function Arg (z: Complex): Real;
Arg returns the complex “argument”, i.e. the angle (in radian) in the complex plane with respect to the real axis, of its parameter z. The result is in the range of -Pi < Arg (z) <= Pi.
Arg is an ISO 10206 Extended Pascal extension.
program ArgDemo; var z: Complex; begin z := Cmplx (1, 1); { 1 + i } WriteLn (Arg (z) : 0 : 5) { yields 0.78540, i.e. Pi / 4 } end.