exercise4-13.md

Exercise 4-13

Write a recursive version of the function reverse(s), which reverses the string s in place

Process

Used the same process as the previous exercise of a static variable that is initialised on the first call

I like this process because

• it maintains the function signature of reverse(s) and doesn't require any external variables.
• it can just be called by the user without noticing a difference from the original function
• it's fairly procedural with a little amount branching, which I think makes it pretty easy to read and understand

A downside might be that it's longer, but maybe that's ok?

Code

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

void recursive_reverse(char s[])
{
    static int i, j, calls;
    char temp;
    
    /* inital call */
    if(calls == 0) {
        i = 0, j = strlen(s) - 1;
        calls = 1;
    }
    
    /* swap */
    temp = s[j];
    s[j] = s[i];
    s[i] = temp;
    
    i++, j--;
    
    if(i < j)
        recursive_reverse(s);
    
    calls = 0; /* reset */
}

int main()
{
    char str[] = "hello world";
    printf("%s\n", str);
    recursive_reverse(str);
    printf("%s\n", str);
    recursive_reverse(str);
    printf("%s", str);
    return 0;
}

Output

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