mouse.x refers to an undefined (user defined type?) variable. If "mouse.x" was a symbol that was associated with a value of 5, you would need to assign it to a string variable, then you could search the symbol with instring() to find its components. From this you could work out the value 5.
a+c concatenates the strings just like the operator a&c does.
Seriously, why might you want to do this? Would it not be easier just to
@pritchard: Neither, possibly both.
This attempt to apply run-time output of a program to the compile-time symbol table management hits the problem of reverse time travel. cha0s was quite correct.
Even if FreeBASIC was an interpreter, the syntax and structure of the language precludes such things.
After considering a few possibilities it appeared to be necessary to either write a program to generate and compile another program file or to implement some code to manage a symbol table based solution. My code resulted from the logical elimination of other possibilities.
A competent bureaucrat or politician will not hold an inquiry without first being certain of the required outcome. The client clearly specified the outcome. There was no other simple way. My code was intended not so much a joke as an admission of defeat.