uses crt;
var choose:byte;

procedure Thoat;
var i:byte;
begin
    writeln('  Ban chon thoat!');
    write(' * Chuong trinh thoat sau 3s');
    for i:=1 to 3 do 
    begin
        write('.');
        delay(1000);
    end;
    halt;
end;

procedure cong;
var a,b,kq:real;
begin
    writeln('----------------');
    writeln(' Ban chon phep cong!');
    writeln;
    write('- Nhap so a: ')    ; readln(a);
    write('- Nhap so b: ')    ; readln(b);
    kq := a+b;
    write(a:0:3,' + ',b:0:3,' = ',kq:0:3);
end;

procedure tru;
var a,b,kq:real;
begin
    writeln('----------------');
    writeln(' Ban chon phep tru!');
    writeln;
    write('- Nhap so a: ')    ; readln(a);
    write('- Nhap so b: ')    ; readln(b);
    kq := a-b;
    write(a:0:3,' - ',b:0:3,' = ',kq:0:3);
end;

procedure nhan;
var a,b,kq:real;
begin
    writeln('----------------');
    writeln(' Ban chon phep nhan!');
    writeln;
    write('- Nhap so a: ')    ; readln(a);
    write('- Nhap so b: ')    ; readln(b);
    kq := a*b;
    write(a:0:3,' x ',b:0:3,' = ',kq:0:3);
end;

procedure chia;
var a,b,kq:real;
begin
    writeln('----------------');
    writeln(' - Ban chon phep chia!');
    writeln;
    write('- Nhap so a: ')    ; readln(a);
    write('- Nhap so b: ')    ; readln(b);
    if b=0 then writeln(' Khong the chia cho 0')
        else
    begin
        kq := a/b;
        write(a:0:3,' / ',b:0:3,' = ',kq:0:3);
    end;
end;

begin
    repeat
        clrscr;
        writeln(' - 0: Thoat');
        writeln(' - 1: cong hai so.');
        writeln(' - 2: tru hai so.');
        writeln(' - 3: nhan hai so.');
        writeln(' - 4: chia hai so.');
        write('  Chon phep tinh: '); readln(choose);
        case choose of 
            0: Thoat;
            1:cong;
            2:tru;
            3:nhan;
            4:chia
            else write('  Chon sai phep toan!')
        end;
        readln;
    until choose=0;
end.