In this case the equivalent is the combination of global variables + function which takes no arguments and returns void.
May-be there's a reason why you are doing this. C++ supports many programming paradigms, including unstructured programming (a.k.a. spaghetti code), however the minimum you should strive for - should you ever want to program in C++, not just port code from Basic - is structured procedural programming. That means, no GOTO (except perhaps very rare cases) and no GOSUB equivalents and no global variables (unless there's a good reason).
//considered harmful normally
int a, b;
//Gosub code goes here