简单的GUI程序 建一个小型的计算器, 是一个简单的GUL, 具有以下元素 (1) 数字键 1, 2, 3 (2) 清除显示键C (3) 显示窗口 -A simple GUI program to build a small calculator, is a simple GUL, have the following elements (1) the number keys 1, 2, 3 (2) clear th