Windows cmd script to convert a string to upper case

@echo off
setlocal enableextensions enabledelayedexpansion
set myvar=Jack_and-Jill_went-uP-the_hill.
echo/'myvar' is initially as follows:
echo/[%myvar%]
set UCase=ABCDEFGHIJKLMNOPQRSTUVWXYZ
set LCase=abcdefghijklmnopqrstuvwxyz
for /L %%A in (0,1,24) do Call :ToUpper !LCase:~%%A,1! !UCase:~%%A,1!
echo/
echo/And now that we're done, 'myvar' is as follows:
echo/[%myvar%]
goto :EOF
:ToUpper Low Up
set myvar=!myvar:%1=%2!