Numerical input and output

Procedure: number->string z [radix]

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

(let ((number number)
      (radix radix))
  (eqv? number
        (string->number (number->string number radix)

is true. It is an error if no possible result makes this expression true.

If present, radix must be an exact integer in the range 2 to 36, inclusive. 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; 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.

Procedure: string->number string [radix]

Returns a number of the maximally precise representation expressed by the given string. It is an error if radix is not an exact integer in the range 2 to 26, inclusive.

If supplied, radix is a default radix that will be overridden if an explicit radix prefix is present in the 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.

(string->number "100")      ⇒  100
(string->number "100" 16)   ⇒  256
(string->number "1e2")      ⇒  100.0
(string->number "#x100" 10) ⇒  256