# std::lcm in C++17

Competitive programming often involves computation of Least Common Multiple (LCM) of two numbers. One way of doing that is using **boost::math::lcm()**, which we discussed in the post – Inbuilt function for calculating LCM in C++ .

But, recently, C++ in its latest version C++17 has also included another in-built function for computation of LCM, **std::lcm()**. This function is defined inside the header file .

**Syntax:**

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std::lcm (m, n)Arguments:m, nReturns:0, if either of m or n are 0 else, returns lcm of mod(m) and mod(n)

Remember, since this feature has been defined in latest version of C++, so using this function in compilers not supporting C++17, will throw an error.

`// CPP program to illustrate` `// std::lcm function of C++` `#include <iostream>` `#include <numeric>` ` ` `using` `namespace` `std;` ` ` `int` `main()` `{` ` ` `cout << ` `"LCM(10, 20) = "` `<< std::lcm(10, 20)` ` ` `<< endl;` ` ` `return` `0;` `}` |

Output:

20

**Important Points:**

- This function works on
**positive numbers**, and if any argument is negative, it is firstly converted to its modulus, and then calculates the LCM. - Also, it works only on
**integer data type**, and if any other data type like char, double, is provided in its argument, then it will throw an error.

**Reference:**

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