Suppose a variable x can have only two possible values a and b, and you wish to assign to x the value other than its current one. Do it efficiently without using any conditional operator.

Note : We are not allowed to check current value of x.

Examples:

Input : a = 10, b = 15, x = a

Output : x = 15

Explanation x = 10, currently x has value of a (which is 10), we need to change it to 15.Input : a = 9, b = 11, x = b

Output : x = 9

We could solve this problem using if condition, but we are not allowed to do that.

if (x == a) x = b; else x = a;

We could have used Ternary operator, it also checks the current value of x and based on that it assigns new value. So we cannot use this approach as well

x = x == a ? b : a;

But, we are not allowed to check value of x, so none of the above solutions work.

**Solution 1:** Using arithmetic operators only we can perform this operation

x = a + b - x

This way the content of x will alternate between a and b every time it gets executed

## C++

`// CPP program to change value of x ` `// according to its current value. ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// Function to alternate the values ` `void` `alternate(` `int` `& a, ` `int` `& b, ` `int` `& x) ` `{ ` ` ` `x = a + b - x; ` `} ` ` ` `// Main function ` `int` `main() ` `{ ` ` ` `int` `a = -10; ` ` ` `int` `b = 15; ` ` ` `int` `x = a; ` ` ` `cout << ` `"x is : "` `<< x; ` ` ` ` ` `alternate(a, b, x); ` ` ` ` ` `cout << ` `"\nAfter change "` `; ` ` ` `cout << ` `"\nx is : "` `<< x; ` `} ` |

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## Java

`// Java program to change value of x ` `// according to its current value. ` `import` `java.util.*; ` ` ` `class` `solution ` `{ ` ` ` `// Function to alternate the values ` `static` `void` `alternate(` `int` `a, ` `int` `b, ` `int` `x) ` `{ ` ` ` `x = a + b - x; ` ` ` `System.out.println(` `"After change"` `+` `"\n"` `+` `" x is : "` `+x); ` `} ` ` ` `// Main function ` `public` `static` `void` `main(String args[]) ` `{ ` ` ` `int` `a = -` `10` `; ` ` ` `int` `b = ` `15` `; ` ` ` `int` `x = a; ` ` ` `System.out.println(` `"x is : "` `+x); ` ` ` `alternate(a, b, x); ` `} ` `} ` |

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## Python3

`# Python3 program to change value ` `# of x according to its current value. ` ` ` `# Function to alternate the values ` `def` `alternate(a,b,x): ` ` ` `x ` `=` `a` `+` `b` `-` `x ` ` ` `print` `(` `"After change x is:"` `,x) ` ` ` ` ` `# Driver code ` `if` `__name__` `=` `=` `'__main__'` `: ` ` ` `a ` `=` `-` `10` ` ` `b ` `=` `15` ` ` `x ` `=` `a ` ` ` `print` `(` `"x is:"` `,x) ` ` ` `alternate(a,b,x) ` ` ` `# This code is contributed by ` `# Shrikant13 ` |

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## C#

`// C# program to change value of x ` `// according to its current value. ` ` ` `using` `System; ` `class` `gfg ` `{ ` ` ` `// Function to alternate the values ` ` ` `public` `void` `alternate(` `ref` `int` `a, ` `ref` `int` `b, ` `ref` `int` `x) ` ` ` `//'ref' indicates the references ` ` ` `{ ` ` ` `x = a + b - x; ` ` ` `} ` `} ` ` ` `// Main function ` `class` `geek ` `{ ` ` ` `public` `static` `int` `Main() ` ` ` `{ ` ` ` `gfg g = ` `new` `gfg(); ` ` ` `int` `a = -10; ` ` ` `int` `b = 15; ` ` ` `int` `x = a; ` ` ` `Console.WriteLine(` `"x is : {0}"` `, x); ` ` ` ` ` `g.alternate(` `ref` `a, ` `ref` `b, ` `ref` `x); ` ` ` ` ` `Console.WriteLine (` `"After change "` `); ` ` ` `Console.WriteLine(` `"x is : {0}"` `, x); ` ` ` `return` `0; ` ` ` `} ` `} ` `//This code is contributed by Soumik ` |

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## PHP

`<?php ` `// PHP program to change value of x ` `// according to its current value. ` ` ` `// Function to alternate the values ` `function` `alternate (&` `$a` `, &` `$b` `, &` `$x` `) ` `{ ` ` ` `$x` `= ` `$a` `+ ` `$b` `- ` `$x` `; ` `} ` ` ` `// Driver Code ` `$a` `= -10; ` `$b` `= 15; ` `$x` `= ` `$a` `; ` `echo` `"x is : "` `, ` `$x` `; ` ` ` `alternate(` `$a` `, ` `$b` `, ` `$x` `); ` ` ` `echo` `"\nAfter change "` `; ` `echo` `"\nx is : "` `, ` `$x` `; ` ` ` `// This code is contributed by ajit. ` `?> ` |

