并非所有代码路径都返回一个值，用于循环

Question

此代码将比较存储在文本文件中的用户名和密码 。 我认为这是因为for循环，它可能很简单，但我看不到它。

public int loginCheck()
{ 
    //-----------------------------------------------------------------
    string[] users = File.ReadLines("Username_Passwords").ToArray();
    //line of text file added to array 
    //-----------------------------------------------------------------

    for (int i = 0; i < users.Length; i++)
    {
        string[] usernameAndPassword = users[i].Split('_');
        //usernames and passwords separated by '_' in file, split into two strings

        if (_username == usernameAndPassword[0] && _password == usernameAndPassword[1])
        {
            return 1;
            //return 1, could have used bool
        }
        else
        {
            return 0;
        }
    }

Answer 1

如果users为空数组，则不返回任何值。

string[] users = File.ReadLines("Username_Passwords").ToArray();

// if users is empty, users.Length == 0 and the loop isn't entered
for (int i = 0; i < users.Length; i++) 
{
   ...
}  

// no value is returned 

return 0; // <- suggested amendment

可能您必须加上return 0; 在循环之下

作为进一步的改进，您可以使用Linq重新编写该方法（如果文件包含具有所需用户名和密码的 任何记录，则返回1否则返回0 ）：

public int loginCheck() {
  return File
    .ReadLines("Username_Passwords")
    .Select(line => line.Split('_'))
    .Any(items => items.Length >= 2 && 
                  items[0] == _username &&
                  items[1] == _password) 
   ? 1
   : 0;
}

Answer 2

您必须添加return 0; 循环后，如果用户的大小为0，则不会返回返回块。

    public int loginCheck() {
        //-----------------------------------------------------------------
        string[] users = File.ReadLines("Username_Passwords").ToArray();
        //line of text file added to array 
        //-----------------------------------------------------------------
        for (int i = 0; i < users.Length; i++) {
            string[] usernameAndPassword = users[i].Split('_');
            //usernames and passwords separated by '_' in file, split into two strings

            if (_username == usernameAndPassword[0] && _password == usernameAndPassword[1]) {
                return 1;
                //return 1, could have used bool
            }
        }
        return 0;
    }