public void RecordSign(string sign)//定义函数
        {
            FirstInput = true;
            
            if (LastSign == "")
            {
                OperandA = Convert.ToDouble(txtResult.Text);

            }
            else
            {
                operations();
                txtResult.Text = OperandA.ToString();
            }

            LastSign = sign;
        }
        private void btnPlus_Click(object sender, EventArgs e)
        {
            RecordSign("+");
        }
        private void btnSub_Click(object sender, EventArgs e)
        {
            RecordSign("-");
        }
        private void btnMul_Click(object sender, EventArgs e)
        {
            RecordSign("*");
        }
        private void btnDiv_Click(object sender, EventArgs e)
        {
            RecordSign("/");
        }
         请求 定义函数 中代码的解释；；；；；
       感谢！！！！！！1

public void operations()
        {
            switch (LastSign)
            {
                case "+": OperandA += OperandB; break;
                case "-": OperandA -= OperandB; break;
                case "*": OperandA *= OperandB; break;
                case "/": OperandA /= OperandB; break;
                default:
                    break;
            }
        }


    谢谢有心人，对了 就是这个、、、