+ - * / =之类的怎么写               

就是一个Button，把text设置为+,-,*,/，按相应的键，执行相应的运算！

btnAdd.Click += button_Click;
btnSub.Click += button_Click;
btnMul.Click += button_Click;
btnDiv.Click += button_Click;


void button_Click(object sender, EventArgs e)
{
    switch(((Button)sender).Text)
    {
        case "+":
            ...
            break;
        case "-":
            ...
            break;
        case "*":
            ...
            break;
        case "/":
            ...
            break;
        default:
            break;
    }
}