Writing String Functions

my_strlen — the canonical walk

int my_strlen(const char* s) {
    int n = 0;
    while (s[n] != '\\0') n++;
    return n;
}

Read the loop as: "advance until the terminator". The idiom version:

int my_strlen(const char* s) {
    const char* p = s;
    while (*p) p++;
    return (int)(p - s);
}

my_strcmp — compare while both agree

int my_strcmp(const char* a, const char* b) {
    while (*a && *a == *b) {   // stop at terminator or first difference
        a++;
        b++;
    }
    return (unsigned char)*a - (unsigned char)*b;
}

If the loop ended because both hit '\0', the difference is 0. Otherwise it is the code difference at the first mismatch.

my_strcpy — copy WITH the terminator

void my_strcpy(char* dst, const char* src) {
    while (*src) {
        *dst = *src;
        dst++;
        src++;
    }
    *dst = '\\0';              // the step beginners forget
}

Copy characters, then copy the terminator. Without that last line the destination is not a string.