How do I prevent users from entering decimals in a number field?

Under the number question's configuration, toggle on "Answer must be a whole number." This will prevent someone from being able to type in decimal.

Click on the question in the editor, then click the toggle in the configuration panel to the right.

Screenshot of a Number question from the editor. Answer must be a whole number is highlighted.

Toggle on "Answer must be a whole number."

Related Articles

How do I add a number question to my form?
On a blank line, type "/number" and select "Number" from the popup menu, or click "Add questions" and select "Number" from the question dropdown.
How can I make a number field be formatted like a price?
Configure the question, then set the number input formatting to "currency."