In Dev-C++, Why cannot I compile my project although I imported the project required files?

Question

In Dev-C++, I want to make a project to sort a table and that's why I brought the source files into my project. but when I want to compile my project, compiler gives me an error and it can't identify functions.

This is my first source file.

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#define LENGTH 5

I saved the first file in the computer as "Preprocessors.c".

The second source file :

void Selective_sorting(int Table[], int Length)
{
     int *Temporary;
     int Smallest_index;

     for(register short int Outside = 0; Outside < Length; Outside++)
     {
         Smallest_index = Outside;

         for(register short int Inside = (Outside + 1); Inside < Length; Inside++)
         {
             if(*(Table + Inside) < *(Table + Smallest_index))
                 Smallest_index = Inside;
         }

         Temporary = (int*) malloc(sizeof(int));
         if(!Temporary)
         {
             printf("An error occurred while allocating memory.\n");
             exit(1);
         }

         *Temporary = *(Table + Smallest_index);
         *(Table + Smallest_index) = *(Table + Outside);
         *(Table + Outside) = *(Table + Smallest_index);

         free(Temporary);
     }
 }

I saved the second source file in the computer as "Selective_func.c".

And the third source code to run the program :

int main()
{
    int table[5] = {9, 7, 6, 5, 3};
    Selective_sorting(table, 5);

    for(register short int Counter = 0; Counter < 5; Counter++)
    printf("%d\n", *(table + Counter));

    return 0;
}

I saved the third source file in the computer as "Main_func.c".

And I brought the source files into my project and when I compiled the project, this error occurred:

Answer 1

You're not including files correctly.

Your main file needs to include the headers it needs: like stdlib.h and stdio.h but also a header that defines void Selective_sorting(int Table[], int Length);.

Then your implementation file should also include that same header with the void Selective_sorting(int Table[], int Length); prototype + any header files needed for things it uses (e.g. stdio.h because you use printf()).

Basically you should always remember that any C file (either .c or .h) you want to compile doesn't know about any function, variable or type (except for system built-in ones) if you don't include the header file that defines it.