Playing with String Functions

Question

This is a very small question, and probably something really silly! But why am I getting garbage returned in my output for this function which should remove double letters?

#include <stdio.h>
#include <string.h>
#include <ctype.h>

char  *makehello( char *s ) {
   char new[16] ;
   int i ;
   int c = strlen(s);
   for ( i = 0; i < (c + 1); i++)
     if (toupper(s[i]) != toupper(s[i+1]))
       new[i] = toupper(s[i]);
return strdup( new ) ;  
}

int main(void) {
 char *new;
 char data[100];
 scanf("%s", data);
 new = makehello(data);
 printf("%s", new);
return 0;
}

Im just playing atm with aabb aacc etc to test it, but getting garbage printed :/ — PnP
– PnP, Commented Nov 24, 2011 at 16:51
Make sure you terminate the result. Initialise it as char new[16] = { 0 };. — Kerrek SB
– Kerrek SB, Commented Nov 24, 2011 at 16:53
Im not getting any compiler warnings, just getting garbage printed. Not sure why at all though. — PnP
– PnP, Commented Nov 24, 2011 at 17:03

DaV · Accepted Answer · 2011-11-24 17:10:34Z

2

You need a separate count for your 'new' array. You're storing them at index 'i' (where you found the character), but what you really want is to store them from position 0 and increment this count instead.

EDIT: Of course this isn't a fullproof method.

i.e something like this:

   for ( i = 0; i < c; i++)
   {
        if (toupper(s[i]) != toupper(s[i+1]))
        {
            new[count++]= toupper(s[i]);
        }
   }
   new[count] = '\0';

edited Nov 24, 2011 at 17:10

answered Nov 24, 2011 at 17:03

DaV

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Comments

Ed Heal · Accepted Answer · 2011-11-24 17:01:56Z

0

The line

for ( i = 0; i < (c + 1); i++)

should be

for ( i = 0; i < (c - 1); i++)

And you then need before the strdup new[i]=0;

Braces would not go amise either.

EDIT

Forgot need to change the following

int i, j=0;

and in the for loop

new[j++] = toupper(s[i]);

and after the for loop

new[j] = 0;

edited Nov 24, 2011 at 17:01

answered Nov 24, 2011 at 16:55

Ed Heal

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2 Comments

PnP Over a year ago

Im still getting garbage output :/

PnP Over a year ago

i.e. bbb returns just garbage output

Kerrek SB · Accepted Answer · 2011-11-24 17:18:05Z

0

Here's a reasonably compact C99 version of the algorithm (headers omitted, example):

const char * makehello (const char * s)
{
  char new[16] = { *s, 0 };
  const char * p = s;
  char c = *s, * q = new;

  while (*p) { if (*++p != c) { c = *++q = *p; } }

  return strdup(new) ;
}

int main(void)
 {
  char data[100];
  scanf("%s", data);
  printf("%s", makehello(data));
  return 0;
}

(This one discriminates case.)

answered Nov 24, 2011 at 17:18

Kerrek SB

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