Question

I want to reverse a string in the C language. I’m kinda new, so I would love to get some help and explanation. Why doesn’t my solution work?

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

char *rev(char *str) {
  char *q = str;
  int len = strlen(str);
  char *p = (char*)calloc(len+1, sizeof(char));
  int j=0;
  if (NULL == str || len == 1) return str;
  for (j = len+1 ; j > 0 ; j-- ) {
    p[j]=*q;
    q++;
  }
  return p;
}

int main(int argc, char **argv){
  char *t = argv[1];
  char *p ;
  printf("%s",t);
  p=rev(t);
  printf("%s",p);
  getchar();
  return 0;
}

It’s not working 🙁

Answer 1

You have to be careful with your indices at the boundaries.

One way to fix is replace your for line with this:

for (j = len-1; j >= 0 ; j-- )