How can I use variables in multiple files?

Question

I want do define a variable in the header and be able to use it in multiple files. e.g. have variable a defined somewhere and be able to use/change it in both

Answer 1

In the header file, write this:

extern int a;
extern float b;

This will declare the variables.

In one of the CPP files, write this:

int a = 1;
float b = 2.2;

This will define the variables. It does not matter in which CPP file you put the definitions, as long as the variables are defined exactly once.