Uses Graph, CRT;

Const
 Dx=0.1;
 x0=1.0;
 b=4.0;
 y0=2.0;

Var
 GraphDevice, GraphMode: integer;
 x,y,Kx,Ky,D:Real;
 i,N:Integer;
 S:String;

Function Accur(z:real):real;
begin
 Accur:=z+1;
end;

Function Der(Xd,Yd:real):real;
begin
 Der:=Yd/(Xd+1);
end;

Begin
 N:=Round((b-x0)/Dx);
 GraphDevice := Detect;
 GraphMode := Detect;
 InitGraph(GraphDevice, GraphMode, '');
 if GraphResult <> grOk then
  begin
   writeln('Error');
   Exit;
  end;
 SetLineStyle(SolidLn,0,ThickWidth);
 Line(30,GetMaxY-40,GetMaxX-10,GetMaxY-40);
 Line(30,GetMaxY-40,30,20);
 SetTextJustify(CenterText,TopText);
 OutTextXY(GetMaxX-15,GetMaxY-30,'X');
 SetTextJustify(LeftText,CenterText);
 OutTextXY(12,25,'Y');
 Kx:=(GetMaxX-40)/5;
 Ky:=(GetMaxY-60)/7;
 SetLineStyle(SolidLn,0,NormWidth);
 SetTextJustify(CenterText,TopText);
 for i:=0 to 4 do
  begin
   Line(Round(30+i*Kx),GetMaxY-34,Round(30+i*Kx),GetMaxY-40);
   Str(i,S);
   OutTextXY(Round(30+i*Kx),GetMaxY-30,S);
  end;
 SetTextJustify(RightText,CenterText);
 for i:=0 to 6 do
  begin
   Line(30,Round(GetMaxY-40-i*Ky),24,Round(GetMaxY-40-i*Ky));
   Str(i,S);
   OutTextXY(20,Round(GetMaxY-40-i*Ky),S);
  end;
 SetColor(LightRed);
 Line(30,Round(GetMaxY-40-Accur(0)*Ky),Round(30+5*Kx),Round(GetMaxY-40-Accur(5)*Ky));
 SetTextJustify(LeftText,CenterText);
 Line(50,50,70,50);
 OutTextXY(80,50,'Accurate function');
 SetColor(Yellow);
 Line(50,80,70,80);
 OutTextXY(80,80,'Euler method');
 SetFillStyle(SolidFill,Yellow);
 FillEllipse(60,80,2,2);
 x:=x0;
 y:=y0;
 SetFillStyle(SolidFill,Yellow);
 FillEllipse(Round(30+x*Kx),Round(GetMaxY-40-y*Ky),2,2);
 MoveTo(Round(30+x*Kx),Round(GetMaxY-40-y*Ky));
 for i:=1 to N do
  begin
   D:=Der(x,y);
   x:=x+Dx;
   y:=y+D*Dx;
   FillEllipse(Round(30+x*Kx),Round(GetMaxY-40-y*Ky),2,2);
   LineTo(Round(30+x*Kx),Round(GetMaxY-40-y*Ky));
  end;
 ReadKey
End.