Concatenate two strings without using strcat

Question

I wrote a function to concatenate two strings (s = "computer"; t = "keyboard"), but my code only returns "keyboard". Please point out the mistakes.

char *concat(char *s, char *t) {
    s = malloc((strlen(s) + strlen(t) + 1) * sizeof(char));
    char *p = s;
    while (*p != '\0') {
        ++p;
    }
    while (*t != '\0') {
        *p++ = *t++;
    }
    *p = '\0';
    return s;
}

I do not want to use strcat(). This is a test program from Stepik, so I cannot change anything in the main function. Here is the question: Write a function which receives two character pointers and returns a new character pointer representing their concatenation.

Answer 1

char *myconcat(const char *s1, const char *s2)
{
    size_t len1,len2;
    char *result = malloc((len1 = strlen(s1)) + (len2 = strlen(s2)) + 1);

    if(result)
    {
        memcpy(result, s1, len1);
        memcpy(result + len1, s2, len2 + 1);
    }
    return result;
}