Read this about floating point. The greatest possible integer will depend on the platform; typically it will be 2^64-1 or 2^32-1 for unsigned ints or 2^31-1 or 2^63-1 for signed integers. There may be odd machines that are neither 32 nor 64 bit or don't use twos-complement arithmetic(the Univac 1108 used 48 bit integers and ones-complement arithmetic); these will have different values.