length$(),$charAt$($index$),$trim$()$

explain how above be used in a program for input validation $(1-3$ sentences each$).$

$$ Input validation is when we analyze user input and check if it is valid based on

predetermined rules.

$$ Input validation could also modify input to follow a specific format $($ex$.$ Phone number

$1234567890$ being modified to $(123)456-7890).$

Q$6$