VMS Help CC, Run-time functions, cabs  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Computes the Euclidean distance between two points as the square
  root of their respective squares.  This function returns
  sqrt(x*x + y*y).

  Syntax:

       #include <math.h>

       double cabs(cabs_t z);