#include <stdio.h>

char *strcat(char *s, const char *t);
char *strcpy(char *t, const char *s);
size_t strlen(const char *s);

/* passes args to strcat, prints result */
int main(int argc, char *argv[])
{
    if (argc < 3)
        return 1;
    char s[strlen(argv[1]) + strlen(argv[2])];
    strcat(strcpy(s, argv[1]), argv[2]);
    printf("%s\n", s);
}

/* strcat: concat string t to end of string s */
char *strcat(char *s, const char *t)
{
    int slen = strlen(s);
    return strcpy(s + slen, t) - slen;
}

/* strcpy: copy string s to t */
char *strcpy(char *t, const char *s)
{
    char *tc = t;
    while ((*t++ = *s++))
        ;
    return tc;
}

/* strlen: return length of string s (without \0) */
size_t strlen(const char *s)
{
    const char *sc = s;
    while (*s++)
        ;
    return s - sc - 1;
}