(* This program calculates the area of the circle or the volume and surface area of the sphere. New concepts introduced are functions, procedures, and variables*)


PROGRAM practice (input, output);
CONST
   PI =  3.141592654;

(*Function calculates circle area*)
FUNCTION circleArea (radius : real):real;
BEGIN
   circleArea := PI * radius * radius;
END; { circleArea }


(*Calculate sphere volume*)
FUNCTION sphereVolume (radius :  real) : real;
BEGIN
   sphereVolume := 4.0/3.0 * PI * radius * radius * radius;
END;

(* calculate surfacearea *)
FUNCTION sphereSurfaceArea (radius :  real):real;
BEGIN
   sphereSurfaceArea := 4 * PI * radius * radius;
END; { sphereSurfaceArea }


(*calls sphereSurfaceArea and sphereVolume*)
PROCEDURE sphereCalc (    radius : real; 
                      var volume : real;
                      var area   : real);
BEGIN
   volume := sphereVolume (radius);
   area := sphereSurfaceArea (radius);
END; { sphereCalc }


BEGIN
   var radius : real;
   var sVolume: real;
   var sArea  : real;
   var choice : char;

   repeat
      writeln ('Welcome to circle and sphere calculator');
      writeln ('(c)ircle''s surface area');
      writeln ('(s)phere''s surface area and volumne.');
      writeln ('(q)uit the program');
      write ('Enter choice now');
      readln (choice);
      
      case (choice) of
	'C', 'c' : 
	   Begin
	      write ('Enter the radius of the circle');
	      readln (radius);
	      writeln ('The area of the circle with radius ', radius:4:2,' is ', circleArea(radius):4:2);
	   end;

	 'S', 's': 
	   Begin
	      write ('Enter the radius of the sphere');
	      readln (radius);
	      sphereCalc (radius, sVolume, sArea);
	      writeln ('The surface area of the circle with radius ', radius:4:2,' is ', sArea:4:2,
                       'and the volume is ',sVolume:4:2 );
	   end;

          'Q', 'q':
	      writeln('Quiting program.');
      End;
   until (choice = 'Q') or (choice ='q');
END.