K&R(3.5): Loops-For

#include <stdio.h>
#include <string.h>
#define MAX 1000  /* max size of the array */
void reverse(char s[]);
/* reverse a string in place */
int main()
{
    char s[MAX];
    int c, i;
    i = 0;
    while ((c = getchar())!= EOF && i < MAX)
        s[i++] = c;
    printf("The origin string is %s ", s);
    reverse(s);
    printf("The reversed string is %s\n", s);
    return 0;
}

/* reverse: reverse string s in place */
void reverse(char s[])
{
    int c, i, j;

    for (i = 0, j = strlen(s)-1; i < j; i++, j--) {
        c = s[i];
        s[i] = s[j];
        s[j] = c;
    }
}