Program to set Nth bit of a number in C++

Written by

Garvit Gulati

Given a number num and a value n, we have to set the value of nth bit from right in the binary representation of that number.

Introduction to Left shift and Right shift operator

  • The left shift and right shift operators are used to shift the bits of a number either left or right as specified.
  • RIGHT SHIFT(>>): it accepts to numbers, and shifts the first number to the right, number of times as specified by the second number. For example,
  • Shifting a number to left n times, is equivalent to multiplying the number by 2n.

# Approaching the problem

Setting nth bit of a number means assigning the value 1 to its nth bit if it was 0 and if 1 leaving it as it is.

To set the nth bit of  a number we have to operate it with a number such that it edits only the nth bit of that number.

Since we have to turn it to 1 if its zero and leave it as it is if its 1, its clear that we have to perform an OR operation with a number that has 1 at the nth bit. Rest of the bits should be zero so that it doesn’t change any other bit. The number will be obtained by shifting 1 to the right by n-1 times.

For example, we have to set 2nd bit 13

13 1 1 0 1
1>>(n-1) 0 0 1 0
OR 1 1 1 1 =15

# Algorithm

  1. The user is prompted to enter an integer value, which is stored in the num variable.
  2. The user is then prompted to enter the position of the bit they wish to set, which is stored in the n variable.
  3. A bitwise OR operation is performed between num and a value that has a single bit set at the nth position. This is done by shifting the value 1 to the left by n-1 bits using the << operator and using the OR operator (|) to set the nth bit of num.
  4. The result of the OR operation is printed to the console.


#include <iostream>
using namespace std;

int main()
    int num, n;

    cout << "Enter number: ";
    cin >> num;

    cout << "Enter bit number you wish to set: ";
    cin >> n;

    cout << "Bit set Successfully" << endl;
    cout << "Answer: " << (num | (1 << (n - 1))) << endl;

    return 0;


Enter Number

Enter bit number you wish to set

Bit set Successfully
Answer: 15
Program to set Nth bit of a number in C++