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Checking Whether a String Is a Valid Number

Problem

You need to check if a given string contains a valid number.

Solution

We supose that we want to check the next strings: "42", "2+3i", "3.1416", "2/3", "hello". First, we're going to try to convert that string to a number, and then we're going to pass the result to the predicate number? which is defined in Scheme. Let's see some examples:

(number? (string->number "42"))
(number? (string->number "2+3i"))
(number? (string->number "3.1416"))
(number? (string->number "2/3"))
(number? (string->number "hello"))

Discussion

There may also be times when you want to tell if a given number is an integer number a floating-point number. One solution is using the procedure string->number, and then we can use one of the next procedures:

(complex? (string->number "3+4i"))
(real? (string->number "#e1e10"))
(rational? (string->number "6/10"))
(integer? (string->number "3.0"))

Contributors

-- ChandraQuintas - 27 Apr 2004