Cú pháp khai báo biến khai báo bằng: Const [Tên hằng]=[Giá trị hằng];

Program ct;
uses crt;
var S,a,b:real;
begin
    clrscr;
    writeln('--HINH TAM GIAC--');
    writeln('Nhap a,h:'); readln(a,b);
    writeln('Dien tich hinh tam giac la: ',(a*b)/2:5:2);
    writeln;
    writeln('--HINH VUONG--');
    writeln('Nhap a:'); readln(a);
    writeln('Dien tich hinh vuong la: ',a*a:5:2);
    writeln;
    writeln('--HINH CHU NHAT--');
    writeln('Nhap a,b:'); readln(a,b);
    writeln('Dien tich hinh chu nhat la: ',a*b:5:2);
    writeln;
    writeln('--HINH BINH HANH--');
    writeln('Nhap a,h:'); readln(a,b);
    writeln('Dien tich hinh binh hanh la: ',a*b:5:2);
    writeln;
    writeln('--HINH THOI--');
    writeln('Nhap m,n:'); readln(a,b);
    writeln('Dien tich hinh thoi la: ',(a*b)/2:5:2);
    readln;
end.