c substring

#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;
}