/*
 * Program to define and demonstrate a function that reversese
 * a string in place.  (Example of working with strings using pointers.)
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void reverse_in_place(char * string);

int main(void) {
	char line[80];
	printf("enter a line of text\n");
	fgets(line, sizeof line, stdin);
	/* if input fits into array, fgets stores '\n' character */
	char *nl = strchr(line, '\n');
	if (nl == NULL) {
		printf("line too long\n");
		return EXIT_FAILURE;
	}
	*nl = '\0';

	printf("input '%s'\n", line);
	reverse_in_place(line);
	printf("reversed '%s'\n", line);

	return EXIT_SUCCESS;
}

/*
 * Reverse a string in place/
 * Strategy:  Define two pointers that initially point to the
 * ends of the string.  Loop, moving them toward the middle until
 * they meet, swapping a pair of characters at each step.
 */
void reverse_in_place(char * string) {
	char * left = string;
	char * right = string + strlen(string) - 1;
	while (left < right) {
		char tmp = *left;
		*left = *right;
		*right= tmp;
		++left;
		--right;
		/* more compact though less readable 
		   char tmp = *left++;
		 *left = *right;
		 *right--= tmp;
		 */
	}
}