如果用户多次输入无效的用户名和密码，如何终止程序

Question

The problem in this code is that it doesn't terminate the program even though I clicked the login button with a invalid username and password 3 times. So what I want to happen is that when the user inputs a invalid username and password 3 times, it will terminate the program.

MessageBox.Show("Invalid username and/or password.");
pass_txt.Text = null;

int login_count = 0;
login_count = login_count + 1;
if (login_count == 3)
{
    Application.Exit();
}

Answer 1

int login_count = 0;
login_count = login_count + 1;

Login_count will never be greater than 1, since you initialize it to 0 right before you increment it. You need to make it global, then increment it without setting it back to 0.

You'll need something closer to

if(failedLogin)
{
    // ...
    this.login_count++;
}

// ...
if (this.login_count == 3)
{
    Application.Exit();
}

Answer 2

Something like this might work.

    private void Login()
    {
        int login_count = 0;
        bool goodLogin = false;
        do
        {
            if (DoLogin())
                goodLogin = true;
            else
                login_count++;

        } while (login_count < 4 && !goodLogin);

        if (goodLogin)
        {
            //do the login stuff
        }
        else
        {
            Application.Exit();
        }
    }

    private bool DoLogin()
    {
        if (true) //do the login logic here
            return true;
        else
        {
            MessageBox.Show("Invalid username and/or password.");
            pass_txt.Text = null;
            return false;
        }
    }