{================================================}

{     This program is taken from the book,       }

{ "PASCAL programs in science and engineering"   }

{    by Jules H. Gilder & J. Scott Barrus        }

{   Published by, HAYDEN ISBN 0-8104-6265-6      }

{================================================}

{ Title:  Circle Finder                          }

{ Program Summary: Program will find the center  }

{ and radius of a circle that is formed by three }

{ points not in a straight line.                 }

{================================================}

 

Program Circle_Finder;

 uses Crt;

var

   cont     : Char;

    X1,X2,X3,     Y1,Y2,Y3,      Part1,    Part2,    Part3,    Part4,    X,Y,    Radius   : Real;

 

Procedure Title;

   begin

        Clrscr;

        Writeln('Circle Finder');        Writeln;

        Writeln('This program will find the center and');

        Writeln('radius of a circle that is determined');

        Writeln('by any three points in a plane that ');

        Writeln('does not form a straight line.');

        Writeln;

        Writeln('Note: For all entries that require');

        Writeln('      data entries (x,y); separate ');

        Writeln('      all data with a space.');

        Writeln;

   end;  { Title }

 

Procedure Input;

  begin

     Write('Enter first point  (X,Y):   ');

     Readln(X1,Y1);

     Write('Enter second point (X,Y):   ');

     Readln(X2,Y2);

     Write('Enter third point  (X,Y):   ');

     Readln(X3,Y3);

     Writeln;Writeln;Writeln;

  end;

 

Procedure Find;

   begin

     Part1 := ((X2-X1) * (X2+X1) + (Y2-Y1) * (Y2 + Y1)) / (2.0 * (X2-X1));

     Part2 := ((X3-X1) * (X3+X1) + (Y3-Y1) * (Y3 + Y1)) / (2.0 * (X3-X1));

     Part3 := (Y2 - Y1) / (X2 - X1);

     Part4 := (Y3 - Y1) / (X3 - X1);

{*}   If (Part3=Part4)

{*}    then begin

{*}           writeln('three points in a straight line!!! Plz, enter another three points!!!');

{*}           exit;

{*}           end;

     Y := (Part2 - Part1) / (Part4 - Part3);

     X := Part2 - Part4 * Y;

     Radius := SQRT (SQR (X3 - X) + SQR (Y3 - Y));

   end;

 

Procedure Print1;

   begin

      Writeln('The circle defined by the following');

      Writeln('three points:');

      Writeln;

      Writeln(' X1 = ',X1:7:4,' Y1 = ',Y1:7:4);

      Writeln(' X2 = ',X2:7:4,' Y2 = ',Y2:7:4);

      Writeln(' X3 = ',X3:7:4,' Y3 = ',Y3:7:4);

      Writeln;

      Writeln('has a radius = ',Radius:4:4);

      Writeln; Radius:=0;

      Writeln('at a center located at:');

      Writeln;

      Writeln(' X = ',X:4:4,'    Y = ',Y:4:4); x:=0; y:=0;

   end; { Print1 }

 

begin  { Main }

  Repeat

        Title;

        Input;

        Find;

        Print1;

          Writeln;Writeln;

          Write('Do you have another 3 points? (Y/N)');

          Readln(cont);

   Until cont in ['n','N'];

end.