ISBN13 check digit: Difference between revisions
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assert(!isValidISBN13("978-1788399083"));
}</syntaxhighlight>
=={{header|Delphi}}==
{{works with|Delphi|6.0}}
{{libheader|SysUtils,StdCtrls}}
<syntaxhighlight lang="Delphi">
function ValidateISBN(ISBN: string): boolean;
{Validate an ISBN number}
var I,N,Sum: integer;
begin
Sum:=0;
{Go througha chars, ignoring non-digits}
for I:=1 to Length(ISBN) do
if ISBN[I] in ['0'..'9'] then
begin
N:=StrToInt(ISBN[I]);
{Every other digit multiplied by 3}
if (I and 1)=1 then N:=N*3;
{Sum digits}
Sum:=Sum+N;
end;
{The sum must be an even multiple of 10}
Result:=(Sum mod 10)=0;
end;
procedure ValidateAndShow(Memo: TMemo; ISBN: string);
{Validate ISBN number and show the result}
var S: string;
begin
S:=ISBN;
if ValidateISBN(ISBN) then S:=S+' (Good)'
else S:=S+' (Bad)';
Memo.Lines.Add(S);
end;
procedure TestISBNSet(Memo: TMemo);
{Test supplied set of ISBN numbers}
begin
ValidateAndShow(Memo,'978-0596528126'); //(good)
ValidateAndShow(Memo,'978-0596528120'); //(bad)
ValidateAndShow(Memo,'978-1788399081'); //(good)
ValidateAndShow(Memo,'978-1788399083'); //(bad)
end;
</syntaxhighlight>
{{out}}
<pre>
978-0596528126 (Good)
978-0596528120 (Bad)
978-1788399081 (Good)
978-1788399083 (Bad)
</pre>
=={{header|Draco}}==
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