Finding whether a string contains a duplicate or not?

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Here is a code which i wrote to find duplicates in a string . This code doesn't work. It uses pointers to the string . The pointer *first points to first element of the string and *second to second element . And the two pointers increment and loop thrrough the string and find the duplicates .this is how it is supposed to work ,correct me if i am wrong?

C#

#include<stdio.h>
main()
{
char string[]= "hello";
int len=strlen(string);
char *first=string;
char *second=string+1;
while(first <len-1 && second<len)
{
 if(*first==*second)
 {
  printf("A duplicate found\n");
 }
 first++;
 second++;
}
}

Posted 14-Aug-13 23:46pm

Member 10200096

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Maarten Kools 15-Aug-13 6:01am

You're comparing your pointer with the length of the string in your while loop (so it'll probably never get into the loop). Make sure your string is null-terminated, and then compare with null.

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OriginalGriff · Accepted Answer · 2013-08-15T00:00:00

Um.

First and second are both pointers. You are comparing them to integers? Do you think this is a good idea? What do you expect the result to be?

Instead, replace your while loop with a for loop:

C#

#include<stdio.h>
main()
      {
      int i;
      char string[]= "hello";
      int len=strlen(string);
      char *first=string;
      char *second=string+1;
      for (i = 0; i < len - 1; i++)
          {
          if(*first==*second)
              {
              printf("A duplicate found\n");
              }
          first++;
          second++;
          }
      }