Question

(In c code only, not c++)

We will simulate the status of 8 LEDs that are connected to a microcontroller. Assume that the state of each LED (ON or OFF) is determined by each of the bits (1 or 0) in an 8-bit register (high-speed memory).

1. Declare a char variable called led_reg and initialize it to 0.
   Assume that the least-significant bit (lsb) controls LED#0 and the most-significant bit (msb) controls LED#7.
   
2. In the main function, build and present a menu to the user and enclose it in a loop that ends when the Quit option is chosen. Use if-else or switch-case statements to implement the operations described:
   
   Menu:
   0. Turn ON LED#4
   1. Turn OFF LED#4
   2. Add 1 to the LED Register
   3. Turn ON all the even numbered LEDs
   4. Turn OFF all the even numbered LEDs
   5. Toggle the state of LED#3.
   6. Shift the values of the LED Register right by 1
   7. Quit
   
3. Create a function called: printBinary() with the following properties:
   
   • one input argument of type char
   • returns nothing
   • prints the binary representation (in 8-bits) of the char input value.
   
4. Use the printBinary() function to display the value of the LED register before the menu.

HINTS:

• Each operation can be performed with a single expression (line of code).
• Append 0b or 0x to numerical constants to denote binary or hexadecimal values in source code, respectively.
  10101010₂ = 0b10101010
  FF₁₆ = 0xFF

Answer 1

Here is the code:

#include <stdio.h>

void printBinary (unsigned char ch) {
    int i, digit[8];
    
    printf ("0b");
    for (i = 0; i < 8; i++) {
        digit[i] = (ch % 2 == 0 ? 0 : 1);
        ch = ch >> 1;
    }
    for (i = 7; i >= 0; i--)
            printf ("%d", digit[i]);
    printf ("\n");
    
}

int main()
{
    unsigned char led_reg = 0;
    int menu_choice = -1;
    
    printBinary (led_reg);
    while (menu_choice != 7) {
        printf ("Menu:\n");
        printf ("0. Turn ON LED#4\n");
        printf ("1. Turn OFF LED#4\n");
        printf ("2. Add 1 to the LED Register\n");
        printf ("3. Turn ON all the even numbered LEDs\n");
        printf ("4. Turn OFF all the even numbered LEDs\n");
        printf ("5. Toggle the state of LED#3.\n");
        printf ("6. Shift the values of the LED Register right by 1\n");
        printf ("7. Quit\n");
        scanf ("%d[^\n]\n", &menu_choice);
        switch (menu_choice) {
            case 0:
                led_reg |= (1 << 4);
                printBinary (led_reg);
                break;
            case 1:
                led_reg &= (0 << 4);
                printBinary (led_reg);
                break;
            case 2:
                led_reg += 1;
                break;
            case 3:
                led_reg = led_reg | 0x55; // alternate bits set
                printBinary (led_reg);
                break;
            case 4:
                led_reg = led_reg & 0xAA;
                printBinary (led_reg);
                break;
            case 5:
                led_reg = (led_reg & 0x8) ? (led_reg & ~(0x8)) : (led_reg | 0x8);
                printBinary (led_reg);
                break;
            case 6:
                led_reg = (led_reg >> 1);
                printBinary (led_reg);
                break;
                
        }
    }
    return 0;
}