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

void main(){
	char mystring[] = "There was a gerbil in the sink";

	for(char *start = mystring, *end = mystring + strlen(mystring)-1; start < end;){
		*start += *end;
		*end = *start - *end;
		*start -= *end;
		start++;
		end--;
	}

	printf("mystring = %s\n", mystring);
}