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Toggle all bits after most significant bit
• Difficulty Level : Hard
• Last Updated : 21 Jun, 2018

Given a number, toggle all bits of it after most significant bit including most significant bit.

Examples :

```Input : 10
Output : 5
Binary representation of 10 is 1010
After toggling we get 0101

Input : 5
Output : 2
```

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

We can toggle a bit by doing XOR of it with 1 (Note that 1 ^ 0 = 1 and 1 ^ 1 = 0). The idea is to take a number temp with only one bit set. One by one move the only set bit of temp to left and do XOR of it with n until it crosses MSB (Most Significant Bit) of n.

## C++

 `// CPP program to toggle set  bits starting  ` `// from MSB ` `#include ` `using` `namespace` `std; ` ` `  `void` `toggle(``int` `&n) ` `{ ` `    ``// temporary variable to ` `    ``// use XOR with one of a n ` `    ``int` `temp = 1; ` ` `  `    ``// Run loop until the only ` `    ``// set bit in temp crosses ` `    ``// MST of n. ` `    ``while` `(temp <= n) ` `    ``{ ` `        ``// Toggle bit of n ` `        ``// corresponding to ` `        ``// current set bit in ` `        ``// temp. ` `        ``n = n ^ temp; ` ` `  `        ``// Move set bit to next ` `        ``// higher position. ` `        ``temp = temp << 1; ` `    ``} ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 10; ` `    ``toggle(n); ` `    ``cout << n; ` `    ``return` `0; ` `} `

## Java

 `// Java program to toggle set  ` `// bits starting from MSB ` ` `  `class` `GFG { ` `     `  `static` `int` `toggle(``int` `n) { ` `     `  `    ``// temporary variable to ` `    ``// use XOR with one of a n ` `    ``int` `temp = ``1``; ` ` `  `    ``// Run loop until the only ` `    ``// set bit in temp crosses ` `    ``// MST of n. ` `    ``while` `(temp <= n) { ` `         `  `    ``// Toggle bit of n ` `    ``// corresponding to ` `    ``// current set bit in ` `    ``// temp. ` `    ``n = n ^ temp; ` ` `  `    ``// Move set bit to next ` `    ``// higher position. ` `    ``temp = temp << ``1``; ` `    ``} ` `    ``return` `n; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String arg[])  ` `{ ` `    ``int` `n = ``10``; ` `    ``n = toggle(n); ` `    ``System.out.print(n); ` `} ` `} ` ` `  `// This code is contributed by Anant Agarwal. `

## Python3

 `# Python program to toggle ` `# set  bits starting  ` `# from MSB ` ` `  `def` `toggle(n): ` ` `  `    ``# temporary variable to ` `    ``# use XOR with one of a n ` `    ``temp ``=` `1` `  `  `    ``#Run loop until the only ` `    ``#set bit in temp crosses ` `    ``#MST of n. ` `    ``while` `(temp <``=` `n): ` `     `  `        ``# Toggle bit of n ` `        ``# corresponding to ` `        ``# current set bit in ` `        ``# temp. ` `        ``n ``=` `n ^ temp ` `  `  `        ``# Move set bit to next ` `        ``# higher position. ` `        ``temp ``=` `temp << ``1` ` `  `    ``return` `n ` `  `  `# Driver code ` ` `  `n ``=` `10` `n``=``toggle(n) ` `print``(n) ` ` `  `# This code is contributed ` `# by Anant Agarwal. `

## C#

 `// C# program to toggle set  ` `// bits starting from MSB ` `using` `System; ` ` `  `class` `GFG { ` ` `  `// Function to toggle bits ` `// starting from MSB     ` `static` `int` `toggle(``int` `n) { ` `     `  `    ``// temporary variable to ` `    ``// use XOR with one of a n ` `    ``int` `temp = 1; ` ` `  `    ``// Run loop until the only ` `    ``// set bit in temp crosses ` `    ``// MST of n. ` `    ``while` `(temp <= n) { ` `         `  `    ``// Toggle bit of n ` `    ``// corresponding to ` `    ``// current set bit in ` `    ``// temp. ` `    ``n = n ^ temp; ` ` `  `    ``// Move set bit to next ` `    ``// higher position. ` `    ``temp = temp << 1; ` `    ``} ` `    ``return` `n; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main()  ` `{ ` `    ``int` `n = 10; ` `    ``n = toggle(n); ` `    ``Console.Write(n); ` `} ` `} ` ` `  `// This code is contributed by Nitin Mittal. `

## PHP

 ` `

Output :

`5`

The above solution can be optimized to work in O(1) time under the assumption that numbers are stored in 32 bits.

