To Remove the duplicate characters from a String

Given a string, remove the repeated characters from the string and print the unique characters of the string.
For Example: If the given string is "abcdcbad"
                       then the output string is "abcd"

#include <stdio.h>
#include<stdlib.h>
#include<string.h>
int main(void) {
 /* This method uses hashing technique */
 char *p="abcdefghijklmnopqrstuvwxyzzyxwvutsrqponmlkjihgfedcba"; //Input string
 char s[55];
 int i=0;
 int hash[26];
 /* Initializing hash array to zero */
 memset(hash,0,sizeof(hash));
 while(*p)
 {
  /* If the hash index of the character is not visited, copy the character to output array */
  if(hash[*p-'a']==0)
  {
   *(s+i)=*p;
   i++;
  }
  /* mark the hash index of the character as visited*/
  hash[*p-'a']=1;
  /* Increment the string pointer to traverse the string */
  p++;
 }
 /* Mark the end of the result string with Null character '\0' */
 *(s+i)='\0';
 printf("%s",s);
 return 0;
}