Numerical input and output

It is an error if radix is not one of 2, 8, 10, or 16.
The procedure number->string takes a number and a radix and returns as a string an external representation of the given number in the given radix such that is true. It is an error if no possible result makes this expression true. If omitted, radix defaults to 10.
If z is inexact, the radix is 10, and the above expression can be satisfied by a result that contains a decimal point, then the result contains a decimal point and is expressed using the minimum number of digits (exclusive of exponent and trailing zeroes) needed to make the above expression true [4, 5]; otherwise the format of the result is unspecified.
The result returned by number->string never contains an explicit radix prefix.
Note: The error case can occur only when z is not a complex number or is a complex number with a non-rational real or imaginary part.
Rationale: If z is an inexact number and the radix is 10, then the above expression is normally satisfied by a result containing a decimal point. The unspecified case allows for infinities, NaNs, and unusual representations.

Returns a number of the maximally precise representation expressed by the given string. It is an error if radix is not 2, 8, 10, or 16.
If supplied, radix is a default radix that will be overridden if an explicit radix prefix is present in string (e.g. "#o177"). If radix is not supplied, then the default radix is 10. If string is not a syntactically valid notation for a number, or would result in a number that the implementation cannot represent, then string->number returns #f.
An error is never signaled due to the content of string.
Note: The domain of string->number may be restricted by im- plementations in the following ways. If all numbers supported by an implementation are real, then string->number is permit- ted to return #f whenever string uses the polar or rectangular notations for complex numbers. If all numbers are integers, then string->number may return #f whenever the fractional nota- tion is used. If all numbers are exact, then string->number may return #f whenever an exponent marker or explicit exact- ness prefix is used. If all inexact numbers are integers, then string->number may return #f whenever a decimal point is used.
The rules used by a particular implementation for string->number must also be applied to read and to the routine that reads programs, in order to maintain consistency between internal numeric processing, I/O, and the processing of programs. As a consequence, the R5RS permission to return #f when string has an explicit radix prefix has been withdrawn.