设计一个简易的计算器，可以进行四则运算：加、减、乘、除等（限于十进制下）

要求：

1.操作符号定为：“+”，“-”，“*”，“/”，“(”,“)”等。（按国际惯例设计）

2.用户通过点击面板中的各种组件输入的表达式，应在上方文本框中显示。

3.当用户点击“=”时，文本框中之前的内容应清空，直接显示表达式运算结果。例如：输入表达式“3+2*（8-5）”之后按“=”，显示结果“9”。

4.具有菜单栏，内有相应的编辑“复制”、“粘贴”等菜单，提供相应的功能。

-Design a simple calculator that can be four operations: addition, subtraction, multiplication, division, etc. (limited to the decimal) requirements: 1 Operating symbol as:. " Ppls" , " -" , " *" , " /" , , " (" , " )" , etc. (According to international practice design) 2. Users clicking through the various components of the panel input expression should be displayed above the text box. 3 When the user clicks the " =" , the previous contents of the text box should be emptied directly display expression calculation result. For example: Enter the expression " 3+2* (8-5)"　then press " ="　to display the results of " 9."　4 has a menu bar, the corresponding edit " Copy" , " Paste"　and other menus, provide the appropriate functionality.