Questions about whiptail and bash functions

I'm a bash newbie.

• How to make whiptail full terminal screen? "as big as the terminal", like fluid CSS


• Say I have this script

   #!/bin/bash

function cpp-lang {  
yum install "Development Tools"  
}
function updatesys { 
yum -y update yum -y upgrade
}

     whiptail --checklist "test" 5 40 5\
                Update "Update the system" on \
                C++ "Install C++" off 2>results 

while read choice 
do
      case $choice in
        Update )updatesys
         ;;
        C++)cpp-lang
         ;;
         *)
         ;;
         esac
         done < results

When I run it, it exists, should I return something from the function?

• Considering the script above as an example, should I run sudo everytime I call yum install or is doing sudo ./script.shenough?