Strings - General Questions

What will be the output of the program?

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

int main(void) {
    char s[] = "Hello";
    printf("%zu %zu\n", strlen(s), sizeof(s));
    return 0;
}

What will be the output of the program?

#include <stdio.h>
#include <ctype.h>

int main(void) {
    char s[] = "HeLLo";
    int i, up = 0;
    for (i = 0; s[i]; i++) if (isupper((unsigned char)s[i])) up++;
    printf("%d\n", up);
    return 0;
}

Which function compares at most n characters of two strings?

What will be the output of the program?

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

int main(void) {
    char s[] = "racecar";
    int i = 0, j = (int)strlen(s) - 1, ok = 1;
    while (i < j) if (s[i++] != s[j--]) ok = 0;
    printf("%d\n", ok);
    return 0;
}

Which header must be included to use strlen?