I have a C program which is meant to return the repeating characters and their frequencies from a given input string. At the moment, it works fine, however I was wondering if there was a way I could change it so it would return characters in order of appearance, as opposed to alphabetical(?) order.

# include <stdio.h>
# include <stdlib.h>
#include <ctype.h>
# define NO_OF_CHARS 256

char fillCharCounts(unsigned char *str, int *count)
{
   int i;
   for (i = 0; *(str i);  i  )
      count[*(str i)]  ;
return 0;
}

void printDups(unsigned char *str)
{
  int *count = (int *)calloc(NO_OF_CHARS,
                             sizeof(int));
  fillCharCounts(str, count);


int dupe_chars = 0; 
int i;
    for (i = 0; i < NO_OF_CHARS; i  )
        if (count[i] > 1) {
            printf ("\nDuplicate letter: %c, Occurrences: %d", i, count[i]);
              dupe_chars; 
        }

    if (0 != dupe_chars)
        printf ("\n");        
    else
        printf ("\nNo duplicates found\n");

  free(count);
}

int main()
{
    unsigned char str[15] = "";
    printf("Enter a word>");
    scanf("%s", str);
    printDups(str);
    getchar();

return 0;
}

At the moment, if the input string were say "zzbbaa" it would give the output;

"Duplicate: a, count: 2" "Duplicate: b, count: 2" "Duplicate: z, count: 2"

How can I change this so the output returns the duplicates in order of appearance in the string?

CodePudding user response：

You can go through the string again, printing out the duplicate the first time it's found.

Here's code as I would write it. There's no need for dynamic allocation of memory -- the count array can go on the stack, and *(str i) is much better written str[i].

#include <stdio.h>
#include <limits.h>

void printDups(unsigned char *s) {
    int count[UCHAR_MAX 1] = {0};
    int dupes = 0;
    for (int i = 0; s[i]; i  ) {
        count[s[i]]  ;
        dupes = dupes || (count[s[i]] > 1);
    }
    for (int i = 0; s[i]; i  ) {
        if (count[s[i]] > 1) {
            printf("Duplicate letter: %c, Occurrences: %d\n", s[i], count[s[i]]);
            count[s[i]] = 0;
        }
    }
    if (!dupes) {
        printf("No duplicates found\n");
    }
 }

int main(int argc, char**argv) {
    unsigned char s[] = "hello world";
    printDups(s);
}