Reverse array in C recursively

Question

Here's a part of my code, where I am trying to reverse a string recursively:

    char reverse[10];
    gets(reverse);
    reverseString(reverse, (strlen(reverse) - 1));
    void reverseString(char ar[], int n)
    {
        if (n == 0)
        {
            return;
        }
        else
        {
            int temp = ar[n];
            ar[n] = *(ar);
            *(ar) = temp;
            reverseString((ar + 1), (n - 1));
        }
    }

When I enter the string "hello" it changes the string to "ohell". I need it to reverse the string totally to "olleh". Can someone help?

try to make building blocks. reverse by swapping complete blocks, and once they're swapped recursively swap the internals of the block. — Alexander Oh
– Alexander Oh, Commented Mar 2, 2014 at 13:16
Use a debugger to see what is actually being replaced. You'll be surprised... — zmbq
– zmbq, Commented Mar 2, 2014 at 13:17
Never use gets, it's not even in the latest standard anymore. — Arkku
– Arkku, Commented Mar 2, 2014 at 13:29

Martin R · Accepted Answer · 2014-03-02 13:19:12Z

5

Since you swap the first and last element of the array, you should recursively call the function with the remaining n-2 elements (instead of n-1),

void reverseString(char ar[], int n)
{
    if (n <= 0)
    {
        return;
    }
    else
    {
        int temp = ar[n];
        ar[n] = *(ar);
        *(ar) = temp;
        reverseString((ar + 1), (n - 2));
    }
}

(I have assumed that reverseString and reverseAr in your code are actually the same functions, perhaps some copy-paste error.)

answered Mar 2, 2014 at 13:19

Martin R

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3 Comments

zmo Over a year ago

there's also an error for odd length strings that is solved in your answer, with the stop condition n <= 0.

Martin R Over a year ago

@zmo: Regarding your comment to the now deleted answer: The reverse of "653421" should be "654321" and not "653421".

zmo Over a year ago

damn, I'm getting dyslexic on sundays :-s

sreenivas · Accepted Answer · 2014-03-02 13:20:02Z

0

# include <stdio.h>

/* Function to print reverse of the passed string */
void reverse(char *str)
{
   if(*str)
   {
       reverse(str+1);
       printf("%c", *str);
   }
}

/* Driver program to test above function */
int main()
{
   char a[] = "Geeks for Geeks";
   reverse(a);
   getchar();
   return 0;
}

answered Mar 2, 2014 at 13:20

sreenivas

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1 Comment

zmo Over a year ago

it looks like the OP wants in place reversal of the string.

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