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

#define maxlength 256

void reversePuts(const char s[]);
char *strprecat(const char *s1, char *s2);

int main(void)
{
    char s1[maxlength] = "pre string.";
    char s2[maxlength] = "ANIMATION";

    putchar('\n');
    puts(s1);
    reversePuts(s1);

    puts(s2);
    reversePuts(s2);

    putchar('\n');
    puts(s1);
    puts(s2);
    putchar('\n');
    puts(strprecat(s1,s2));
    putchar('\n');
    puts(s1);
    puts(s2);

    return 0;
}

void reversePuts(const char s[])
{
    const char *c = s + strlen(s);
    while (c > s)
        putchar(*(--c));
    putchar('\n');
}

char *strprecat(const char *s1, char *s2)
{
    int i, l1 = strlen(s1), l2 = strlen(s2);
    if (l1 + l2 >= maxlength)
        return 0;
    for (i = l2; i >= 0; i--) // the null character at the end of s2 is moved too.
        s2[i + l1] = s2[i];
    for (i = 0; i < l1; i++)
        s2[i] = s1[i];
    return s2;
}