#include <assert.h>
#include <string.h>
#include <stdbool.h>
#include <ctype.h>

char *to_upper_subtraction(char *s) {
    for (int i = 0; s[i]; i++) {
        if (s[i] >= 'a' && s[i] <= 'z') {
            s[i] -= 32; // or in hex `0x20`
        }
    }
    return s;
}

char *to_upper_bitwise(char * s) {
    for (int i = 0; s[i]; i++) {
        if (s[i] >= 'a' && s[i] <= 'z') {
            s[i] &= 0b11011111; // or in hex `~0x20`
        }
    }
    return s;
}

bool case_insensitive_compare_bitwise(char *s1, char *s2) {
    for (int i = 0; s1[i] && s2[i]; i++) {
        if (isalpha(s1[i]) && isalpha(s2[i])) {
            // Alphabetical character
            // Compare ignoring case
            if ((s1[i] | 0b00100000) != (s2[i] | 0x20)) {
                return false;
            }
        } else {
            // Non-Alphabetical character
            // Normal comparison
            if (s1[i] != s2[i]) {
                return false;
            }
        }
    }
    return true;
}

int main(void) {
    char s1[] = "Hello, World!";
    char s2[] = "Hello, World!";
    assert(0 == strcmp("HELLO, WORLD!", to_upper_subtraction(s1)));
    assert(0 == strcmp("HELLO, WORLD!", to_upper_bitwise(s2)));

    char s3[] = "HeLLo, WOrLD!";
    char s4[] = "hEllo, WORld!";
    assert(case_insensitive_compare_bitwise(s3, s4));
}