Regular expression for ios
-(BOOL)textField:(UITextField*)textField shouldChangeCharactersInRange:(NSRange)r replacementString:(NSString*)s
{
  NSCharacterSet * reject = [[NSCharacterSet characterSetWithCharactersInString:@"QWERTYUIOPASDFGHJKLZXCVBNMqwertyuiopasdfghjklzxcvbnm1234567890-&"] invertedSet];
  if ([s rangeOfCharacterFromSet:reject].length)
  {
    return NO;
  }
  return YES;
}

NSMutableCharacterSet *legalCharacters = [NSCharacterSet alphanumericCharacterSet];
[legalCharacters addCharactersInString:@"-&"];
NSCharacterSet *illegalCharacters = [legalCharacters invertedSet];

NSString *testString = @"ThisStringWillFail@#$%";

if ([testString rangeOfCharacterFromSet:illegalCharacters].location == NSNotFound) {
    // string passed validation
} else {
    // string failed validation
}