# Set all odd bits of a number

Given a number, the task is to set all odd bits 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 : 21
Explanation : Binary representation of 20
is 10100. Setting all odd
bits make the number 10101 which is binary
representation of 21.

Input : 10
Output : 15
```

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

Method 1 (Using XOR)

1. First generate a number that contains odd 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++

 `// CPP code Set all odd bits  ` `// of a number ` `#include ` `using` `namespace` `std; ` ` `  `// set all odd bit ` `int` `oddbitsetnumber(``int` `n) ` `{ ` `    ``int` `count = 0; ` ` `  `    ``// res for store 010101.. number ` `    ``int` `res = 0; ` ` `  `    ``// generate number form of 010101.....till ` `    ``// temp size ` `    ``for` `(``int` `temp = n; temp > 0; temp >>= 1) { ` ` `  `        ``// if bit is odd, then generate ` `        ``// number and or with res ` `        ``if` `(count % 2 == 0) ` `            ``res |= (1 << count); ` ` `  `        ``count++; ` `    ``} ` ` `  `    ``return` `(n | res); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 10; ` `    ``cout << oddbitsetnumber(n); ` `    ``return` `0; ` `} `

## Java

 `// Java code to Set all odd  ` `// bits of a number ` ` `  `class` `GFG  ` `{ ` ` `  `    ``// set all odd bit ` `    ``static` `int` `oddbitsetnumber(``int` `n) ` `    ``{ ` `        ``int` `count = ``0``; ` ` `  `        ``// res for store 010101.. number ` `        ``int` `res = ``0``; ` ` `  `        ``// generate number form of  ` `        ``// 010101.....till temp size ` `        ``for` `(``int` `temp = n; temp > ``0``; temp >>= ``1``)  ` `        ``{ ` ` `  `            ``// if bit is odd, then generate ` `            ``// number and or with res ` `            ``if` `(count % ``2` `== ``0``) ` `                ``res |= (``1` `<< count); ` ` `  `            ``count++; ` `        ``} ` ` `  `        ``return` `(n | res); ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``int` `n = ``10``; ` `        ``System.out.println(oddbitsetnumber(n)); ` `    ``} ` `} ` ` `  `// This code is contributed  ` `// by prerna saini `

## Python3

 `''' Python3 code Set all odd bits  ` `   ``of a number'''` `    `  `# set all odd bit ` `def` `oddbitsetnumber(n): ` `    ``count ``=` `0` `    ``# res for store 010101.. number ` `    ``res ``=` `0` ` `  `    ``# generate number form of 010101.....till ` `    ``# temp size ` `    ``temp ``=` `n ` `    ``while` `temp > ``0``: ` ` `  `        ``# if bit is odd, then generate ` `        ``# number and or with res ` `        ``if` `count ``%` `2` `=``=` `0``: ` `            ``res |``=` `(``1` `<< count) ` ` `  `        ``count ``+``=` `1` `        ``temp >>``=` `1` ` `  `    ``return` `(n | res) ` ` `  `n ``=` `10` `print` `(oddbitsetnumber(n)) ` ` `  `#This code is contributed by Shreyanshi Arun. `

## C#

 `// C# code to Set all odd  ` `// bits of a number ` `using` `System; ` ` `  `class` `GFG ` `{ ` `    ``static` `int` `oddbitsetnumber(``int` `n) ` `    ``{ ` `        ``int` `count = 0; ` ` `  `        ``// res for store 010101.. number ` `        ``int` `res = 0; ` ` `  `        ``// generate number form of  ` `        ``// 010101.....till temp size ` `        ``for` `(``int` `temp = n; temp > 0;  ` `                           ``temp >>= 1)  ` `        ``{ ` ` `  `            ``// if bit is odd, then  ` `            ``// generate number and  ` `            ``// or with res ` `            ``if` `(count % 2 == 0) ` `                ``res |= (1 << count); ` ` `  `            ``count++; ` `        ``} ` ` `  `        ``return` `(n | res); ` `    ``} ` `     `  `    ``// Driver Code ` `    ``static` `public` `void` `Main () ` `    ``{ ` `        ``int` `n = 10; ` `        ``Console.WriteLine(oddbitsetnumber(n)); ` `    ``} ` `} ` ` `  `// This code is contributed  ` `// by prerna ajit `

