北航软院2014级C#期末考试部分考题解答

博主注：本渣渣水平有限，文中若有不对的地方敬请指出，谢谢。

本文中大部分图片来自老师的PPT，感谢邵老师，想要的可以点击右边QQ联系我：）

一、选择

6.Which of the following is wrong?

①Abstract class could contain non abstract method//抽象类可能没有抽象方法

②A class containing abstract method must be a abstract class.//含有抽象方法的类一定是抽象类

③An abstract class cannot be instantiated.//不能实例化

④An abstract class can be sealed class.

解答：基础知识

7. Which of the following is right use of generic?

①List<int> f = new List<int>()

②List<int> f = new List()

③List f = new List()

④List<int> f = new List<int>

解答：通用类的使用方法

8.Which of the statements is correct to declare a two-dimensional array in C#?

①int[][] a

②int a[][]

③int[2]a

④int a[2]

解答：创建数组

            //一维
            int[] a = new int[3];
            int[] b = new int[] { 3, 4, 5 };
            int[] c = { 3, 4, 5 };

            //非矩阵二维数组
            //int wrong1[1][2];//错误
            
            int[][] aa = new int[2][];// array of references to other arrays
            aa[0] = new int[] { 1, 2, 3 };// cannot be initialized directly
            aa[1] = new int[] { 4, 5, 6 };

            //矩阵二维数组
            int[,] aaa = new int[2, 3];// block matrix
            int[,] bbb = { { 1, 2, 3 }, { 4, 5, 6 } };// can be initialized directly
            int[,,] ccc = new int[2, 4, 2];

View Code

9.A property’s ______ accessor enable a client to modify the value of the instance variable associated with the property.

①base ②this ③get ④set

10. Only the methods that are declared as ______ can be overridden in subclass.

①abstract ②virtual ③new ④override

15. In .NET Framework class library, all multithread application related classes are in which following namespace?

①System.SysThread

②System.Thread

③System.Threading

④NetException

17. In C# variables confined by which of the following modifies can only be accessed by the current assembly?

①public ②protected ③internal ④private

解答：

17.Which of the following is the right output?

using System;
class A
{
    struct Student
    {
        public int age;
        public string name;
        public Student(int age,string name)
        {
            this.age = age;
            this.name = name;
        }
    };

    static void Main(string[] args)
    {
        Student stu1 = new Student(18, " Tom");
        Student stu2 = new Student(24, " Jerry");
        stu2 = stu1;
        stu1.age = 30;
        stu1.name = "Jerry";
        Console.Write(stu2.age);
        Console.Write(stu2.name);

        Console.ReadKey();
    }
}

View Code

①18 Tom ②18 Jerry ③30 Jerry ④30 Tom

解答：结构体实值类型，赋值之后就把<18,Tom>给了stu2，不管你stu1怎么变，与stu2无关。

18. Which of the following results is the right output?

ArrayList arr = new ArrayList();
int[] num = { 1, 3, 5 };
for (int i = 0; i < num.Length; i++)
{
　　arr.Add(num[i]);
}
arr.Insert(1, 4);
Console.WriteLine(arr[2]);

①1 ②3 ③4 ④5

解答：了解insert函数的定义就知道啦。

19.Which of the following description is true about the keyword “ref”?

①”ref” only passes values from caller(调用者)to callee(被调者)

②”ref” only passes values from the callee to caller

③”ref” must be initialized before its method is called.//方法被调用之前,必须初始化

④None of above

解答：VS爸爸最厉害~

20.Which of the following description about constants is true?

①Declare the constants with the keyword “static”

②The constants must be initialized when declaring.

③Constants can be assigned repeatedly.

④Constants can be declared first and assigned later.

解答：常量的基本知识

二、判断

1.Only one method can be called using a delegate.

解答：（F）

2.If no constructor was declared in a class, the compiler generates default constructor which has no parameter.

解答：（T）可能类不是亲生的吧。（PPT115页）

3.All methods in an abstract class must be declared as abstract methods.

解答：（F）没这个道理！道理在下面（PPT146页）：

4.If a base class declares an abstract method, a derived class must implement that method.

解答：（F）派生类确实要实现所有抽象方法，但是派生类也可以继续是抽象的呀！，这样就不用管实不实现了。

5.Sizeof can be applied to reference types.

解答：（F）

6.One file could have multiple namespaces.

解答：（T）PPT197页

7.Nested types can be interfaces and delegates.

解答：（T）PPT131页

8.If a method is marked as Protected, it will be able to access in the derived class.

