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Check whether the bit at given position is set or unset
  • Difficulty Level : Medium
  • Last Updated : 09 Nov, 2020

Given two positive integers n and k. The problem is to check whether the bit at position k from the right in the binary representation of n is set (‘1’) or unset (‘0’).
Constraints: 1 <= k <= number of bits in the binary representation of n.

Examples:

Input : n = 10, k = 2
Output : Set
(10)10 = (1010)2
The 2nd bit from the right is set.

Input : n = 21, k = 4
Output : Unset

Approach: Following are the steps:

  1. Calculate new_num = (n >> (k – 1)).
  2. if (new_num & 1) == 1 then bit is “Set”, else “Unset”.

C++

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// C++ implementation to check whether the bit
// at given position is set or unset
#include <bits/stdc++.h>
using namespace std;
  
// function to check whether the bit
// at given position is set or unset
bool bitAtGivenPosSetOrUnset(unsigned int n,
                             unsigned int k)
{
    int new_num = n >> (k - 1);
  
    // if it results to '1' then bit is set,
    // else it results to '0' bit is unset
    return (new_num & 1);
}
  
// Driver program to test above
int main()
{
    unsigned int n = 10, k = 2;
    if (bitAtGivenPosSetOrUnset(n, k))
        cout << "Set";
    else
        cout << "Unset";
    return 0;
}

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Java

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// Java program to
// check the set bit
// at kth position
import java.io.*;
  
class GFG {
      
// function to check whether
// the bit at given position
// is set or unset
static int bitAtGivenPosSetOrUnset
                   ( int n, int k)
{
  
    // to shift the kth bit
    // at 1st position
    int new_num = n >> (k - 1);
   
    // Since, last bit is now 
    // kth bit, so doing AND with 1
    // will give result.
    return (new_num & 1);
}
    public static void main (String[] args)
    {
         // K and n must be greater than 0
         int n = 10, k = 2;
           
    if (bitAtGivenPosSetOrUnset(n, k)==1)
        System.out.println("Set");
    else
        System.out.println("Unset");
    }
}
  
//This code is contributed by Gitanjali

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Python3

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# python implementation to check
# whether the bit at given
# position is set or unset
  
import math
#function to check whether the bit
# at given position is set or unset
def bitAtGivenPosSetOrUnset(  n,  k):
     new_num = n >> (k - 1)
   
     #if it results to '1' then bit is set,
     #else it results to '0' bit is unset
     return (new_num & 1)
  
# Driver code
n = 10
k = 2
if (bitAtGivenPosSetOrUnset(n, k)):
     print("Set")
else:
    print("Unset")
  
#This code is contributed by Gitanjali

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C#

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// C# program to check the set bit
// at kth position
using System;
  
class GFG {
      
    // function to check whether
    // the bit at given position
    // is set or unset
    static int bitAtGivenPosSetOrUnset(
                           int n, int k)
    {
      
        // to shift the kth bit
        // at 1st position
        int new_num = n >> (k - 1);
      
        // Since, last bit is now 
        // kth bit, so doing AND with 1
        // will give result.
        return (new_num & 1);
    }
      
    // Driver code
    public static void Main ()
    {
          
        // K and n must be greater 
        // than 0
        int n = 10, k = 2;
          
        if (bitAtGivenPosSetOrUnset(n, k)==1)
            Console.Write("Set");
        else
            Console.Write("Unset");
    }
}
  
// This code is contributed by Sam007.

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PHP

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<?php
// PHP implementation to check whether the bit
// at given position is set or unset
  
// function to check whether the bit
// at given position is set or unset
function bitAtGivenPosSetOrUnset($n, $k)
{
    $new_num = $n >> ($k - 1);
  
    // if it results to '1' then bit is set,
    // else it results to '0' bit is unset
    return ($new_num & 1);
}
  
    // Driver Code
    $n = 10;
    $k = 2;
    if (bitAtGivenPosSetOrUnset($n, $k))
        echo "Set";
    else
        echo "Unset";
          
// This code is contributed by Sam007
?>

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Output:

Set

Time Complexity: O(1).

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