There are several ways to validate a string. In the example below we have a string that should be a Social Security Number.
It should have a length of 9 and consist entirely of digits.
Build the form as shown:
Test various different values. Try enough variations so that you are sure it works.
private void btnOK_Click(object sender, EventArgs e) { // Check if the input is a valid Social Security number, ie. 9 digits. String s = txtInput.Text; // Assume the string is valid until you find it to be invalid. Boolean ok = true; if (s.Length != 9) ok = false; else { // Convert the string to an array of characters. char[] chars = s.ToCharArray(); // Check that each character is a digit. for(int i=0;i<9;i++) { if (chars[i] < '0' || chars[i] > '9') ok = false; } } // Display the results. if (ok) lblOutput.Text = "That is a valid Social Security Number"; else lblOutput.Text = "That is NOT a valid Social Security Number"; } }
Experiment: How would you allow the 2 dashes: 314-15-9265?
How would you make it accept either with or without the dashes: 314159265 or 314-15-9265?