#include <math.h>
double hypot(double x, double y);
hypot compute the square root of the sum of the squares of x and y, sqrt(x*x + y*y), without undue overflow or underflow. If x and y are the lengths of the sides of a right-angled triangle, then hypot computes the length of the hypotenuse..
If x or y is +? or -?, hypot
returns ?.
If x or y is NaN, hypot returns
NaN.
hypot conforms to ISO/IEC 9899:1999 (C99).