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    <p>The last digit of ISBN-10 is the check digit. Since your method is supposed to check if the entered ISBN is correct, you have to calculate the check digit on your own and compare it to the given one (plus making sure all characters are digits).</p> <p>If you're not knowing what this means, read the validating ISBN-10 section at <a href="http://en.wikipedia.org/wiki/International_Standard_Book_Number#Check_digits" rel="nofollow">http://en.wikipedia.org/wiki/International_Standard_Book_Number#Check_digits</a> </p> <blockquote> <p>The 2001 edition of the official manual of the International ISBN Agency says that the ISBN-10 check digit[18] — which is the last digit of the ten-digit ISBN — must range from 0 to 10 (the symbol X is used instead of 10) and must be such that the sum of all the ten digits, each multiplied by the integer weight, descending from 10 to 1, is a multiple of the number 11. Modular arithmetic is convenient for calculating the check digit using modulus 11. Each of the first nine digits of the ten-digit ISBN — excluding the check digit, itself — is multiplied by a number in a sequence from 10 to 2, and the remainder of the sum, with respect to 11, is computed. The resulting remainder, plus the check digit, must equal 11; therefore, the check digit is 11 minus the remainder of the sum of the products.</p> </blockquote> <p>On a related note: there is also the 13-digit ISBN-13...</p> <p>Maybe your solution might look like this:</p> <p>Remove the dashes, break down the <code>string</code> to an <code>int</code> array, compute the tenth-digit (see wiki-link), if all is fine return the input string.</p>
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    1. POAnother question, this time regarding breaking a string down for validity
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    1. POAnother question, this time regarding breaking a string down for validity
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    1. COyeah, I'm going to code a separate checkDigit() method later, I just want to ensure I am doing this part right first.
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    2. CO@unit -- i included a hint in my answer.. this will make things easier. If you surround it in a try-catch statement and a digit is not parsable as int, the check fails.
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    3. COnice thanks for the tip. Forgot that i have to add it to an int array, had it going into a string
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