Uses for Bitwise operators

EvenOrOdd.c

#include <stdio.h>
#include <stdlib.h>

/**
 * Checking whether a number is even or odd,
 * 
 * A base ten '2' is equal to a base-two '0010'. 
 * When using a bitwise 'and' on the numbers '0001' 
 * and '0010' there are no matching digits, meaning
 * a return of only zeros.
 * 
 * Pseudo-code
 * 
 * bool isEven(int input) {
 *     if ((input & 0001) > 0000)
 *         return false
 *     if ((input & 0001) == 0000)
 *         return true
 * }
 *
 * An example with an even and an odd number,
 * |   Comparee   |   Compared   |    Result    |
 * |    0010, 2   |    0001, 1   |      0       |
 * |    0011, 3   |    0001, 1   |      1       | 
 * |    0100, 4   |    0001, 1   |      0       |
 * |    0101, 5   |    0001, 1   |      1       |
 * |    0110, 6   |    0001, 1   |      0       |
 */
int main() 
{
    // The number to test.
    int x = 2;
    
    if (x & 1)
        printf("%d is odd.", x);
    else
        printf("%d is even.", x);
  
    return EXIT_SUCCESS;
}

PowersOfTwo.c

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int x = 32;
    
    /* If the number is less than 
     * zero, it's not a power of two. */
    if (x < 0) return;
    
    if ((x & (x - 1)) == 0)
        printf("%d is a power of two", x);
        
    return EXIT_SUCCESS;
}

ToLowercase.c

#include <stdio.h>
#include <stdlib.h>

#define     ASCII_MIN 65   // 01000001, 'A'
#define     ASCII_MAX 90   // 01011010, 'Z'
#define     NULL_TERM 0x00 // ASCII Null Terminator
#define ASCII_BITMASK 32   // 0x20, Bitmask between uppercase and lower values.

int main()
{
    char str[] = "HELLO, WORLD";

    to_lowercase(str);

    printf("%s\n", str);

    return EXIT_SUCCESS;
}

/**
 * In the ASCII table, the decimal values for the characters
 * 'A' to 'Z' are from 65 to 90, and 'a' to 'z' are from 97 to 122.
 * This method requires that we have a 6th bit, (32 decimal ->
 * which is '00100000' in binary) to 1 in ASCII.
 * Our bitwise OR operator here, with the value 32 set to the 6th bit to one
 * will effectively convert any uppercase characters to lowercase
 * characters until the string null terminator '\0' is reached.
 * 
 * @param str The inputted character array to be converted.
 */
void to_lowercase(char str[]) 
{
    for (int i = 0; str[i] != NULL_TERM; ++i) 
    {
        if (str[i] >= ASCII_MIN && str[i] <= ASCII_MAX)
            str[i] |= ASCII_BITMASK;
    }
}

toUppercase.c

#include <stdio.h>
#include <stdlib.h>

#define ASCII_MIN 97    // 01100001, 'a'
#define ASCII_MAX 122   // 01111010, 'z'
#define NULL_TERM 0x00  // ASCII Null Terminator 

int main()
{
    char str[] = "hello, world";

    to_uppercase(str);

    printf("%s\n", str);
    return EXIT_SUCCESS;
}

/**
 * Here, the bitwise AND operation is shifted with a 
 * negation of 1 shifted to the left by 5 bits.
 * This sets the 6th bit, (5 if you're counting from 1) to 0,
 * which is the bit that distinguishes lowercase letters from
 * uppercase letters in proper ASCII.
 *
 * Here's an example of this shift:
 * In this example we'll use the following, 
 * and it should output the next entrace in the table.
 *
 * CHARACTER  ASCII VALUE  BINARY VALUE
 *    'a'          97        01100001
 * TO ---         ----       --------
 *    'A'          65        01000001
 *
 * Bitwise Shift:   01100001 << 5       = 10000000
 * Bitwise AND:     10000000 & 11011111 = 01000001 
 * 01000001:        65 in decimal, ASCII value for 'A'.
 * 
 * @param str The inputted character array to be converted.
 */
void to_uppercase(char original[]) 
{
    for (int i = 0; original[i] != NULL_TERM; ++i) 
    {
        if (original[i] >= ASCII_MIN && original[i] <= ASCII_MAX)
            original[i] &= ~(1 << 5);
    }
}