How to Check Palindrome String in C ?

What is Palindrome?
 
It's a word, phrase, or sequence that reads the same backwards as forwards, e.g. malayalam , madam or nurses run.

 
#include <stdio.h>
#include <conio.h>

int is_palindrome(char*);
void copy_string(char*, char*);
void reverse_string(char*);
int string_length(char*);
int compare_string(char*, char*);

main()
{
   char string[100];
   int result;

   printf("Enter a string\n");
   gets(string);

   result = is_palindrome(string);

   if ( result == 1 )
      printf("\"%s\" is a palindrome string.\n", string);
   else
      printf("\"%s\" is not a palindrome string.\n", string);

   return 0;
}

int is_palindrome(char *string)
{
   int check, length;
   char *reverse;

   length = string_length(string);   
   reverse = (char*)malloc(length+1);   

   copy_string(reverse, string);
   reverse_string(reverse);

   check = compare_string(string, reverse);

   free(reverse);

   if ( check == 0 )
      return 1;
   else
      return 0;
}

int string_length(char *string)
{
   int length = 0; 

   while(*string)
   {
      length++;
      string++;
   }

   return length;
}

void copy_string(char *target, char *source)
{
   while(*source)
   {
      *target = *source;
      source++;
      target++;
   }
   *target = '\0';
}

void reverse_string(char *string)
{
   int length, c;
   char *begin, *end, temp;

   length = string_length(string);

   begin = string;
   end = string;

   for ( c = 0 ; c < ( length - 1 ) ; c++ )
       end++;

   for ( c = 0 ; c < length/2 ; c++ )
   {       
      temp = *end;
      *end = *begin;
      *begin = temp;

      begin++;
      end--;
   }
}

int compare_string(char *first, char *second)
{
   while(*first==*second)
   {
      if ( *first == '\0' || *second == '\0' )
         break;

      first++;
      second++;
   }
   if( *first == '\0' && *second == '\0' )
      return 0;
   else
      return -1;
}