# Set all even bits of a number

Given a number, the task is to set all even bit of a number. Positions of bits are counted from LSB (least significant bit) to MSB (Most significant bit). Position of LSB is considered as 1.

Examples :

```Input : 20
Output : 30
Binary representation of 20 is
10100. After setting
even bits, we get 11110

Input : 10
Output : 10
```

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

Method 1:-
1. First generate a number that contains even position bits.
2. Take OR with the original number. Note that 1 | 1 = 1 and 1 | 0 = 1.

Let’s understand this approach with below code.

## C++

 `// Simple CPP program to set all even ` `// bits of a number ` `#include ` `using` `namespace` `std; ` ` `  `// Sets even bits of n and returns  ` `// modified number. ` `int` `evenbitsetnumber(``int` `n) ` `{ ` `    ``// Generate 101010...10 number and ` `    ``// store in res. ` `    ``int` `count = 0, res = 0; ` `    ``for` `(``int` `temp = n; temp > 0; temp >>= 1) { ` ` `  `        ``// if bit is even then generate ` `        ``// number and or with res ` `        ``if` `(count % 2 == 1) ` `            ``res |= (1 << count); ` ` `  `        ``count++; ` `    ``} ` ` `  `    ``// return OR number ` `    ``return` `(n | res); ` `} ` ` `  `int` `main() ` `{ ` `    ``int` `n = 10; ` `    ``cout << evenbitsetnumber(n); ` `    ``return` `0; ` `} `

## Java

 `// Simple Java program to set all even ` `// bits of a number ` `class` `GFG  ` `{ ` `    ``// Sets even bits of n and returns  ` `    ``// modified number. ` `    ``static` `int` `evenbitsetnumber(``int` `n) ` `    ``{ ` `        ``// Generate 101010...10 number and ` `        ``// store in res. ` `        ``int` `count = ``0``, res = ``0``; ` `        ``for` `(``int` `temp = n; temp > ``0``; temp >>= ``1``) { ` `            `  `            ``// if bit is even then generate ` `            ``// number and or with res ` `            ``if` `(count % ``2` `== ``1``) ` `            ``res |= (``1` `<< count); ` ` `  `        ``count++; ` `        ``} ` `         `  `        ``// return OR number ` `        ``return` `(n | res); ` `         `  `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``int` `n = ``4``; ` `         ``System.out.println(evenbitsetnumber(n)); ` `    ``} ` `} ` ` `  `// This code is contributed  ` `// by  prerna saini.  `

## Python3

 `# Simple Python program to set all even ` `# bits of a number ` ` `  `# Sets even bits of n and returns  ` `# modified number. ` `def` `evenbitsetnumber(n): ` ` `  `    ``# Generate 101010...10 number and ` `    ``# store in res. ` `    ``count ``=` `0` `    ``res ``=` `0` `    ``temp ``=` `n ` `    ``while``(temp > ``0``): ` ` `  `        ``# if bit is even then generate ` `        ``# number and or with res ` `        ``if` `(count ``%` `2` `=``=` `1``): ` `            ``res |``=` `(``1` `<< count) ` ` `  `        ``count``+``=``1` `        ``temp >>``=` `1` `         `  `    ``# return OR number ` `    ``return` `(n | res) ` ` `  `n ``=` `10` `print``(evenbitsetnumber(n)) ` ` `  `# This code is contributed ` `# by Smitha Dinesh Semwal `

## C#

 `// Simple C# program to set  ` `// all even bits of a number ` `using` `System; ` ` `  `class` `GFG  ` `{ ` `    ``// Sets even bits of n and  ` `    ``// returns modified number. ` `    ``static` `int` `evenbitsetnumber(``int` `n) { ` `     `  `        ``// Generate 101010...10 number ` `        ``//  and store in res. ` `        ``int` `count = 0, res = 0; ` `        ``for` `(``int` `temp = n; temp > 0; temp >>= 1) { ` `             `  `            ``// if bit is even then generate ` `            ``// number and or with res ` `            ``if` `(count % 2 == 1) ` `            ``res |= (1 << count); ` ` `  `        ``count++; ` `        ``} ` `         `  `        ``// return OR number ` `        ``return` `(n | res); ` `         `  `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `Main() ` `    ``{ ` `        ``int` `n = 4; ` `        ``Console.WriteLine(evenbitsetnumber(n)); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m.  `

