C Integer Promotion

#include <stdio.h>
#include <stddef.h>

int main(void) {
    char a = 10;
    char b = 20;

    // 'a' and 'b' are individually promoted to 'int' before the addition.
    // The resulting expression yields an 'int'.
    size_t size_of_result = sizeof(a + b); 
    
    printf("sizeof(char): %zu byte(s)\n", sizeof(char));
    printf("sizeof(a + b): %zu bytes\n\n", size_of_result);
    // Output demonstrates size_of_result == sizeof(int) (typically 4), NOT sizeof(char) (1).

    unsigned char c = 0xAA; // 1010 1010 in binary

    // 1. 'c' is promoted to int: 0x000000AA (assuming 32-bit int)
    // 2. Bitwise NOT (~) is applied to the 32-bit int.
    // 3. The result is 0xFFFFFF55, NOT 0x55.
    int result = ~c; 

    // To restrict the result back to the original type width, 
    // an explicit cast is required after the operation.
    unsigned char truncated_result = (unsigned char)(~c); // Yields 0x55

    printf("Original c:   0x%X\n", c);
    printf("Promoted ~c:  0x%X\n", (unsigned int)result);
    printf("Truncated ~c: 0x%X\n", truncated_result);

    return 0;
}

sizeof(char): 1 byte(s)
sizeof(a + b): 4 bytes

Original c:   0xAA
Promoted ~c:  0xFFFFFF55
Truncated ~c: 0x55