write into a header file and then including that file in my source code. But I keep getting and error for undefined reference to rndNumber(), but the other function I have works fine when I call it. Here is the code to my header file:

Code:

#include <time.h>

int rndNumber(int range)
{
  int x,range; 
  srand((unsigned)time(NULL));
  x = rand()%range;
  return x;
}

void quit(void)
{
    char x;
    printf("Press q to quit.....");
    lbl1:
    while(kbhit() == 0);
    if(getch() != 'q')
           goto lbl1;
}

And here is the code to my .c file:

Code:

#include <stdio.h>
#include <myfunctions.h>

void quit(void);
int rndNumber(int range);

int main(int argc, char *argv[])
{
  int x;

  printf("Enter the range:\n");
  scanf("%i",&x);
  rndNumber(x);
  printf("The random number is %i\n",x);
  quit(); 	
  return 0;
}

>Ok I am learning how to put functions that i write into a header file

Don't put definitions in a header -- only declarations. I'd recommend something like this.

myfunctions.h:

Code:

#ifndef MYFUNCTIONS_H
#define MYFUNCTIONS_H

int rndNumber(int range);
void quit(void);

#endif

myfunctions.c:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <conio.h>
#include "myfunctions.h"

int rndNumber(int range)
{
  int x; 
  srand((unsigned)time(NULL));
  x = rand()%range;
  return x;
}

void quit(void)
{
    printf("Press q to quit.....");
    lbl1:
    while(kbhit() == 0);
    if(getch() != 'q')
           goto lbl1;
}

main.c:

Code:

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

int main(int argc, char *argv[])
{
  int x = rndNumber(6);
  printf("The random number is %i\n",x);
  quit(); 	
  return 0;
}

Code:

    lbl1:
    while(kbhit() == 0);
    if(getch() != 'q')
           goto lbl1;

This is such an insane waste of CPU cycles...

Code:

void quit(void)
{
    printf("Press q to quit.....");
    lbl1:
    while(kbhit() == 0);
    if(getch() != 'q')
           goto lbl1;
}
//better this way...
void quit(void)
{
    while(getch() != 'q');
    // use exit() if you want...
    exit(0);
}

About the undefined references:
if you're using an IDE and add your myfunctions.c and main.c to the default project, it should compile well.
If you're using a command line compiler, 1st you have to compile each of the *c. files separately and then link them all together.
Using gcc here's an examle:
1# gcc myfunctions.c -c
2# gcc main.c -c
3# gcc myfunctions.o main.o -o myprog.exe
or
4#gcc myfunctions.c main.c -o myprog.exe
On 1# and 2# you source files are compiled, and on 3# they're linked together to create a final executable.
That undefined reference happens because in your main.c you include myfunctions.h which declare a function that you use. That's only a declaration, something to mention the compiler that those symbols are funtions that receive x arguments and return something. Then when you link the final file the compiler MUST know here the compiled function is, the binaries.
4# is just a short hand for 1#,2# and 3#.
If you're working with a large project, separating your source through several files is a way to organize you code, and to reduce compilation time, because you only need to compile the file that you change, and re-link.