strings in C#

Question

How can I check a string to make sure that it contains only numbers?

Scott Lysle · Answer

Well you can limit it to numbers and special characters with something like this: private void textBox5_KeyPress( object sender KeyPressEventArgs e) { // allows only special characters or numbers if ( char .IsLetterOrDigit(e.KeyChar) && char .IsLetter(e.KeyChar)) { e.Handled = true ; } } Or for just the items mentioned: private void textBox6_KeyPress( object sender KeyPressEventArgs e) { // allows only special characters or numbers if (e.KeyChar != '0' && e.KeyChar != '1' && e.KeyChar != '2' && e.KeyChar != '3' && e.KeyChar != '4' && e.KeyChar != '5' && e.KeyChar != '6' && e.KeyChar != '7' && e.KeyChar != '8' && e.KeyChar != '9' && e.KeyChar != '#' && e.KeyChar != '/' && e.KeyChar != '*' && e.KeyChar != '-' && e.KeyChar != '+' ) { e.Handled = true ; } } Aside from that you could check it against a regular expression using the .NET regular expression library methods.

Brad · Answer

Ok I liked the part about the handle but how do I now make it so it can only use these characters: 0123456789/*-+

Scott Lysle · Answer

If this returns false the string contains characters other than numbers. private bool StringHasNumbers( string testString) { char [] c = testString.ToCharArray(); for ( int i = 0; i { if ( Char .IsDigit(c[i])) { return true ; } } return false ; } You can also prevent the user from entering other than digits into a textbox easily enough by handling the keypress event for that textbox e.g.: private void txtDollarValue_KeyPress( object sender KeyPressEventArgs e) { // allows only numbers if (! char .IsNumber(e.KeyChar)) { e.Handled = true ; } }