Substring in c programming, c substring

Substring in c programming: c programming code to find a substring from a given string and for all substrings of a string, For example substrings of string "the" are "t", "th", "the", "h", "he" and "e" to find substring we create our own c substring function which returns a pointer to string. String address, length of substring required and position from where to extract substring are the three arguments passed to function. String.h does not contain any library function to directly find substring.

C substring code

#include <stdio.h>
#include <malloc.h>
 
char* substring(char*, int, int);
 
main() 
{
   char string[100], *pointer;
   int position, length;
 
   printf("Enter a string\n");
   gets(string);
 
   printf("Enter the position and length of substring\n");
   scanf("%d%d",&position, &length);
 
   pointer = substring( string, position, length);
 
   printf("Required substring is \"%s\"\n", pointer);
 
   free(pointer);
 
   return 0;
}
 
/*C substring function: It returns a pointer to the substring */
 
char *substring(char *string, int position, int length) 
{
   char *pointer;
   int c;
 
   pointer = malloc(length+1);
 
   if (pointer == NULL)
   {
      printf("Unable to allocate memory.\n");
      exit(EXIT_FAILURE);
   }
 
   for (c = 0 ; c < position -1 ; c++) 
      string++; 
 
   for (c = 0 ; c < length ; c++)
   {
      *(pointer+c) = *string;      
      string++;   
   }
 
   *(pointer+c) = '\0';
 
   return pointer;
}