The ? character is the beginning of a conditional operator. It's an if, then statement. It is used like this:
condition ? result if condition is true : result if condition is false
Your statement says:
IF (GlobalNumberN - CountIDLimitMax) > 0 then
IF (GlobalNumberN + CountIDLimitMax) > CountIDLimitMax then
CountIDLimitMax + GlobalNumberN
but it is missing bolth ELSE statements which are started by the : symbol.
What exactly are you trying to do with this statement?