Checking the format of characters within a postcode [closed]

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I am constructing a form and have managed to sort out the input in the form. What I am attempting to do is when an entry is inputed for the postcode it does a check to make sure it follows a pre determined format. So far I have removed the space, made 2 character sets, one with numerical values and one with just letters. And then done a check on the string length. This is below:-

NSCharacterSet *cset = [NSCharacterSet characterSetWithCharactersInString:@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"];
NSCharacterSet *nset = [NSCharacterSet characterSetWithCharactersInString:@"1234567890"];

_QuestionAnswer.text = [_QuestionAnswer.text stringByReplacingOccurrencesOfString:@" " withString:@""]; //removes the space character
if (4 < _QuestionAnswer.text.length < 8) //checks string length between 5 and 7
{
    // this is where the format check should be done using cset and nset
}

NB UK post codes must follow any one of the example formats below:-

AA9A 9AA,

A9A 9AA,

A9 9AA,

A99 9AA,

AA9 9AA,

AA99 9AA,

Where 'A' is from cset and '9' is from nset

Thank you in advance.

Answer 1

You can use regular expressions (my is just example):

NSString *laxString = @".+@([A-Za-z0-9]+\\.)";
NSPredicate *postCodeTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", laxString];

return [postCode evaluateWithObject: postCodeTest];