## PHP

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

Output:

```15
```

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

## C++

 `// Efficient CPP program to set all  ` `// odd bits number ` `#include ` `using` `namespace` `std; ` ` `  `// return MSB set number ` `int` `getmsb(``int` `n) ` `{ ` `    ``// set all bits including MSB. ` `    ``n |= n >> 1; ` `    ``n |= n >> 2; ` `    ``n |= n >> 4; ` `    ``n |= n >> 8; ` `    ``n |= n >> 16; ` ` `  `    ``// return MSB ` `    ``return` `(n + 1) >> 1; ` `} ` ` `  `// Returns a number of same size (MSB at ` `// same position) as n and all odd bits ` `// set. ` `int` `getevenbits(``int` `n) ` `{ ` `    ``n = getmsb(n); ` ` `  `    ``// generate odd bits like 010101.. ` `    ``n |= n >> 2; ` `    ``n |= n >> 4; ` `    ``n |= n >> 8; ` `    ``n |= n >> 16; ` ` `  `    ``// if bits is even then shift by 1 ` `    ``if` `((n&1) == 0) ` `        ``n = n >> 1; ` `     `  `    ``// return odd set bits number ` `    ``return` `n;   ` `} ` ` `  `// set all odd bits here ` `int` `setalloddbits(``int` `n) ` `{     ` `    ``// take OR with odd set bits number ` `    ``return` `n | getevenbits(n);     ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 10; ` `    ``cout << setalloddbits(n); ` `    ``return` `0;  ` `} `

## Java

 `// Efficient Java program to set ` `// all odd bits number ` `class` `GFG { ` ` `  `    ``// return MSB set number ` `    ``static` `int` `getmsb(``int` `n) ` `    ``{ ` `        ``// set all bits including MSB. ` `        ``n |= n >> ``1``; ` `        ``n |= n >> ``2``; ` `        ``n |= n >> ``4``; ` `        ``n |= n >> ``8``; ` `        ``n |= n >> ``16``; ` ` `  `        ``// return MSB ` `        ``return` `(n + ``1``) >> ``1``; ` `    ``} ` ` `  `    ``// Returns a number of same  ` `    ``// size (MSB at same position)  ` `    ``// as n and all odd bits set. ` `    ``static` `int` `getevenbits(``int` `n) ` `    ``{ ` `        ``n = getmsb(n); ` ` `  `        ``// generate odd bits  ` `        ``// like 010101.. ` `        ``n |= n >> ``2``; ` `        ``n |= n >> ``4``; ` `        ``n |= n >> ``8``; ` `        ``n |= n >> ``16``; ` ` `  `        ``// if bits is even  ` `        ``// then shift by 1 ` `        ``if` `((n & ``1``) == ``0``) ` `            ``n = n >> ``1``; ` ` `  `        ``// return odd set bits number ` `        ``return` `n; ` `    ``} ` ` `  `    ``// set all odd bits here ` `    ``static` `int` `setalloddbits(``int` `n) ` `    ``{ ` `        ``// take OR with odd  ` `        ``// set bits number ` `        ``return` `n | getevenbits(n); ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``int` `n = ``10``; ` `        ``System.out.println(setalloddbits(n)); ` `    ``} ` `} ` ` `  `// This code is contributed  ` `// by prerna saini `

