— Scheme Procedure: number->string n [radix]
— C Function: scm_number_to_string (n, radix)

Return a string holding the external representation of the number n in the given radix. If n is inexact, a radix of 10 will be used.

— Scheme Procedure: string->number string [radix]
— C Function: scm_string_to_number (string, radix)

Return a number of the maximally precise representation expressed by the given string. radix must be an exact integer, either 2, 8, 10, or 16. If supplied, radix is a default radix that may be overridden by an explicit radix prefix 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, then string->number returns #f.

— C Function: SCM scm_c_locale_stringn_to_number (const char *string, size_t len, unsigned radix)

As per string->number above, but taking a C string, as pointer and length. The string characters should be in the current locale encoding (locale in the name refers only to that, there's no locale-dependent parsing).