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

**Syntax:**

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

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

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

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

Output:

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

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