## C++

 `// CPP program to toggle set  bits starting  ` `// from MSB ` `#include ` `using` `namespace` `std; ` ` `  `// Returns a number which has all set bits ` `// starting from MSB of n ` `int` `setAllBitsAfterMSB(``int` `n) ` `{     ` `    ``// This makes sure two bits ` `    ``// (From MSB and including MSB) ` `    ``// are set ` `    ``n |= n>>1; ` ` `  `    ``// This makes sure 4 bits ` `    ``// (From MSB and including MSB) ` `    ``// are set ` `    ``n |= n>>2;    ` ` `  `    ``n |= n>>4;   ` `    ``n |= n>>8; ` `    ``n |= n>>16; ` `    ``return` `n; ` `} ` ` `  `void` `toggle(``int` `&n) ` `{ ` `    ``n = n ^ setAllBitsAfterMSB(n); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 10; ` `    ``toggle(n); ` `    ``cout << n; ` `    ``return` `0; ` `} `

## Java

 `// Java program to toggle set bits  ` `// starting from MSB ` ` `  `class` `GFG { ` `     `  `// Returns a number which has all  ` `// set bits starting from MSB of n ` `static` `int` `setAllBitsAfterMSB(``int` `n) { ` `     `  `    ``// This makes sure two bits ` `    ``// (From MSB and including MSB) ` `    ``// are set ` `    ``n |= n >> ``1``; ` ` `  `    ``// This makes sure 4 bits ` `    ``// (From MSB and including MSB) ` `    ``// are set ` `    ``n |= n >> ``2``; ` ` `  `    ``n |= n >> ``4``; ` `    ``n |= n >> ``8``; ` `    ``n |= n >> ``16``; ` `    ``return` `n; ` `} ` `static` `int` `toggle(``int` `n)  ` `{ ` `    ``n = n ^ setAllBitsAfterMSB(n); ` `    ``return` `n; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String arg[])  ` `{ ` `    ``int` `n = ``10``; ` `    ``n = toggle(n); ` `    ``System.out.print(n); ` `} ` `} ` ` `  `// This code is contributed by Anant Agarwal. `

## Python3

 `# Python program to toggle set  bits starting  ` `# from MSB ` ` `  `# Returns a number which has all set bits ` `# starting from MSB of n ` `def` `setAllBitsAfterMSB(n): ` `  `  `    ``# This makes sure two bits ` `    ``# (From MSB and including MSB) ` `    ``# are set ` `    ``n |``=` `n>>``1` `  `  `    ``# This makes sure 4 bits ` `    ``# (From MSB and including MSB) ` `    ``# are set ` `    ``n |``=` `n>>``2`    `  `  `    ``n |``=` `n>>``4`   `    ``n |``=` `n>>``8` `    ``n |``=` `n>>``16` `    ``return` `n ` ` `  `def` `toggle(n): ` ` `  `    ``n ``=` `n ^ setAllBitsAfterMSB(n) ` `    ``return` `n ` `     `  `#Driver code ` ` `  `n ``=` `10` `n``=``toggle(n) ` `print``(n) ` `# This code is contributed by Anant Agarwal. `

## C#

 `// C# program to toggle set bits  ` `// starting from MSB ` `using` `System; ` ` `  `class` `GFG { ` `         `  `    ``// Returns a number which has all  ` `    ``// set bits starting from MSB of n ` `    ``static` `int` `setAllBitsAfterMSB(``int` `n) ` `    ``{ ` `         `  `        ``// This makes sure two bits ` `        ``// (From MSB and including MSB) ` `        ``// are set ` `        ``n |= n >> 1; ` `     `  `        ``// This makes sure 4 bits ` `        ``// (From MSB and including MSB) ` `        ``// are set ` `        ``n |= n >> 2; ` `     `  `        ``n |= n >> 4; ` `        ``n |= n >> 8; ` `        ``n |= n >> 16; ` `        ``return` `n; ` `    ``} ` `     `  `    ``static` `int` `toggle(``int` `n)  ` `    ``{ ` `        ``n = n ^ setAllBitsAfterMSB(n); ` `        ``return` `n; ` `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `Main()  ` `    ``{ ` `        ``int` `n = 10; ` `        ``n = toggle(n); ` `        ``Console.WriteLine(n); ` `    ``} ` `} ` ` `  `// This code is contributed by Sam007. `

## PHP

 `> 1; ` ` `  `    ``// This makes sure 4 bits ` `    ``// (From MSB and including MSB) ` `    ``// are set ` `    ``\$n` `|= ``\$n` `>> 2;  ` ` `  `    ``\$n` `|= ``\$n` `>> 4;  ` `    ``\$n` `|= ``\$n` `>> 8; ` `    ``\$n` `|= ``\$n` `>> 16; ` `    ``return` `\$n``; ` `} ` `function` `toggle(&``\$n``) ` `{ ` `    ``\$n` `= ``\$n` `^ setAllBitsAfterMSB(``\$n``); ` `} ` ` `  `// Driver Code ` `\$n` `= 10; ` `toggle(``\$n``); ` `echo` `\$n``; ` ` `  `// This code is contributed by ajit ` `?> `

Output :

`5`

Thanks to Devanshu Agarwal for suggesting this approach.

This article is contributed by Devanshu Agarwal. 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.