A nibble is a four-bit aggregation, or half an octet. There are two nibbles in a byte.

Given a byte, swap the two nibbles in it. For example 100 is be represented as 01100100 in a byte (or 8 bits). The two nibbles are (0110) and (0100). If we swap the two nibbles, we get 01000110 which is 70 in decimal.

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To swap the nibbles, we can use bitwise &, bitwise ‘<<' and '>>’ operators. A byte can be represented using a unsigned char in C as size of char is 1 byte in a typical C compiler. Following is C program to swap the two nibbles in a byte.

#include <stdio.h> unsigned char swapNibbles(unsigned char x) { return ( (x & 0x0F)<<4 | (x & 0xF0)>>4 ); } int main() { unsigned char x = 100; printf("%u", swapNibbles(x)); return 0; }

Output:

70

**Explanation:**

100 is 01100100 in binary. The operation can be split mainly in two parts

**1)** The expression “**x & 0x0F**” gives us last 4 bits of x. For x = 100, the result is 00000100. Using bitwise ‘<<' operator, we shift the last four bits to the left 4 times and make the new last four bits as 0. The result after shift is 01000000.
**2)** The expression “**x & 0xF0**” gives us first four bits of x. For x = 100, the result is 01100000. Using bitwise ‘>>’ operator, we shift the digit to the right 4 times and make the first four bits as 0. The result after shift is 00000110.

At the end we use the bitwise OR ‘|’ operation of the two expressions explained above. The OR operator places first nibble to the end and last nibble to first. For x = 100, the value of (01000000) OR (00000110) gives the result 01000110 which is equal to 70 in decimal.

This article is contributed by **Anuj Garg**. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above