# Efficient way to multiply with 7

We can multiply a number by 7 using bitwise operator. First left shift the number by 3 bits (you will get 8n) then subtract the original numberfrom the shifted number and return the difference (8n – n). **Program:**

## CPP

`# include<bits/stdc++.h> ` `using` `namespace` `std;` ` ` `//c++ implementation ` `long` `multiplyBySeven(` `long` `n) ` `{ ` ` ` `/* Note the inner bracket here. This is needed ` ` ` `because precedence of '-' operator is higher ` ` ` `than '<<' */` ` ` `return` `((n<<3) - n); ` `} ` ` ` `/* Driver program to test above function */` `int` `main() ` `{ ` ` ` `long` `n = 4; ` ` ` ` ` `cout<<multiplyBySeven(n); ` ` ` ` ` `return` `0; ` `}` |

## C

`# include<stdio.h>` `int` `multiplyBySeven(unsigned ` `int` `n)` `{ ` ` ` `/* Note the inner bracket here. This is needed ` ` ` `because precedence of '-' operator is higher ` ` ` `than '<<' */` ` ` `return` `((n<<3) - n);` `}` `/* Driver program to test above function */` `int` `main()` `{` ` ` `unsigned ` `int` `n = 4;` ` ` `printf` `(` `"%u"` `, multiplyBySeven(n));` ` ` `getchar` `();` ` ` `return` `0;` `}` |

## Java

`// Java program to multiply any ` `// positive number to 7 ` `class` `GFG {` ` ` ` ` `static` `int` `multiplyBySeven(` `int` `n)` ` ` `{ ` ` ` `/* Note the inner bracket here. ` ` ` `This is needed because precedence` ` ` `of '-' operator is higher ` ` ` `than '<<' */` ` ` `return` `((n << ` `3` `) - n);` ` ` `}` ` ` ` ` `// Driver code` ` ` `public` `static` `void` `main (String arg[]) ` ` ` `{` ` ` `int` `n = ` `4` `;` ` ` ` ` `System.out.println(multiplyBySeven(n));` ` ` `}` `}` `// This code is contributed by Anant Agarwal.` |

## Python3

`# Python program to multiply any ` `# positive number to 7 ` `# Function to multiply any number with 7 ` `def` `multiplyBySeven(n):` ` ` `# Note the inner bracket here. ` ` ` `# This is needed because ` ` ` `# precedence of '-' operator is ` ` ` `# higher than '<<' ` ` ` `return` `((n << ` `3` `) ` `-` `n)` `# Driver code ` `n ` `=` `4` `print` `(multiplyBySeven(n))` `# This code is contributed by Danish Raza` |

## C#

`// C# program to multiply any ` `// positive number to 7 ` `using` `System;` `class` `GFG` `{` ` ` `static` `int` `multiplyBySeven(` `int` `n)` ` ` `{ ` ` ` `/* Note the inner bracket here. This is needed ` ` ` `because precedence of '-' operator is higher ` ` ` `than '<<' */` ` ` `return` `((n << 3) - n);` ` ` `}` ` ` ` ` `// Driver code` ` ` `public` `static` `void` `Main () ` ` ` `{` ` ` `int` `n = 4;` ` ` `Console.Write(multiplyBySeven(n));` ` ` `}` `}` `// This code is contributed by Sam007` |

## PHP

`<?php` `function` `multiplyBySeven(` `$n` `)` `{ ` ` ` `// Note the inner bracket here.` ` ` `// This is needed because ` ` ` `// precedence of '-' operator ` ` ` `// is higherthan '<<' ` ` ` `return` `((` `$n` `<<3) - ` `$n` `);` `}` ` ` `// Driver Code` ` ` `$n` `= 4;` ` ` `echo` `multiplyBySeven(` `$n` `);` `// This code is contributed by vt_m.` `?>` |

## Javascript

`<script>` ` ` `function` `multiplyBySeven(n)` `{ ` ` ` `/* Note the inner bracket here. This is needed ` ` ` `because precedence of '-' operator is higher ` ` ` `than '<<' */` ` ` `return` `((n << 3) - n);` `}` ` ` `// Driver program to test above function ` ` ` `n = 4;` ` ` `document.write(multiplyBySeven(n));` ` ` ` ` `// This code is contributed by simranarora5sos` `</script>` |

**Output:**

28

**Time Complexity: **O(1) **Space Complexity:** O(1)

Note: Works only for positive integers.

Same concept can be used for fast multiplication by 9 or other numbers.