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

void concat
(const char lstr[], const char rstr[], char outstr[])
{
    int i, j;

    i = j = 0;
    while (lstr[i] != '\0')
    {
        outstr[i] = lstr[i];
        ++i;
    }
    while ((outstr[i++] = rstr[j++]) != '\0')
        ;
}

int main(void)
{
    char lword[] = "foo";
    char rword[] = "bar";
    char outword[strlen(lword) + strlen(rword) + 1];

    concat(lword, rword, outword);
    printf("%s\n", outword);
}