利用WPF窗口程序设计简单计算器

string num1 = null; //运算符之前的数
string num2 = null; //运算符之后的数
string ope = null; //运算符

private void button1_Click(object sender, RoutedEventArgs e)
 {
 if (ope == null)
 {
 num1 += button1.Content;
 textBox.Text = num1;
 }
 else
 {
 num2 += button1.Content;
 textBox.Text = num2;
 }
}

private void buttonADD_Click(object sender, RoutedEventArgs e)
 {
 ope = "+";
 }

private void buttonCE_Click(object sender, RoutedEventArgs e)
 {
 //if (ope == null)
 //{
 // num1 = textBox.Text;
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