'overflow: Let say, you use _UNSIGNED _BYTE type variable. This type maximum value is 255. What, if this value is bigger?
DIM a AS _UNSIGNED _BYTE
a = 255
PRINT a
a = 256
PRINT a
'as you see, second value is not 255, but 0. Its, because QB64 test it and return this value after overflow back to begin.
a = 255 * 2 'return 254 - because 255 * 2 = 510 = 510 - 256 = 254. Zero is as 1.
PRINT a
'so for testing it, you muss know variable type and maximum value, which can be used for this variable type.