Thread: recursion

hi.. I am suppose to write a recursive function that reverses the characters from s[j] to s[k] without changing the following main program:

Code:

int main (void)  {
char phrase [] = "by the sea, by the beautiful sea";
rev (phrase,3,17);
printf ("%s\n",phrase);
return 0;
}

and the output is "by eht yb, aes eht beautiful sea"

I wrote the following program, but i had to change the main function! i dont know how to do it without changing the main! plz HELP!

Code:

# include <stdio.h>

void rev (char [],int,int);
int main ()  {
char phrase [] = "by the sea, by the beautiful sea";
rev (phrase,3,17);  /* reverse the characters from phrase [3] to phrase [17] */
return 0;
}

void rev (char sen [],int start, int end)
{
if (end >= start)
printf ("%c",sen [end]);
rev (sen,start,end-1);
}

When looking at your recursive function it seems to me that it never ends, since rev() is always called. To solve that problem you should think about the two basic questions in recursion:

- when does the recursion stop
- what is the recursion step

If you solve these questions, then you have the answer to your problem.