c# - 对分配的字符串使用未分配的局部变量错误

Question

所以，我是 C# 的初学者，我真的不知道为什么我会收到变量“name”的“使用未分配的局部变量错误”。我有这个简单的代码，它要求输入姓名，如果不是 Bob 或 Alice，它会显示一条消息。

using System;

namespace exercise2
{
    class Program
    {
        static void Main(string[] args)
        {
            string name;
            int i = 0;
            while (i == 0)
            {
                Console.Write("What is your name?\n>>> ");
                name = Console.ReadLine();
                if ((name == "Alice") || (name == "Bob"))
                {
                    i = 1;
                    Console.Clear();
                }
                else
                {

                    Console.WriteLine("You're not Alice or Bob.");
                    Console.ReadKey();
                    i = 0;
                    Console.Clear();
                }

            }
            Console.WriteLine("Good Morning, " + name); //"name" is unassigned
            Console.ReadKey();
        }
    }
}

希望这不是一个愚蠢的问题。

谢谢

Answer 1

这是因为编译器无法“看到”对 while() 语句的评估肯定是 true 并且 name 将在while 第一次阻塞。

改变你的

string name;

进入

string name = ""; //or string.Empty

虽然作为人类我们可以很容易地读到 while block 将第一次执行:

string name; //unassigned
int i = 0;
while (i == 0) //will enter
{
    Console.Write("What is your name?\n>>> ");
    name = Console.ReadLine(); //name will definitely be assigned here
    ... something else
}
Console.WriteLine("Good Morning, " + name); //compiler cannot "see" that the while loop will definitely be entered and name will be assigned. Therefore, "name" is unassigned

编译器看不到，因此给您错误。

或者，您也可以将 while block 更改为 do-while 以强制编译器看到 name 将被分配(归功于 Lee ):

string name; //unassigned
int i = 0;
do //will enter
{ 
    Console.Write("What is your name?\n>>> ");
    name = Console.ReadLine(); //name will definitely be assigned here
    ... something else
} while (i == 0);
Console.WriteLine("Good Morning, " + name); //should be OK now