Day7

一、Looping

1、for 循环

for (int i = 0; i < 5; i++)
{
 Console.WriteLine(i);
}
//输出：
//0
//1
//2
//3
//4

2、do-while循环

int[] numbers = new int[] { 6, 7, 8, 10 };
int sum = 0;
int i = 0;
do
{
 sum += numbers[i];
 i++;
} while (sum <= 10 && i < numbers.Length);
 
System.Console.WriteLine(sum); //输出  13

3、Foreach 循环

var list = new List<string>();
list.Add("Ion");
list.Add("Andrei");
foreach(var name in list)
{
 Console.WriteLine("Hello " + name);
}

//相当于
var list = new List<string>();
list.Add("Ion");
list.Add("Andrei");
IEnumerator enumerator;
try
{
 enumerator = list.GetEnumerator();
 while(enumerator.MoveNext())
 {
 string name = (string)enumerator.Current;
 Console.WriteLine("Hello " + name);
 }
}
finally
{
 if (enumerator != null)
 enumerator.Dispose();
}

4、循环样式

While

while(条件)
{
 
}

Do

do
{
 
} while(条件)

For

for ( int i = 0; i < array.Count; i++ )
{
 var currentItem = array[i];
}

Foreach

foreach ( var item in someList )
{
}

Foreach Method

list.ForEach(item => item.DoSomething());
//或者
list.ForEach(item => DoSomething(item));
// 或使用一个方法组
list.ForEach(Console.WriteLine);
// 使用一个数组
Array.ForEach(myArray, Console.WriteLine);

5、嵌套循环

双层for

for (int i = 1; i <= 5; i++)
{
 for (int j = 1; j <= 5; j++)
 {
 int product = i * j;
 Console.WriteLine("{0} times {1} is {2}", i, j, product);
 }
}

6、continue

结束当前循环

for (int i = 1; i <= 10; i++)
{
 if (i < 9)
 continue;
 Console.WriteLine(i);
}
//结果是9（换行）10

7、while循环

int n = 0;
while (n < 5)
{
 Console.WriteLine(n);
 n++;
}
/*结果
0
1
2
3
4
*/

8、break

结束本次循环。

六、指类型与参考类型

1、 Passing by reference using ref keyword——使用ref关键字通过引用传递

 

 2、Changing values elsewhere

  class Program
    {
        public static void Main()
        {
            var studentList = new List<Student>();
            studentList.Add(new Student("Scott", "Nuke"));
            studentList.Add(new Student("Vincent", "King"));
            studentList.Add(new Student("Craig", "Bertt"));
            studentList[0].FirstName = "Duke";
            studentList[1].LastName = "Kong";
            studentList[2].LastName = "Brett";
            PrintPrintingList(studentList);

            Console.ReadKey();
        }
        private static void PrintPrintingList(List<Student> students)
        {
            foreach (Student student in students)
            {
                Console.WriteLine(string.Format("{0} {1}", student.FirstName, student.LastName));
            }
        }
    }
    public class Student
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public Student(string firstName, string lastName)
        {
            this.FirstName = firstName;
            this.LastName = lastName;
        }
    }

 结果：

 3、Assignment

分配给List<int>的变量不会创建List<int>的副本。相反，它将引用复制到List<int>。我们调用以这种方式的类型引用类型。

var a = new List<int>();
var b = a;
a.Add(5);
Console.WriteLine(a.Count); // 结果： 1
Console.WriteLine(b.Count); // 结果： 1

 4、 Passing by reference——通过引用值传递

public static void Main(string[] args)
{
 ...
 DoubleNumber(ref number); 
 Console.WriteLine(number); // 输出8
 ...
}
public void DoubleNumber(ref int number)
{
 number += number;
}

七、Built-in Types——内置类型

1、Conversion of boxed value types——盒装值类型的转换（像强制转换）

 2、Comparisons with boxed value types

3、Immutable reference type - string——不可变的引用类型-字符串

 以下三种，s的输出都是hello.

// assign string from a string literal
string s = "hello";
// assign string from an array of characters
char[] chars = new char[] { 'h', 'e', 'l', 'l', 'o' };
string s = new string(chars, 0, chars.Length);
// assign string from a char pointer, derived from a string
string s;
unsafe
{
 fixed (char* charPointer = "hello")
 {
 s = new string(charPointer);
 }
}

此处string 是重写的，以下是里面参数。第二个startIndex,字符开始的地方，同样的，第几个开始，后面对应的字符的长度就要对应的减去。

 八、Aliases of built-in types

 1、Built-In Types Table——内置类型表

 常用的：

//C# Type .NET Framework Type
bool System.Boolean
byte System.Byte
sbyte System.SByte
char System.Char
decimal System.Decimal
double System.Double
float System.Single
int System.Int32
uint System.UInt32
long System.Int64
ulong System.UInt64
object System.Object
short System.Int16
ushort System.UInt16
string System.String

int number = 123;
System.Int32 number = 123;

int和Syetem.Int32之间可以相互替换

九、Anonymous types——匿名类型

1、Creating an anonymous type

string foo = "some string";
var anon3 = new { foo.Length };
// anon3.Length == 11
var anon4 = new { foo.Length <= 10 ? "short string" : "long string" };
// compiler error - Invalid anonymous type member declarator.
var anon5 = new { Description = foo.Length <= 10 ? "short string" : "long string" };
// OK

 2、Anonymous type equalit

 

注意：当且仅当两种匿名类型的属性具有相同的名称和类型，且以相同的顺序出现时，才认为这两种匿名类型是相同的。

3、Generic methods with anonymous types

 泛型方法允许通过类型推理来使用匿名类型。这意味着LINQ表达式可以与匿名类型一起使用：

var products = new[] {
 new { Amount = 10, Id = 0 },
 new { Amount = 20, Id = 1 },
 new { Amount = 15, Id = 2 }
};
var idsByAmount = products.OrderBy(x => x.Amount).Select(x => x.Id);
// 这里idsByAmount: 0, 2, 1

4、Instantiating generic types with anonymous types ——使用匿名类型实例化泛型类型（见泛型&匿名中的例子）

var anon = new { Foo = 1, Bar = 2 };
var anon2 = new { Foo = 5, Bar = 10 };
List<T> CreateList<T>(params T[] items) {
 return new List<T>(items);
}
var list1 = CreateList(anon, anon2);

5、Implicitly typed arrays ——隐式类型的数组

var arr = new[] {
 new { Id = 0 },
 new { Id = 1 }
};