Limit number of characters is string

Question

How can I allow the user to enter a string with specific length?

Ex

Input 3
The user can write only ...
three characters

Answer 1

U can display error message "read the instructions carefully"

Answer 2

You can either reject input longer or shorter than 3 characters, or automatically cut/fill it to 3.

Answer 3

I don’t want to reject the input I want to store the strings in array but all the strings must have length that already defined by the user