C# Code, not working else statement

i am beginner programmer who is creating a hangman game so i am going to show you codes that's i used and which one is not working.

    string target;
    public int attempt = 0;

     public void firststage()
    {
        pictureBox1.Image = Image.FromFile(@"C:\Users\OmarS_000\Documents\Visual Studio 2015\Projects\HangMan\HangMan\stage1.png");
        attempt++;
    }

   private void buttonZ_Click(object sender, EventArgs e)
    {
        matching('z');     
    }

now the code which is not working.

   public void matching(char _thechar)
    {
        if (target.Contains(_thechar))
        {
            MessageBox.Show("Corret");
        }
        else
        {                
            switch (attempt)
            {                   
                case (0):
                    firststage();
                    break;

                case (1):
                    secondstage();
                    break;

                case (2):
                    thirdstage();
                    break;

                case (3):
                    fourthstage();
                    break;

                case (4):
                    fifthstage();
                    break;

                case (5):
                    death();
                    break;
            }
        }
    }

the code works if the letters exist it shows the MessageBox Correct. but if the letter z didn't exist in string target it does nothing. i even tried replacing displaying the picture with messagebox but it didn't work too. PS: target is a string which gets a random word from an array.

so to make it clear. how can i make the code works.