>What is the advantage of using constantes rather the public variables ?


Constants are BUILT-IN during the compilation time.
You CAN'T change them. You ever will get and error message if you want to :-)
(I really missed CLIPPER Case-sensitive #define compilation)

Try this:

#define TEST "MyTest"
MessageBox(TEST)
TEST = "TestMe" && BOOM even before you start the program (if you have set "Compile before saving" to true)
MessageBox(TEST)
test = 12       && BOOM even before you start the program (if you have set "Compile before saving" to true)
MessageBox(TEST)

Compilator just find ALL instances of left part of the define class in current routine and change it to the right part of it.
So in that example AFTER compilation VFP will execute this (and that is the actual code in your EXE):

MessageBox("MyTest")
"MyTest" = "TestMe"
MessageBox("MyTest")
"MyTest" = 12
MessageBox("MyTest")