这是一个简单的计算器程序，分别输入左操作数和右操作数，并选择运算符以后，就能计算出结果。如果输入不合法，就会显示错误信息。-This is a simple calculator program, enter the left operand and the right operand, and select an operator will be able to calculate the results. If the input is not legitimate, it will dis