user ha scritto: > Hi i check the overflow of variables and there is something i dont > understand. > > My system is > > u...@ubuntu-desktop:~$ cat /etc/*release* > DISTRIB_ID=Ubuntu > DISTRIB_RELEASE=10.04 > DISTRIB_CODENAME=lucid > DISTRIB_DESCRIPTION="Ubuntu 10.04.1 LTS" > > Linux ubuntu-desktop 2.6.32-25-generic #45-Ubuntu SMP Sat Oct 16 > 19:52:42 UTC 2010 x86_64 GNU/Linux > > > > I have this small code > ----------------------------------- > ' Gambas class file > PUBLIC SUB Form_Open() > > DIM bVar AS Boolean = TRUE > DIM iNum AS Byte = 255 > DIM iA AS Short = 32767 > DIM iRoads AS Integer = 2147483647 > DIM iBig AS Long = 9223372036854775807 > DIM iArea AS Single = 1.7014118E+38 > DIM fPi AS Float = 8.98846567431105E+307 > > bVar += 1 > iNum += 1 > iA += 1 > iRoads += 1 > iBig += 1 > iArea += 1 > fPi += 1 > > PRINT bVar > PRINT iNum > PRINT iA > PRINT iRoads > PRINT iBig > PRINT iArea > PRINT fPi > > END > ----------------------------------- > > And i get the following result > > False > 0 > -32768 > -2147483648 > -9223372036854775808 > 1.701411834605E+38 > 8.988465674311E+307 > > > My question is why the Single and Float do not overflow? > Because they should not overflow, I think. "Real" numbers (in the IT sense: "float" if you prefer ) are not discrete numbers, they have a limited precision; a single bit pattern in a float corresponds to infinite numbers in the real world. When you add a very small quantity to a float (and "1", compared to 1E+38, is very small), you simply tell it to store a different number, which has the same bit representation. If a float would overflow, it would cease its main reason to exist: in most situations you *do* want it to behave so. You could add a bigger number to make it overflow: you should add a number big enough to fall in the precision bits of the mantissa. A normal float has perhaps 6/7 digits of precision; to choose a comparable a number, you should choose something like 1E+31 (this "1" falls in the digits of precision of 1E+38). But! Even in that case, the number should not overflow, but raise an error (overflow error). This last thing depends on implementation of the floating point by the host computer.
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