我的这个计算器，在不输入的时候，点计算会无法执行

Question

private void btnJiSuan_Click(object sender, EventArgs e)
        {
            if (txtNum1.Text == "")
            {
                MessageBox.Show("请输入第一个数", "提示", MessageBoxButtons.OK, MessageBoxIcon.Stop);
                this.txtNum1.Focus();
                return;
            }
            else if (cboYunSuan.Text == "")
            {
                MessageBox.Show("请输入运算符", "提示", MessageBoxButtons.OK, MessageBoxIcon.Stop);
                this.cboYunSuan.Focus();
                return;
            }
            else if (txtNum2.Text == "")
            {
                MessageBox.Show("请输入第二个数", "提示", MessageBoxButtons.OK, MessageBoxIcon.Stop);
                this.txtNum2.Focus();
                return;
            }
            else
            {            }            double num1 = double.Parse(txtNum1.Text.Trim());
            double num2 = double.Parse(txtNum2.Text.Trim());
            double result = 0;            if (cboYunSuan.Text == "+")
            {
                result = num1 + num2;
                txtJieGuo.Text = Convert.ToString(result);
            }
            else if (cboYunSuan.Text == "-")
            {
                result = num1 - num2;
                txtJieGuo.Text = Convert.ToString(result);
            }
            else if (cboYunSuan.Text == "*")
            {
                result = num1 * num2;
                txtJieGuo.Text = Convert.ToString(result);
            }
            else if (cboYunSuan.Text == "/")
            {
                result = num1 / num2;
                txtJieGuo.Text = Convert.ToString(result);
            }
            else if (cboYunSuan.Text == "%")
            {
                result = num1 % num2;
                txtJieGuo.Text = Convert.ToString(result);
            }
            else
            {
                MessageBox.Show("对不起暂不支持！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
        }

Answer 1

2楼已经找出原因了
代码不够严密。txtNum1.Text == ""。这个我敲个空格进去就崩溃了吧。输入的值也没进行异常处理