*Viết chương trình tính diện tích hình vuông
program dientich; 
uses crt; 
var S,a:integer; 
begin 
writeln('nhap a'); 
readln(a); 
S:=a*a; 
writeln('ketqua',S); 
readln; 
end.

* program Hinh_chu_nhat;

uses crt;

var a,b,S,: integer;

begin

writeln('Nhap chieu dai:');

readln(a);

writeln('Nhap chieu rong:');

readln(b);

S:=(a*b);

writeln('Dien tich la:',S);

readln

end.

* Program S_Hinh_Tron;
Uses Crt;
Var r,S:real;
Begin
Clrscr;
Writeln(‘TINH DIEN TICH HINH TRON:’);
Write (‘Nhap ban kinh R=’);readln(r);
dt:=pi*r*r;
Writeln(‘Dien tich hinh tron la:’,dt:6:2);
Readln;
End.

*

Program dien_tich_hinh_thang;

uses crt;

var a,b,h: real;

begin

clrscr;

write('nhap a = '); readln(a);

write('nhap b = '); readln(b);

write('nhap h = '); readln(h);

writeln('dien tich hinh thang =' ,(1/2)*h*(a+b):4:2);

readln;

end.

Program BTT;
Uses crt;
Const pi=3.14;
Var a,b,h,s,r: extended;
    k: 1..4;
Begin
        Clrscr;
        Writeln('1. Hinh vuong: ');
        Writeln('2. Hinh chu nhat: ');
        Writeln('3. Hinh tron: ');
        Writeln('4. Hinh thang: ');
        Write('Chon hinh can tinh dien tich (1 -> 4): '); Readln(k);

        If k=1 then
        Begin
                Write('Nhap do dai canh: '); Readln(a);
                s:=sqr(a);
        End;

        If k=2 then
        Begin
                Write('Nhap chieu dai va chieu rong: '); Readln(a,b);
                s:=a*b;
        End;

        If k=3 then
        Begin
                Write('Nhap ban kinh: '); Readln(r);
                s:=sqr(r)*pi;
        End;

        If k=4 then
        Begin
                Write('Nhap do dai 2 day: '); Readln(a,b);
                Write('Nhap chieu cao: '); Readln(h);
                s:=(a+b)*h/2;
        End;

        Write('Dien tich cua hinh do la: ',s:0:2);
        Readln
End.