A C code to reverse a string

Question

Does anybody see the bug here? I have got alternate solutions.

int main()
{

  char line[100], res[100], temp[20];
  fgets( line, 100*sizeof(char), stdin);    
  int i, j, l;
  for( i=strlen(line)-1; i>=0; i--)
  {
    if(line[i]==' ')
        for(j=i+1, l=0; line[j]!=' ' && line[j]!='\0'; l++, j++)
            temp[l]=line[j];
    temp[++l]=' ';
    temp[++l]='\0';
    strcat(res, temp);
  }
  puts(res);
  return 0;
}

Please tell us what behaviour you are actually seeing and how it differs from the expected behaviour. — ChrisF, Apr 25 '15 at 17:20
Never do this `for( i=strlen(line)-1; i>=0; i--)`, you are computing the length of the string `length` of the string times, you should know that `strlen()` loops through the characters to count them. — Iharob Al Asimi, Apr 25 '15 at 17:21
`strcat(res, temp);` - that isn't good. You never setup `res[]` as a terminated buffer, and `strcat` expects it to be so. So the hunt is on to find a `0` char, and if you're (un)lucky, you find one with enough space left over to actually concatenate your source string. — WhozCraig, Apr 25 '15 at 17:26

score 0 · Answer 1 · answered Apr 25 '15 at 17:31

0

l and j are initialized just when line[i]==' '.

Witch won't be the case for the first iteration, where line[i] would be '\n'

answered Apr 25 '15 at 17:31

Pedro Witzel

368
3
14

score 0 · Answer 2 · answered Apr 25 '15 at 17:44

The for and if loop are not required. Since the array follows 0 based indexing, i should take values from 0 to strlen(line)-1, so j=i+1 should be j=i (line 1). Strings should be null terminated - line 2. Also, l is already incremented in the for loop, so instead of pre-increment, use post-increment (or do not use it at all) (line 3).

#include<stdio.h>
#include<string.h>
int main()
{

 char line[100], res[100], temp[20];
 fgets( line, 100*sizeof(char), stdin);
 int i, j, l=0;
 res[0]='\0';   //line 2
 i=strlen(line)-1;

    for(j=i, l=0; line[j]!=' ' && line[j]!='\0'; l++, j--) //line 1
        {temp[l]=line[j];
         }
   temp[l++]=' ';   //line 3 (or temp[l]=' ')
   temp[l++]='\0';

   strcat(res, temp);

  puts(res);
  return 0;
}

A C code to reverse a string

2 Answers2