解答：（T）

9.Sizeof can be applied to reference types.（重复了啊啊啊）

10.If a base declares an abstract method, a derived class should implement that method.（握草一个should一个must，搞什么鬼！）

三、填空

1．In C#, the type System.Int32 map to keyword _____int______

解答：这个还真没仔细看过，万一考个偏的怎么办。

2．In C#, if you want to change a thread’s state from suspended into running, what method you should call? Resume

3．The following class is often called _____Generic______

       class Buffer<Element> {

              private Element[] data;

              public Buffer( int size ) {…}

             public void Put(Element x) {…}

                public Element Get() {…}

4．Every interface member must be __implemented___ or ___inherited____ from a base class.

解答：接口的成员要么自己定义要么继承自父类。

接口不能包含常量、字段、操作符、构造函数、析构函数、任何静态成员、方法的实现；

5．??????

6．Write the output.

static void Main()
{
    String[] cities = {"London","Vienna","Paris","Linz", "Brussels"};
    //using Linq to Objects
    IEnumerable<string> result = from c in cities
    　　　　　　　　　　　　　　　　　where c.StartsWith("L")
    　　　　　　　　　　　　　　　　　orderby c
    select c.ToUpper();

    foreach (string s in result)
        Console.WriteLine(s);
    Console.ReadKey();
}

解答：原题目好像并不能输出什么啊，改了一下题目，他的意思应该是是要输出result内容。结果如下：

LINZ

LONDON

7． Fill in the blank

using System;

class Program
{
    static void Main()
    {
        Myclass m = new Myclass();
        int[] s = new int[5] { 1, 2, 3, 4, 5 };
        int smax, smin;
        m.MaxMin(s, out smax, out smin);

        Console.WriteLine("{0} {1}", smax, smin);
        Console.ReadKey();
    }
}
class Myclass
{
    public void MaxMin(int[] a, out int max, out int min)
    {
        max = min = a[0];
        for (int i = 1; i < a.Length; i++)
        {
            if (a[i] > max) max = a[i];
            if (a[i] < min) min = a[i];
        }
    }
}

解答：out的用法（默默在MaxMin前面加了一个public）。

8．Write the output.

delegate void Notifier (string sender);

void SayHello(string sender) 
{
    Console.WriteLine("Hello from " + sender);
}
void SayGoodBye(string sender) 
{
     Console.WriteLine("Goodbye from " + sender);
}

    Notifier greetings;
    greetings = SayHello;
    greetings += SayGoodBye;
    greetings("John");  
    greetings -= SayHello;
    greetings("John");

解答：代理的基本用法。输出结果：

Hello from John

Goodbye from John

9．Write the result of array A.

static void Main()
{
    int[] A = new int[5] { 1, 2, 3, 4, 5 };
    Object[] B = new Object[5] { 6, 7, 8, 9, 10 };

    Array.Copy(A, B, 2);

    foreach (int x in A)
        Console.WriteLine(x);

　　foreach (int x in B)
        Console.WriteLine(x);

　　Console.ReadKey();
}

解答：考察Copy的用法。这里面A没有变哦，反倒是B变成了{1,2,8,9,10}

输出结果（数组A内容）：

10.Please fill in the blanks.

namespace test
{
    public delegate void OnDBOperate();
    public class UserControlBase : System.Windows.Forms.UserControl
    {
        public event OnDBOperate OnNew;
        private void toolbar_ButtonClick(object sender, System.Windows.Forms.ToolBarButtonClickEventArgs e)
        {
            if (e.Button.Equals(BtnNew))
            {
                //Please write code to call OnNew events
                if (OnNew != null)
                    OnNew();
            }
        }
    }
}

四、简答

1.What is the difference between virtual method and the abstract method?

解答：抽象方法是只有定义、没有实际方法体的函数，它只能在抽象类中出现，并且在子类中必须重写；抽象方法是一种强制派生类覆盖的方法，必须被派生类覆写的方法，否则派生类将不能被实例化。抽象方法是可以看成是没有实现体的虚方法，如果类中包含抽象方法，那么类就必须定义为抽象类，不论是否还包含其它一般方法。

虚方法则有自己的函数体，已经提供了函数实现，而且允许在子类中重写或覆盖。虚方法可以不在派生类中重写。

2.C# uses different modifiers to confine the data security. There are 5 different modifiers. Please list out each of them and explain their security level.

解答：简单叙述了一下。

public 公有访问。不受任何限制。
private 私有访问。只限于本类成员访问，子类，实例都不能访问。
protected 保护访问。只限于本类和子类访问，实例不能访问。
internal 内部访问。只限于本项目内访问，其他不能访问。
protected internal 内部保护访问。只限于本项目或是子类访问，其他不能访问。