Check that string contains only numeric values (number 0-9).

+(BOOL) validateStringContainsNumbersOnly:(NSString*)strng

{

    NSCharacterSet *s = [NSCharacterSet characterSetWithCharactersInString:@"1234567890"];

    s = [s invertedSet];

    //And you can then use a string method to find if your string contains anything in the inverted set:

    NSRange r = [strng rangeOfCharacterFromSet:s];

    if (r.location != NSNotFound) {

        NSLog(@"the string contains illegal characters");

        return NO;

    }

    else

        return YES;

}