Mutable Borrow

Write a function called add_exclaim that takes a mutable borrow of a String and appends "!" to it. Call it twice on the same string, then print the result.

Expected output:

Wow!!

Hints:

• The function signature: fn add_exclaim(text: &mut String)
• Use text.push_str("!") to append
• The variable must be declared with let mut
• Pass it with &mut my_string