If s cannot be parsed, then ok will be false

Most Pascal dialects do not come with a built-in big integer library.
Most "3rd-party" big integer implementations for Pascal (or Delphi) simply overload the assignment operator, as in the example.
The ncalc library raises an exception if s is not a valid big integer.
s may also be a hexadecimal, octal or binary representation.

The type int is unbounded

This raises an exception if s is invalid

Extraneous characters past the end of a valid number are ignored. If there is not a valid number at the start of s, 0 is returned. This never raises an exception.