Set, Clear and Toggle a given bit of a number in C - GeeksforGeeks

20 Nov, 2019
Given a number N, the task is to set, clear and toggle the K-th bit of this number N.
Setting a bit means that if K-th bit is 0, then set it to 1 and if it is 1 then leave it unchanged.
Clearing a bit means that if K-th bit is 1, then clear it to 0 and if it is 0 then leave it unchanged.
Toggling a bit means that if K-th bit is 1, then change it to 0 and if it is 0 then change it to 1.
Examples:
Input: N = 5, K = 1
Output: 
Setting Kth bit: 5
Clearing Kth bit: 4
Toggling Kth bit: 4
Explanation: 
5 is represented as 101 in binary
and has its first bit 1, so 
setting it will result in 101 i.e. 5.
clearing it will result in 100 i.e. 4.
toggling it will result in 100 i.e. 4.

Input: N = 7, K = 2
Output: 
Setting Kth bit: 7
Clearing Kth bit: 5
Toggling Kth bit: 5
Explanation: 
7 is represented as 111 in binary
and has its second bit 1, so 
setting it will result in 111 i.e. 7.
clearing it will result in 101 i.e. 5.
toggling it will result in 101 i.e. 5.

Approach:
Below are the steps to set, clear and toggle Kth bit of N:
Setting a bit
Since we all know that performing bitwise OR of any bit with a set bit results in a set bit, i.e.Any bit <bitwise OR> Set bit = Set bit

which means,
0 | 1 = 1
1 | 1 = 1

Any bit <bitwise OR> Set bit = Set bit

which means,
0 | 1 = 1
1 | 1 = 1

So for setting a bit, performing a bitwise OR of the number with a set bit is the best idea.N = N | 1 << K
OR
N |= 1 << K

where K is the bit that is to be set

N = N | 1 << K
OR
N |= 1 << K

where K is the bit that is to be set

Clearing a bit
Since bitwise AND of any bit with a reset bit results in a reset bit, i.e.Any bit <bitwise AND> Reset bit = Reset bit

which means,
0 & 0 = 0
1 & 0 = 0


    So for clearing a bit, performing a bitwise AND of the number with a reset bit is the best idea.

n = n & ~(1 << k)
OR
n &= ~(1 << k)

where k is the bit that is to be cleared

Any bit <bitwise AND> Reset bit = Reset bit

which means,
0 & 0 = 0
1 & 0 = 0


    So for clearing a bit, performing a bitwise AND of the number with a reset bit is the best idea.

n = n & ~(1 << k)
OR
n &= ~(1 << k)

where k is the bit that is to be cleared



    So for clearing a bit, performing a bitwise AND of the number with a reset bit is the best idea.

n = n & ~(1 << k)
OR
n &= ~(1 << k)

where k is the bit that is to be cleared

So for clearing a bit, performing a bitwise AND of the number with a reset bit is the best idea.

n = n & ~(1 << k)
OR
n &= ~(1 << k)

where k is the bit that is to be cleared

n = n & ~(1 << k)
OR
n &= ~(1 << k)

where k is the bit that is to be cleared

Toggle a bit
Since XOR of unset and set bit results in a set bit and XOR of a set and set bit results in an unset bit. Hence performing bitwise XOR of any bit with a set bit results in toggle of that bit, i.e.Any bit <bitwise XOR> Set bit = Toggle

which means,
0 ^ 1 = 1
1 ^ 1 = 0


    So in order to toggle a bit, performing a bitwise XOR of the number with a reset bit is the best idea.

n = n ^ 1 << k
OR
n ^= 1 << k

where k is the bit that is to be cleared

Any bit <bitwise XOR> Set bit = Toggle

which means,
0 ^ 1 = 1
1 ^ 1 = 0


    So in order to toggle a bit, performing a bitwise XOR of the number with a reset bit is the best idea.

n = n ^ 1 << k
OR
n ^= 1 << k

where k is the bit that is to be cleared



    So in order to toggle a bit, performing a bitwise XOR of the number with a reset bit is the best idea.

n = n ^ 1 << k
OR
n ^= 1 << k

where k is the bit that is to be cleared

So in order to toggle a bit, performing a bitwise XOR of the number with a reset bit is the best idea.

n = n ^ 1 << k
OR
n ^= 1 << k

where k is the bit that is to be cleared

n = n ^ 1 << k
OR
n ^= 1 << k

where k is the bit that is to be cleared

Below is the implementation of the above approach:
// C program to set, clear and toggle a bit  #include <stdio.h>  // Function to set the kth bit of nint setBit(int n, int k){    return (n | (1 << (k - 1)));}  // Function to clear the kth bit of nint clearBit(int n, int k){    return (n & (~(1 << (k - 1))));}  // Function to toggle the kth bit of nint toggleBit(int n, int k){    return (n ^ (1 << (k - 1)));}  // Driver codeint main(){    int n = 5, k = 1;      printf("%d with %d-th bit Set: %d\n",           n, k, setBit(n, k));    printf("%d with %d-th bit Cleared: %d\n",           n, k, clearBit(n, k));    printf("%d with %d-th bit Toggled: %d\n",           n, k, toggleBit(n, k));    return 0;}
5 with 1-th bit Set: 5
5 with 1-th bit Cleared: 4
5 with 1-th bit Toggled: 4

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