## PHP

 ` 0; ``\$temp` `>>= 1)  ` `    ``{ ` ` `  `        ``// if bit is even then generate ` `        ``// number and or with res ` `        ``if` `(``\$count` `% 2 == 1) ` `            ``\$res` `|= (1 << ``\$count``); ` ` `  `        ``\$count``++; ` `    ``} ` ` `  `    ``// return OR number ` `    ``return` `(``\$n` `| ``\$res``); ` `} ` ` `  `    ``//Driver Code ` `    ``\$n` `= 10; ` `    ``echo` `evenbitsetnumber(``\$n``); ` ` `  `//This Code is contributed by mits  ` `?> `

Output:

```10
```

Method 2 (A O(1) solution for 32 bit numbers)

## C++

 `// Efficient CPP program to set all even ` `// bits of a number ` `#include ` `using` `namespace` `std; ` ` `  `// return msb set number ` `int` `getmsb(``int` `n) ` `{ ` ` `  `    ``// set all bits ` `    ``n |= n >> 1; ` `    ``n |= n >> 2; ` `    ``n |= n >> 4; ` `    ``n |= n >> 8; ` `    ``n |= n >> 16; ` ` `  `    ``// return msb ` `    ``// increment n by 1 ` `    ``// and shift by 1 ` `    ``return` `(n + 1) >> 1; ` `} ` ` `  `// return even seted number ` `int` `getevenbits(``int` `n) ` `{ ` ` `  `    ``// get msb here ` `    ``n = getmsb(n); ` ` `  `    ``// generate even bits like 101010.. ` `    ``n |= n >> 2; ` `    ``n |= n >> 4; ` `    ``n |= n >> 8; ` `    ``n |= n >> 16; ` ` `  `    ``// if bits is odd then shift by 1 ` `    ``if` `(n & 1) ` `        ``n = n >> 1; ` ` `  `    ``// return even set bits number ` `    ``return` `n; ` `} ` ` `  `// set all even bits here ` `int` `setallevenbits(``int` `n) ` `{ ` `    ``// take or with even set bits number ` `    ``return` `n | getevenbits(n); ` `} ` ` `  `int` `main() ` `{ ` `    ``int` `n = 10; ` `    ``cout << setallevenbits(n); ` `    ``return` `0; ` `} `

## Java

 `// Efficient Java program to  ` `// set all even bits of a number ` `import` `java.io.*; ` ` `  `class` `GFG  ` `{ ` `     `  `// return msb set number ` `static` `int` `getmsb(``int` `n) ` `{ ` ` `  `    ``// set all bits ` `    ``n |= n >> ``1``; ` `    ``n |= n >> ``2``; ` `    ``n |= n >> ``4``; ` `    ``n |= n >> ``8``; ` `    ``n |= n >> ``16``; ` ` `  `    ``// return msb ` `    ``// increment n by 1 ` `    ``// and shift by 1 ` `    ``return` `(n + ``1``) >> ``1``; ` `} ` ` `  `// return even seted number ` `static` `int` `getevenbits(``int` `n) ` `{ ` ` `  `    ``// get msb here ` `    ``n = getmsb(n); ` ` `  `    ``// generate even  ` `    ``// bits like 101010.. ` `    ``n |= n >> ``2``; ` `    ``n |= n >> ``4``; ` `    ``n |= n >> ``8``; ` `    ``n |= n >> ``16``; ` ` `  `    ``// if bits is odd  ` `    ``// then shift by 1 ` `    ``if` `((n & ``1``) == ``1``) ` `        ``n = n >> ``1``; ` ` `  `    ``// return even  ` `    ``// set bits number ` `    ``return` `n; ` `} ` ` `  `// set all even bits here ` `static` `int` `setallevenbits(``int` `n) ` `{ ` `    ``// take or with even ` `    ``// set bits number ` `    ``return` `n | getevenbits(n); ` `} ` ` `  `// Driver Code ` `public` `static` `void` `main (String[] args) ` `{ ` `    ``int` `n = ``10``; ` `    ``System.out.println(setallevenbits(n)); ` `} ` `} ` ` `  `// This code is contributed by ajit `

