Determine if NSString's first character is a number

Question

I just wanted to know how i can determine whether a NSStrings first character is a number.

Answer 1

BOOL hasLeadingNumberInString(NSString* s) {
if (s)
    return [s length] && isnumber([s characterAtIndex:0]);
else
    return NO;

}

In the event you are handling many NSStrings at once (like looping through an array) and you want to check each one for formatting like leading numbers, it's better practice to include checks so that you do not try evaluating an empty or nonexistent string.

Example:

NSString* s = nil; //Edit: s needs to be initialized, at the very least, to nil.
hasLeadingNumberInString(s);          //returns NO
hasLeadingNumberInString(@"");        //returns NO
hasLeadingNumberInString(@"0123abc"); //returns YES

Answer 2

Yes. You can do:

NSString *s = ...; // a string
unichar c = [s characterAtIndex:0];
if (c >= '0' && c <= '9') {
    // you have a number!
}

Answer 3

I can think of two ways to do it. You could use

[string rangeOfCharacterFromSet:[NSCharacterSet decimalDigitCharacterSet]].location == 0

Or you could use

[[NSCharacterSet decimalDigitCharacterSet] characterIsMember:[string characterAtIndex:0]]