# std::gcd | C++ inbuilt function for finding GCD

In many competitive programming problems, we need to find greatest common divisor also known as **gcd**. Euclids algorithm to find gcd has been discussed here.

C++ has the built-in function for calculating GCD. This function is present in header file. **Syntax for C++14 :**

Library:'algorithm'__gcd(m, n)Parameter :m, nReturn Value :0 if both m and n are zero, else gcd of m and n.

**Syntax for C++17 :**

Library:'numeric'gcd(m, n)Parameter :m, nReturn Value :0 if both m and n are zero, else gcd of m and n.

## CPP

`// CPP program to illustrate` `// gcd function of C++ STL` `#include <iostream>` `#include <algorithm>` `// #include<numeric> for C++17` `using` `namespace` `std;` `int` `main()` `{` ` ` `cout << ` `"gcd(6, 20) = "` `<< __gcd(6, 20) << endl; ` `// gcd(2.0,8) for C++17` `}` |

**Output**

gcd(6, 20) = 2

**Note: **If either M or N is not an integer type, or if either is (possibly cv-qualified) bool, the program is ill-formed. Also, If either |m| or |n| is not representable as a value of type std::common_type_t, the behavior is undefined.

## CPP

`// CPP program to illustrate` `// undefined behavior of` `// gcd function of C++ STL` `#include <iostream>` `#include <algorithm>` `// #include<numeric> for C++17` `using` `namespace` `std;` `int` `main()` `{` ` ` `cout << ` `"gcd(6, 20) = "` `<< __gcd(2.0, 8) << endl; ` `// gcd(2.0,8) for C++17` `}` |

Output:

Error, As the data type float is not supported by std::gcd.

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