## Python3

 `# Efficient Python 3 ` `# program to set all even ` `# bits of a number ` ` `  `# return msb set number ` `def` `getmsb(n): ` ` `  `    ``# set all bits ` `    ``n |``=` `n >> ``1` `    ``n |``=` `n >> ``2` `    ``n |``=` `n >> ``4` `    ``n |``=` `n >> ``8` `    ``n |``=` `n >> ``16` ` `  `    ``# return msb ` `    ``# increment n by 1 ` `    ``# and shift by 1 ` `    ``return` `(n ``+` `1``) >> ``1` ` `  ` `  `# return even seted number ` `def` `getevenbits(n): ` `   `  `    ``# get msb here ` `    ``n ``=` `getmsb(n) ` ` `  `    ``# generate even bits like 101010.. ` `    ``n |``=` `n >> ``2`  `    ``n |``=` `n >> ``4`  `    ``n |``=` `n >> ``8`  `    ``n |``=` `n >> ``16`  ` `  `    ``# if bits is odd then shift by 1 ` `    ``if` `(n & ``1``): ` `        ``n ``=` `n >> ``1`  ` `  `    ``# return even set bits number ` `    ``return` `n  ` `  `  ` `  `# set all even bits here ` `def` `setallevenbits(n): ` `     `  `    ``# take or with even set bits number ` `    ``return` `n | getevenbits(n)  ` `  `  `n ``=` `10`  `print``(setallevenbits(n))  ` ` `  `# This code is contributed by ` `# Smitha Dinesh Semwal `

## C#

 `// Efficient C# program to  ` `// set all even bits of a number ` `using` `System; ` ` `  `class` `GFG ` `{ ` `     `  `// return msb set number ` `static` `int` `getmsb(``int` `n) ` `{ ` ` `  `    ``// set all bits ` `    ``n |= n >> 1; ` `    ``n |= n >> 2; ` `    ``n |= n >> 4; ` `    ``n |= n >> 8; ` `    ``n |= n >> 16; ` ` `  `    ``// return msb ` `    ``// increment n by 1 ` `    ``// and shift by 1 ` `    ``return` `(n + 1) >> 1; ` `} ` ` `  `// return even seted number ` `static` `int` `getevenbits(``int` `n) ` `{ ` ` `  `    ``// get msb here ` `    ``n = getmsb(n); ` ` `  `    ``// generate even  ` `    ``// bits like 101010.. ` `    ``n |= n >> 2; ` `    ``n |= n >> 4; ` `    ``n |= n >> 8; ` `    ``n |= n >> 16; ` ` `  `    ``// if bits is odd  ` `    ``// then shift by 1 ` `    ``if` `((n & 1) == 1) ` `        ``n = n >> 1; ` ` `  `    ``// return even  ` `    ``// set bits number ` `    ``return` `n; ` `} ` ` `  `// set all even bits here ` `static` `int` `setallevenbits(``int` `n) ` `{ ` `    ``// take or with even ` `    ``// set bits number ` `    ``return` `n | getevenbits(n); ` `} ` ` `  `// Driver Code ` `public` `static` `void` `Main () ` `{ ` `    ``int` `n = 10; ` ` `  `    ``Console.WriteLine(setallevenbits(n)); ` `} ` `} ` ` `  `// This code is contributed by aj_36 `

## PHP

 `> 1; ` `    ``\$n` `|= ``\$n` `>> 2; ` `    ``\$n` `|= ``\$n` `>> 4; ` `    ``\$n` `|= ``\$n` `>> 8; ` `    ``\$n` `|= ``\$n` `>> 16; ` ` `  `    ``// return msb ` `    ``// increment n by 1 ` `    ``// and shift by 1 ` `    ``return` `(``\$n` `+ 1) >> 1; ` `} ` ` `  `// return even seted number ` `function` `getevenbits(``\$n``) ` `{ ` ` `  `    ``// get msb here ` `    ``\$n` `= getmsb(``\$n``); ` ` `  `    ``// generate even bits ` `    ``// like 101010.. ` `    ``\$n` `|= ``\$n` `>> 2; ` `    ``\$n` `|= ``\$n` `>> 4; ` `    ``\$n` `|= ``\$n` `>> 8; ` `    ``\$n` `|= ``\$n` `>> 16; ` ` `  `    ``// if bits is odd then ` `    ``// shift by 1 ` `    ``if` `(``\$n` `& 1) ` `        ``\$n` `= ``\$n` `>> 1; ` ` `  `    ``// return even set ` `    ``// bits number ` `    ``return` `\$n``; ` `} ` ` `  `// set all even bits here ` `function` `setallevenbits(``\$n``) ` `{ ` `    ``// take or with even ` `    ``// set bits number ` `    ``return` `\$n` `| getevenbits(``\$n``); ` `} ` ` `  `    ``//Driver code ` `    ``\$n` `= 10; ` `    ``echo` `setallevenbits(``\$n``); ` ` `  `//This code is contributed by mits  ` `?> `

Output:

```10
```

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