/*
 * reverse a string recursively
 *
 * Matt Bishop, ECS 36A, Fall 2019
 */
#include <stdio.h>
#include <string.h>

/*
 * reverse str recursively
 * this works by swapping the first and last character
 * then reversing what's between them, stopping when
 * there are 0 or 1 characters to reverse
 *
 * str = array containing (sub)string to reverse
 * b = index of first element in s(sub)string to be reversed
 * e = index of last element in s(sub)string to be reversed
 */
void reverse(char *str, int b, int e)
{
	char tmp;	/* used to swap two chars */

	/* base case; if 0 or 1 character, return */
	if (b >= e)
		return;
	
	/* now swap the beginning and end character */
	tmp = str[b];
	str[b] = str[e];
	str[e] = tmp;

	/* and reverse the middle */
	reverse(str, b + 1, e - 1);

}

/*
 * the program to run
 */
int main(void)
{
	char str[100];	/* input string */

	/* read in a line, and clobber any trailing newline */
	if (fgets(str, 100, stdin) == NULL)
		return(1);
	if (str[strlen(str)-1] == '\n')
		str[strlen(str)-1] = '\0';

	/* say what the string is */
	printf("'%s' reversed is ", str);

	/* now reverse it and say what that is */
	reverse(str, 0, strlen(str)-1);
	printf("'%s'\n", str);

	/* bye! */
	return(0);
}