## Python3

 `# Efficient python3 program to   ` `# set all odd bits number ` `import` `math ` ` `  `# return MSB set number ` `def` `getmsb( n): ` ` `  `    ``# set all bits including MSB. ` `    ``n |``=` `n >> ``1` `    ``n |``=` `n >> ``2` `    ``n |``=` `n >> ``4` `    ``n |``=` `n >> ``8` `    ``n |``=` `n >> ``16` ` `  `    ``# return MSB ` `    ``return` `(n ``+` `1``) >> ``1` ` `  ` `  `# Returns a number of same ` `# size (MSB at same position)  ` `# as n and all odd bits set. ` `def` `getevenbits(n): ` ` `  `    ``n ``=` `getmsb(n) ` ` `  `    ``# generate odd bits  ` `    ``# like 010101.. ` `    ``n |``=` `n >> ``2` `    ``n |``=` `n >> ``4` `    ``n |``=` `n >> ``8` `    ``n |``=` `n >> ``16` ` `  `    ``# if bits is even  ` `    ``# then shift by 1 ` `    ``if` `((n & ``1``) ``=``=` `0``): ` `        ``n ``=` `n >> ``1` `     `  `    ``# return odd set bits number ` `    ``return` `n ` ` `  ` `  `# set all odd bits here ` `def` `setalloddbits( n): ` ` `  `    ``# take OR with odd  ` `    ``# set bits number ` `    ``return` `n | getevenbits(n) ` ` `  ` `  `# Driver Program  ` `n ``=` `10` `print``(setalloddbits(n)) ` `     `  ` `  `# This code is contributed  ` `# by Gitanjali. `

## C#

 `// Efficient C# program to  ` `// set all odd bits number ` `using` `System; ` ` `  `class` `GFG ` `{ ` `     `  `    ``// return MSB set number ` `    ``static` `int` `getmsb(``int` `n) ` `    ``{ ` `        ``// set all bits ` `        ``// including MSB. ` `        ``n |= n >> 1; ` `        ``n |= n >> 2; ` `        ``n |= n >> 4; ` `        ``n |= n >> 8; ` `        ``n |= n >> 16; ` ` `  `        ``// return MSB ` `        ``return` `(n + 1) >> 1; ` `    ``} ` `     `  `    ``// Returns a number of same  ` `    ``// size (MSB at same position)  ` `    ``// as n and all odd bits set. ` `    ``static` `int` `getevenbits(``int` `n) ` `    ``{ ` `        ``n = getmsb(n); ` ` `  `        ``// generate odd bits  ` `        ``// like 010101.. ` `        ``n |= n >> 2; ` `        ``n |= n >> 4; ` `        ``n |= n >> 8; ` `        ``n |= n >> 16; ` ` `  `        ``// if bits is even  ` `        ``// then shift by 1 ` `        ``if` `((n & 1) == 0) ` `            ``n = n >> 1; ` ` `  `        ``// return odd  ` `        ``// set bits number ` `        ``return` `n; ` `    ``} ` ` `  `    ``// set all odd bits here ` `    ``static` `int` `setalloddbits(``int` `n) ` `    ``{ ` `        ``// take OR with odd  ` `        ``// set bits number ` `        ``return` `n | getevenbits(n); ` `    ``} ` ` `  `    ``// Driver Code ` `    ``static` `public` `void` `Main () ` `    ``{ ` `        ``int` `n = 10; ` `        ``Console.WriteLine(setalloddbits(n)); ` `    ``} ` `} ` ` `  `// This code is contributed ajit `

## PHP

 `> 1; ` `    ``\$n` `|= ``\$n` `>> 2; ` `    ``\$n` `|= ``\$n` `>> 4; ` `    ``\$n` `|= ``\$n` `>> 8; ` `    ``\$n` `|= ``\$n` `>> 16; ` ` `  `    ``// return MSB ` `    ``return` `(``\$n` `+ 1) >> 1; ` `} ` ` `  `// Returns a number of ` `// same size (MSB at ` `// same position) as n  ` `// and all odd bits set ` `function` `getevenbits(``\$n``) ` `{ ` `    ``\$n` `= getmsb(``\$n``); ` ` `  `    ``// generate odd bits  ` `    ``// like 010101.. ` `    ``\$n` `|= ``\$n` `>> 2; ` `    ``\$n` `|= ``\$n` `>> 4; ` `    ``\$n` `|= ``\$n` `>> 8; ` `    ``\$n` `|= ``\$n` `>> 16; ` ` `  `    ``// if bits is even  ` `    ``// then shift by 1 ` `    ``if` `((``\$n``&1) == 0) ` `        ``\$n` `= ``\$n` `>> 1; ` `     `  `    ``// return odd set ` `    ``// bits number ` `    ``return` `\$n``;  ` `} ` ` `  `// set all odd bits here ` `function` `setalloddbits(``\$n``) ` `{  ` `     `  `    ``// take OR with odd  ` `    ``// set bits number ` `    ``return` `\$n` `| getevenbits(``\$n``);  ` `} ` ` `  `    ``// Driver code ` `    ``\$n` `= 10; ` `    ``echo` `setalloddbits(``\$n``); ` ` `  `// This code is contributed by mits  ` `?> `

Output:

```15
```

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