Web and Mobile Apps Dev

This is the continuation of the C programming tutorial series from the last post which I wrote Dec 7 of last year.

The shift-left operator (<<, or double left) is used to shift the bit pattern of a number by a certain number of bits to the left.

The shift-right operator (>>, or double right) is used to shift this bit pattern to the opposite direction (right).

For example, the bit pattern of five (5) is 101. The result bit pattern of shifting it 4 bits to the left is 1010000.

If shifting left are too far such as 50, it will produce undefined results, while right shifting too far will simply be truncated.

Here is an example of shift-left operator:

13<<3=104
 13 (00001101)
104 (01101000)

The bit pattern between 13 and 104 is exactly shifted left 3 places.

Notice the division of 104 and 13 is exactly 8, which is 2 to the power of 3, which means

13*2^3=104

which is almost the same as the above statement with shift-left operator.

Here is another example for the shift-right operator:

52>>4=3
52 (00110100)
 3 (00000011)

The bit pattern between 52 and 3 is shifted right 4 spaces, which removed the last 4 digit (0100) which is the reminder of 3.

This is exactly the same as the last example except this one is divide by 2 to the power of 4:

52 / 2^4 = 3

Note that this is integer division, therefore there is no remainder or decimal.

Based on the above examples, you can see that shifting left is multiply by 2 and sifting right is divide by 2.

Below is the example code for the shift operators:

/*
 * shift.c
 *
 * Program to demonstrate the shift left and right operators
 *
 * by Mark Virtue, 2001.
 *
 */

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

 static void goodbye() {
 	while (getchar() != 'n') {};
 	printf("nPress ENTER to exit: ");
 	fflush(stdin);
 	getchar();
 }

 main() {
 	unsigned int number;
 	int shift;
 	unsigned int result;

 	atexit(goodbye);

 	printf("Please enter a number: ");
 	scanf("%d", &number);
 	printf("How many bits would you like to shift (negative to shift right)? ");
 	scanf("%d", &shift);

 	if (shift >= 0) {
 		result = number << shift;
 	}
 	else {
 		result = number >> -shift;
 	}

 	printf("%u (hex %X) shifted %s %d is %u (hex %X)n",
 		number, number,
 		shift >= 0 ? "left" : "right",
 		shift >= 0 ? shift : -shift,
 		result, result);

 	return 0;
 }

If you have any issue compiling the above code or any question regarding this post, leave a comment below and I will help you ASAP.