The int in front of the r = param.asInt() is telling the code to keep this version of the r integer variable local to the BLYNK_WRITE(V0) function.
If you want the value of r that is being modified by the slider on V0 to be visible to the rest of your code (which you do) then remove the int from this line of code.
If you want to understand more about this then google “variable scope in C++”.
Pete.