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**Output:**

x is : -10 After change x is : 15

**Time Complexity:** The time complexity of this approach is O(1)

**Space Complexity:** The space complexity of this approach is O(1)

**Solution 2:** A better and efficient approach is using the bitwise XOR operation.

x = a^b^x

## C++

`// CPP program to change value of x ` `// according to its current value. ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// Function to alternate the values ` `void` `alternate(` `int` `& a, ` `int` `& b, ` `int` `& x) ` `{ ` ` ` `x = a ^ b ^ x; ` `} ` ` ` `// Main function ` `int` `main() ` `{ ` ` ` `int` `a = -10; ` ` ` `int` `b = 15; ` ` ` `int` `x = a; ` ` ` `cout << ` `"x is : "` `<< x; ` ` ` ` ` `alternate(a, b, x); ` ` ` ` ` `cout << ` `"\nAfter exchange "` `; ` ` ` `cout << ` `"\nx is : "` `<< x; ` ` ` ` ` `return` `0; ` `} ` |

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## Java

`// Java program to change value of x ` `// according to its current value. ` ` ` `class` `GFG { ` `// Function to alternate the values ` ` ` ` ` `static` `int` `alternate(` `int` `a, ` `int` `b, ` `int` `x) { ` ` ` `return` `x = a ^ b ^ x; ` ` ` `} ` ` ` `// Main function ` ` ` `public` `static` `void` `main(String[] args) { ` ` ` `int` `a = -` `10` `; ` ` ` `int` `b = ` `15` `; ` ` ` `int` `x = a; ` ` ` `System.out.print(` `"x is : "` `+ x); ` ` ` ` ` `x = alternate(a, b, x); ` ` ` ` ` `System.out.print(` `"\nAfter exchange "` `); ` ` ` `System.out.print(` `"\nx is : "` `+ x); ` ` ` ` ` `} ` `} ` ` ` `// This code is contributed by 29AjayKumar ` |

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## Python3

`# Python3 program to change value of x ` `# according to its current value. ` ` ` `# Function to alternate the values ` `def` `alternate(a, b, x): ` ` ` `x ` `=` `a ^ b ^ x ` ` ` `print` `(` `"After exchange"` `) ` ` ` `print` `(` `"x is"` `, x) ` ` ` `# Driver code ` `a ` `=` `-` `10` `b ` `=` `15` `x ` `=` `a ` `print` `(` `"x is"` `, x) ` `alternate(a, b, x) ` ` ` `# This code is contributed ` `# by Shrikant13 ` |

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## C#

` ` `// C# program to change value of x ` `// according to its current value. ` `using` `System; ` `public` `class` `GFG { ` `// Function to alternate the values ` ` ` ` ` `static` `int` `alternate(` `int` `a, ` `int` `b, ` `int` `x) { ` ` ` `return` `x = a ^ b ^ x; ` ` ` `} ` ` ` `// Main function ` ` ` `public` `static` `void` `Main() { ` ` ` `int` `a = -10; ` ` ` `int` `b = 15; ` ` ` `int` `x = a; ` ` ` `Console.Write(` `"x is : "` `+ x); ` ` ` ` ` `x = alternate(a, b, x); ` ` ` ` ` `Console.Write(` `"\nAfter exchange "` `); ` ` ` `Console.Write(` `"\nx is : "` `+ x); ` ` ` ` ` `} ` `} ` `/*This code is contributed by Rajput-Ji*/` |

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## PHP

`<?php ` `// PHP program to change value of x ` `// according to its current value. ` ` ` `// Function to alternate the values ` `function` `alternate(&` `$a` `, &` `$b` `, &` `$x` `) ` `{ ` ` ` `$x` `= ` `$a` `^ ` `$b` `^ ` `$x` `; ` `} ` ` ` `// Driver Code ` `$a` `= -10; ` `$b` `= 15; ` `$x` `= ` `$a` `; ` `echo` `"x is : "` `, ` `$x` `; ` ` ` `alternate(` `$a` `, ` `$b` `, ` `$x` `); ` ` ` `echo` `"\nAfter exchange "` `; ` `echo` `"\nx is : "` `, ` `$x` `; ` ` ` `// This code is contributed ` `// by akt_mit ` `?> ` |

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**Output:**

x is : -10 After exchange x is : 15

**Time Complexity:** The time complexity of this approach is O(1)

**Space Complexity:** The space complexity of this approach is O(1)

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