Objective c 函数的隐式声明'；如果'；是否在C99中无效？

我试图为我的应用程序创建一个注册页面，当我创建“如果”语句时，我遇到了一个C99错误。我使用的是xCode 5.1.1，我使用的是parse SDK和框架。我不太清楚我做错了什么，但如果这是一个非常明显的错误，我道歉

- (IBAction)continueAction:(id)sender {
    [_usernameField resignFirstResponder];
    [_emailField resignFirstResponder];
    [_passwordField resignFirstResponder];
    [_retypeField resignFirstResponder];
    [self checkFieldsComplete];
}

- (void) checkFieldsComplete {
    If ([_usernameField.text isEqualToString:@""] || [_emailField.text isEqualToString:@""] || [_passwordField.text isEqualToString:@""] || [_retypeField.text isEqualToString:@""]); { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Woaaahhhh, hold on there" message:@"You must complete all fields" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
    }
     {
        [self checkPasswordsMatch];
    }

}

- (void) checkPasswordsMatch {
    if (![_passwordField.text isEqualToString:_retypeField.text]) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Woaaahhhh" message:@"Passwords don't match" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
    }
    else {
        [self registerNewUser];
    }
}

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问题出在这一行：

If ([_usernameField.text isEqualToString:@""] || [_emailField.text isEqualToString:@""] || [_passwordField.text isEqualToString:@""] || [_retypeField.text isEqualToString:@""]); { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Woaaahhhh, hold on there" message:@"You must complete all fields" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];

将

If

重命名为

If

。C关键字和标识符区分大小写。另外，删除if语句后的分号。如果希望在if语句为false时执行第二个块，则还需要插入

else

。总的来说，它应该是这样的：

if ([_usernameField.text isEqualToString:@""] || [_emailField.text isEqualToString:@""] || [_passwordField.text isEqualToString:@""] || [_retypeField.text isEqualToString:@""])
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Woaaahhhh, hold on there" message:@"You must complete all fields" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
}
else
{
    [self checkPasswordsMatch];
}

---

非常感谢。我知道这是一个明显的错误。我想我需要多加注意