IF语句的应用

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Label1: TLabel;
    Label2: TLabel;
    Edit1: TEdit;
    Edit2: TEdit;
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Edit1KeyPress(Sender: TObject; var Key: Char);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);                   //“确定”按钮
var
  w,x: real;
begin
  if edit1.Text = '' then edit1.Text := '0';                      //防止Edit1为空引发的错误
  w := strtofloat(edit1.Text);
  if w<=50 then                                                   //IF的复合语句
    x := 0.25 * w
  else
    if w <= 100 then
      x := 0.25 * 50 + 0.35 * (w-50)
    else
      x := 0.25 * 50 + 0.35 * 50 + 0.45 * (w-100);
  edit2.Text := floattostr(x);
  edit1.SelStart :=0;
  //SelStart－返回或设置所选择的文本的起始点；如果没有文本被选中，则指出插入点的位置。
  edit1.sellength := length(edit1.Text);
  //SelLength－返回或设置所选择的字符数
end;

procedure TForm1.Button2Click(Sender: TObject);                   //“清除”按钮
begin
  edit1.Text := '';
  edit2.Text := '';
end;

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);   //防止非法键输入代码
var
  l: boolean;
begin
  l := (key=#8) or (key=#46) or ((key>#47) and (key<#58));
  //#8为BackSpace键，#46为“.”键，#48到#57为数字键
  if NOT l then key := #0;
  //屏蔽输入除数字键，BackSpace键和“.”键以外的键
end;

end.