title: Check the textbox contains any characters and numbers
body: <p>I wanted to make where the text in the textbox entered by user, have to contains characters followed by numbers. Example: A1001. I already found a solution using the Regex and show an error message box if the textbox not contains characters followed by number, but once I entered the text "A1" in the textbox, the error message box still appear.</p>
  
  <p>Here is the code that I am using:</p>
  
  <pre><code>void button1_Click(object sender, EventArgs e)
          {
              if (!Regex.IsMatch(this.textBox1.Text, @"(a-zA-Z)"))
              {
                  SystemManager.ShowMessageBox("Please enter the characters followed by the numbers for the product code. \nExample: A1001", "Information", 2);
              }
  
              else if (!Regex.IsMatch(this.textBox1.Text, @"(0-9)"))
              {
                  SystemManager.ShowMessageBox("Please enter the characters followed by the numbers for the product code. \nExample: A1001", "Information", 2);
              }
          }
  </code></pre>
  
  <p>Your answer very much appreciated!</p>
  
  <p>Thank you</p>