Question

        Console.WriteLine("Are you a boy or a girl?");
        string sex = Console.ReadLine();
        Console.WriteLine(sex);
        while ((sex != ("boy")) && (sex != ("girl")))
        {
            Console.WriteLine("That is not a valid sex. Please answer the question again.");
            sex = Console.ReadLine();

        }

        if (sex == "boy")
        {
            Console.WriteLine("You are a boy");
            Boy real_sex = new Boy
            {
                Firstname = "George",
                Secondname = "Smith"
            };
        }
        else if (sex == "girl")
        {
            Console.WriteLine("You are a girl");
            Girl real_sex = new Girl
            {
                Firstname = "Charlotte",
                Secondname = "Smith"
            };
        }

        real_sex.Characteristics()

我是C＃的新手，所以这可能很容易，但我试图创建一个程序，询问用户的性别，然后根据“男孩”或“女孩”的答案为该课程创建一个实例。我已经在“男孩”和“女孩”类中创建了“特征”方法。但是，最后一行“real_sex.Characteristics（）”出现了问题，因为“当前上下文”中不存在“real_sex”。显然，要使用常规变量来克服这个问题，您需要在if语句之前声明变量，但是在实例中它似乎有不同的行为。有人可以帮忙吗？谢谢。

Answer 1

这是一个范围问题。在代码块中定义变量时，它不会存在于该代码块之外。例如：

int a = 2;
{
    int b = 3;
}
Console.WriteLine("A : " + a.ToString());
Console.WriteLine("B : " + b.ToString());

打印很好，但是在尝试打印B时会抛出错误，因为B是在打印语句之前结束的代码块中定义的。

解决方案是在相同（或更高）的代码块中定义所需的变量，而不是需要它们。比较：

int a = 2;
int b = 0;
{
    b = 3;
}
Console.WriteLine("A : " + a.ToString());
Console.WriteLine("B : " + b.ToString());

这样可以正常工作，现在打印A：2和B：3。

所以，改变

        if (sex == "boy")
        {
            Console.WriteLine("You are a boy");
            Boy real_sex = new Boy
            {
                Firstname = "George",
                Secondname = "Smith"
            };
        }
        else if (sex == "girl")
        {
            Console.WriteLine("You are a girl");
            Girl real_sex = new Girl
            {
                Firstname = "Charlotte",
                Secondname = "Smith"
            };
        }

        real_sex.Characteristics()

到

        Sex real_sex = null;
        if (sex == "boy")
        {
            Console.WriteLine("You are a boy");
            real_sex = new Boy
            {
                Firstname = "George",
                Secondname = "Smith"
            };
        }
        else if (sex == "girl")
        {
            Console.WriteLine("You are a girl");
            real_sex = new Girl
            {
                Firstname = "Charlotte",
                Secondname = "Smith"
            };
        }

        real_sex.Characteristics()

当然，您需要一个名为“Sex”的父类，从中派生男孩和女孩，这样您就可以将real_sex设置为男孩或女孩。

Answer 2

You have escope problem.
You need to declara the variable outside the if statement.  

If (){

Code and variables that only exist here can only run here 
//This method have to run here

Real_Sex.Characteristics();
Have to run here
}
Else {
Same here...
}
Or you can make a dynamic variable outside the scope



Console.WriteLine("Are you a boy or a girl?"); string sex = Console.ReadLine();
            dynamic real_sex;
            Console.WriteLine(sex); 
        while ((sex != ("boy")) && (sex != ("girl"))) 
    { 
    Console.WriteLine("That is not a valid sex. Please answer the question again."); 
        sex = Console.ReadLine(); }
         if (sex == "boy") {
         Console.WriteLine("You are a boy");
          real_sex = new Boy 
        { Firstname = "George", 
    Secondname = "Smith" }; 
    } 
        else if(sex == "girl") 
    { 
        Console.WriteLine("You are a girl"); 
             real_sex = new Girl
         { Firstname = "Charlotte", 
        Secondname = "Smith" }; 
    }
         real_sex.Characteristics();

C＃实例在当前上下文中不存在

2 个答案: