C - Bitwise AND assignment operator

The Bitwise AND assignment operator (&=) assigns the first operand a value equal to the result of Bitwise AND operation of two operands.

(x &= y) is equivalent to (x = x & y)

The Bitwise AND operator (&) is a binary operator which takes two bit patterns of equal length and performs the logical AND operation on each pair of corresponding bits. It returns 1 if both bits at the same position are 1, else returns 0.

The example below describes how bitwise AND operator works:

50 & 25 returns 16

     50    ->    110010  (In Binary)
   & 25    ->  & 011001  (In Binary)
    ----        --------
     16    <-    010000  (In Binary)  

The code of using Bitwise AND assignment operator (&=) is given below:

#include <stdio.h>
 
int main (){
  int x = 50;
  int y = 25;

  //Bitwise AND assignment operation
  x &= y;

  //Displaying the result
  printf("x = %d\n", x);
  return 0;
}

The output of the above code will be:

x = 16

Example: Check if a number is even or odd

The last bit of an even number is always 0, whereas for an odd number the last bit is always 1. Therefore, for a given number n, (n & 1) returns 0 if the n is even, else returns 1.

Even Number: 

     50   ->    110010  (In Binary)
    & 1   ->  & 000001  (In Binary)
    ----       --------
      0   <-    000000

Odd Number: 

     99   ->    1100011  (In Binary)
    & 1   ->  & 0000001  (In Binary)
    ----       ---------
      1   <-    0000001

The below code checks whether a given number is even or odd:

#include <stdio.h>

static void CheckEven(int MyNum){
  int x = MyNum;
  x &= 1;
  if (x == 1){
    printf("%d is an odd number.\n", MyNum);
  } else {
    printf("%d is an even number.\n", MyNum);
  }
}

int main() {
  CheckEven(50);
  CheckEven(99);
  return 0;
}

The above code will give the following output:

50 is an even number.
99 is an odd number.