Program TINH_DIEN_TICH;
Uses crt;
Procedure HV;
  Var s,a:real;
  Begin
      Writeln('TINH DIEN TICH HINH VUONG:');
      Write('Nhap chieu dai cua canh a = ');readln(a);
      s:=a*a;
     Writeln('Dien tich hinh vuong = ',s:6:2);
  End;
Procedure HT;
Var s,r:real;
Begin
     Writeln('TINH DIEN TICH HINH TRON:');
     Write('Nhap ban kinh R = ');readln(r);
     s:=pi*r*r;
     Writeln('Dien tich hinh tron = ',s:6:2);
End;
Procedure TG;
Var a, b, c,s,p:real;
 Begin
    Writeln('TINH DIEN TICH TAM GIAC:');
    Write('nhap a =');readln(a);
    Write ('nhap b =');readln(b);
    Write('nhap c =');readln(c);
    If ((a+b)>c)and((b+c)>a)and((a+c)>b) then
    Begin
         p:=(a+b+c)/2;
         s:=sqrt(p*(p-a)*(p-b)*(p-c));
         Writeln('Chu vi tam giac:',2*p:4:2) ;
         Writeln('Dien tich tam giac:',s:4:2);
     End
     Else
          Writeln(a,', ',', ',c,' khong phai la ba canh cua tam giac') ;
End;
Procedure CN;
Var a, b, s:real;
Begin
     Writeln('TINH DIEN TICH HINH CHU NHAT:');
     Write('Nhap chieu dai a =');readln(a);
     Write('Nhap chieu rong b= ');readln(b);
     s:= a*b;
     Writeln('Dien tich hinh chu nhat, s= ',s:6:2);
End;
Procedure menu;
Var d:integer;
Begin
     Clrscr;
     Writeln('CHON MOT TRONG CAC PHUONG AN SAU:');
     Writeln('----------------------------------');
     Writeln('0: Quay ve man hinh soan thao');
     Writeln('1: Tinh dien tich hinh vuong');
      Writeln('2: Tinh dien tich hinh tron');
     Writeln('3: tinh dien tich tam giac');
     Writeln('4: Tinh dien tich hinh chu nhat');
     Writeln('====================');
    Write(' Hay chon mot phuong an: '); readln(d);
    Writeln('====================');
    Writeln;
   Case d of
       0: Exit;
       1: HV;
       2: HT;
       3: TG;
       4: CN;
    End;
End;
Begin
     menu;
    Readln;
End.