# Unset the last m bits

Given a non-negative number n. The problem is to unset the last m bits in the binary representation of n.

Constraint: 1 <= m <= num, where num is the number of bits in the binary representation of n.

Examples:

```Input : n = 10, m = 2
Output : 8
(10)10 = (1010)2
(8)10 = (1000)2
The last two bits in the binary
representation of 10 have been unset.

Input : n = 150, m = 4
Output : 144
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Following are the steps:

1. Calculate num = (1 << (sizeof(int) * 8 – 1)) – 1. This will produce the highest positive integer num. All the bits in num will be set.
2. Toggle the last m bits in num. Refer this post.
3. Now, perform n = n & num. This will unset the last m bits in n.
4. Return n.

Note: The sizeof(int) has been used as input is of int data type. For large inputs you can use long int or long long int datatypes in place of int.

## C++

 `// C++ implementation to unset bits the last m bits ` `#include ` `using` `namespace` `std; ` ` `  `// function to toggle the last m bits ` `unsigned ``int` `toggleLastMBits(unsigned ``int` `n, ` `                             ``unsigned ``int` `m) ` `{ ` `    ``// calculating a number 'num' having 'm' bits ` `    ``// and all are set ` `    ``unsigned ``int` `num = (1 << m) - 1; ` ` `  `    ``// toggle the last m bits and return the number ` `    ``return` `(n ^ num); ` `} ` ` `  `// function to unset bits the last m bits ` `unsigned ``int` `unsetLastMBits(unsigned ``int` `n, ` `                            ``unsigned ``int` `m) ` `{ ` `    ``// 'num' is the highest positive integer number ` `    ``// all the bits of 'num' are set ` `    ``unsigned ``int` `num = (1 << (``sizeof``(``int``) * 8 - 1)) - 1; ` ` `  `    ``// toggle the last 'm' bits in 'num' ` `    ``num = toggleLastMBits(num, m); ` ` `  `    ``// unset the last 'm' bits in 'n' ` `    ``// and return the number ` `    ``return` `(n & num); ` `} ` ` `  `// Driver program to test above ` `int` `main() ` `{ ` `    ``unsigned ``int` `n = 150, m = 4; ` `    ``cout << unsetLastMBits(n, m); ` `    ``return` `0; ` `} `

## Java

 `// Java implementation to unset ` `// bits the last m bits ` `class` `GFG  ` `{ ` `     `  `static` `int` `sizeofInt = ``8``; ` ` `  `// function to toggle the last m bits ` `static` `int` `toggleLastMBits(``int` `n, ` `                            ``int` `m) ` `{ ` `    ``// calculating a number 'num' having 'm' bits ` `    ``// and all are set ` `    ``int` `num = (``1` `<< m) - ``1``; ` ` `  `    ``// toggle the last m bits and return the number ` `    ``return` `(n ^ num); ` `} ` ` `  `// function to unset bits the last m bits ` `static` `int` `unsetLastMBits(``int` `n, ` `                            ``int` `m) ` `{ ` `    ``// 'num' is the highest positive integer number ` `    ``// all the bits of 'num' are set ` `    ``int` `num = (``1` `<< (sizeofInt * ``8` `- ``1``)) - ``1``; ` ` `  `    ``// toggle the last 'm' bits in 'num' ` `    ``num = toggleLastMBits(num, m); ` ` `  `    ``// unset the last 'm' bits in 'n' ` `    ``// and return the number ` `    ``return` `(n & num); ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``int` `n = ``150``, m = ``4``; ` `    ``System.out.println(unsetLastMBits(n, m)); ` `} ` `} ` ` `  `/* This code contributed by PrinciRaj1992 */`

## Python3

 `# Python3 implementation to unset ` `# bits the last m bits ` `import` `sys ` ` `  `# function to toggle the last m bits ` `def` `toggleLastMBits (n, m): ` `     `  `    ``# calculating a number 'num'  ` `    ``# having 'm' bits and all are set ` `    ``num ``=` `(``1` `<< m) ``-` `1` ` `  `    ``# toggle the last m bits ` `    ``# and return the number ` `    ``return` `(n ^ num) ` ` `  `# function to unset bits ` `# the last m bits ` `def` `unsetLastMBits(n, m): ` ` `  `    ``# 'num' is the highest positive integer  ` `    ``# number all the bits of 'num' are set ` `    ``num ``=` `(``1` `<< (sys.getsizeof(``int``) ``*` `8` `-` `1``)) ``-` `1` ` `  `    ``# toggle the last 'm' bits in 'num' ` `    ``num ``=` `toggleLastMBits(num, m) ` ` `  `    ``# unset the last 'm' bits in 'n' ` `    ``# and return the number ` `    ``return` `(n & num) ` ` `  `# Driven code ` `n ``=` `150` `m ``=` `4` `print` `(unsetLastMBits(n, m)) ` ` `  `# This code is contributed by "rishabh_jain". `

## C#

 `// C# implementation to unset  ` `// bits the last m bits  ` `using` `System; ` ` `  `class` `GFG  ` `{  ` `     `  `static` `int` `sizeofInt = 8;  ` ` `  `// function to toggle the last m bits  ` `static` `int` `toggleLastMBits(``int` `n,  ` `                            ``int` `m)  ` `{  ` `    ``// calculating a number 'num' having 'm' bits  ` `    ``// and all are set  ` `    ``int` `num = (1 << m) - 1;  ` ` `  `    ``// toggle the last m bits and return the number  ` `    ``return` `(n ^ num);  ` `}  ` ` `  `// function to unset bits the last m bits  ` `static` `int` `unsetLastMBits(``int` `n,  ` `                            ``int` `m)  ` `{  ` `    ``// 'num' is the highest positive integer number  ` `    ``// all the bits of 'num' are set  ` `    ``int` `num = (1 << (sizeofInt * 8 - 1)) - 1;  ` ` `  `    ``// toggle the last 'm' bits in 'num'  ` `    ``num = toggleLastMBits(num, m);  ` ` `  `    ``// unset the last 'm' bits in 'n'  ` `    ``// and return the number  ` `    ``return` `(n & num);  ` `}  ` ` `  `// Driver code  ` `public` `static` `void` `Main(String[] args)  ` `{  ` `    ``int` `n = 150, m = 4;  ` `    ``Console.WriteLine(unsetLastMBits(n, m));  ` `}  ` `}  ` ` `  `// This code contributed by Rajput-Ji `

## PHP

 ` `

Output:

```144
```

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Article Tags :
Practice Tags :

Be the First to upvote.

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.