You can add a zero before a number in Google Sheets and Excel using this tutorial. You need to change cell formatting or use function.

REPT function is a Text function, and its purpose is to repeat text a given number of times. Learn to use the Rept Function in Excel.

How to Insert a Combo Box in Excel 2010. Combo boxes are a useful way of entering data into an Excel spreadsheet, combining the flexibility of a text field with the convenience of a list box.