Thread: reverse string

I have written code to reverse string. I am stuck with my logic. I know string is null terminated in c language so array hold total 6 character including NULL terminator

Code:

#include <stdio.h>

int main()
{
    int i = 0;
    char array[6]= {"NEERG"};
	char temp = array[0];
	              
    for ( int i = 0; i < 5; i++)
    {
        for (int  j = 6; j >= 0; j--)
        {
                temp =  array[i];
                array[i] = array[j];
                array[j] = temp;        
        }           
    }
   
    printf("%s", array);
   
    return 0;
}

Program output

Code:

REEN

all the letters are getting reverse but G is missing in string

How to reverse all letters

You don't need nested loops for this. A single loop is enough. Swap the first and last character, then swap the second character and second-to-last character, etc. That is, swap array[i] with array[len-i] (where len is the length of the string). Iterate while i is less than len-i.

Code:

#define swapch_(a,b) { char t; t = (a); (a) = (b); (b) = t; }

char *strrev( char *s )
{
  char *p, *q;

  p = s;
  q = s + strlen( s ) - 1;

  while ( p < q )
  {
    swapch_( *p, *q );
    p++; q--;
  }

  return s;
}

I assume, you are a beginner like me and thus I will provide an example, using an array.

Code:

#include <stdio.h>

int main() {
    int j = 4;
    int tmp = 0;
    char array[6]= {"NEERG"};
    int i;
    for (i = 0; i < 3; i++) {   // swap only needs half of string
        tmp = array[j];
        array[j] = array[i];    // you can also use array[j--] = array[i];
        j--;                    // and drop this line
        array[i] = tmp;
    }

    printf("%s", array);

    return 0;
}

Today, I would use pointers and other stuff.

I will strongly advice you to learn the use of a debugger, so you step by step, can follow the code.

You should also consider the case where the swapped characters are identical.

In this code, the loop is necessary to iterate through the entire array. The goal is to reverse the elements in the array, which requires looping through the entire array and swapping the elements. A pointer for the start of the array and another for the end of the array would not accomplish this goal since the elements must be swapped in order to reverse the array.

Originally Posted by Vithika

In this code, the loop is necessary to iterate through the entire array. The goal is to reverse the elements in the array, which requires looping through the entire array and swapping the elements. A pointer for the start of the array and another for the end of the array would not accomplish this goal since the elements must be swapped in order to reverse the array.

Yeah, you are right. This doesn't work!

Code:

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

int main(int argc, char ** argv) {
  char test_str[] = "G4143's test string";
  char * bgn_str = test_str;
  char * end_str = test_str + strlen(test_str) - 1;
  fprintf(stdout, "%s\n", test_str);
  while (bgn_str < end_str) {
    if (*bgn_str != *end_str) {
      char temp = *bgn_str;
      *bgn_str = *end_str;
      *end_str = temp;
    }
    ++bgn_str;
    --end_str;
  }
  fprintf(stdout, "%s\n", test_str);
  return 0;
}

Originally Posted by Vithika

Code:

#include <stdio.h>

int main()
{
    int i = 0;
    char array[6]= {"NEERG"};
    char temp = array[0];
                  
    for ( int i = 0; i < 6; i++)
    {
        for (int  j = 5; j >= 0; j--)
        {
                temp =  array[i];
                arrayI[i] = array[j];
                array[j] = temp;        
        }           
    }
   
    printf("%s", array);
   
    return 0;
}
Program output
Code:
GREEN

Your code doesn't even compile (arrayI is undeclared), and it has the same flaw as OP's (it doesn't work correctly).

If you actually built it (after fixing the arrayI issue) and ran it, you would see that it prints "EEN".

It baffles me why people don't actually test their code before posting it (especially for such short and simple bits of code like this).

Thanks to both of you for boosting up the self-esteem 😒