C# Section 3 (Operators)

An operator is a symbol that tells the compiler to perform a specific mathematical or logical operation. C# has a wealth of built-in operators, classified as follows:

1. arithmetic operators
2. relational operator
3. Logical Operators
4. bitwise operators
5. assignment operator
6. Other Operators
   Arithmetic
   Operators The following table shows the arithmetic operators supported by C#. Assuming that the value of variable A is 10 and the value of variable B is 20, then:
   
   Note: ++a is to perform an auto-increment operation on the value of a first, Then assign it to a variable;
   relational operators
   The following table shows all the relational operators supported by C#, assuming that the value of variable A is 10 and the value of variable B is 20, then:
   
   Logical operators
   The following table shows all the logical operators supported by C# operator, assuming that variable A is true and variable B is boolean false, then:
   
   Bitwise operators
   Bitwise operators act on bits and perform operations bit by bit. The truth table for &, |, and ^ is as follows:
   
   If A equals 60, and B=13, now in binary format, they look like this:

A=0011 1100
B=0000 1101
-------------------
A&B=0000 1100   //与运算，11为1，其余为0
A|B=0011 1101   //或运算，00为0，其余为1
A^B=0011 0001   //异或运算，相同为0，不同为1
~A=1100 0011   //取反

The following table lists the bit operators supported by C#. Assuming that the value of variable A is 60 and the value of variable B is 13, then:

Assignment operator

Other operators
The following table lists some other important operators supported by C#, Including sizeof, typeof, and ? :.

Operator precedence in C#

Note:
The results of &, | are exactly the same as &&, ||, but && and || have better performance. Because && and || both check the value of the first operand, if the result can already be judged, the second operand is not processed at all

C# judgment##

1. If-else combination

            if（"条件表达式"）
                {

            }else if("条件表达式"){

            }
            else
            {

            }

2、switch

demo:

static void Main(string[] args)
        {
            Console.WriteLine("请输入您的成绩等级：");
            char grade =Convert.ToChar(Console.ReadLine());
            switch(grade)//switch后面的表达式必须为整型或者枚举类型，或是一个class类型，其中class有一个单一的转换函数将其转换为整形或枚举类型
            {
                case 'A'://case后面的表达式必须与switch中的变量具有相同的数据类型，且必须为常量
                    Console.WriteLine("you are so great！");
                    break;
                case 'B':
                case 'C':
                    Console.WriteLine("do well");
                    break;
                case 'D'://在下一个case语句之前必须有break
                    Console.WriteLine("try again");
                    break;
                default:
                    Console.WriteLine("this gread is invalid");
                    break;
            }
            Console.WriteLine("您的成绩为：{0}", grade);
            Console.ReadKey();
}

3. Nested switch

static void Main(string[] args)
        {
            Console.WriteLine("select a integer from 100,200：");
            int a =Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("select another integer from 100,200：");
            int b= Convert.ToInt32(Console.ReadLine());
            switch(a)
            {
                case 100:
                    Console.WriteLine("第一个输入的值为100进入第二关");
                        switch(b)
                    {
                        case 100:
                            Console.WriteLine("第二关输入的值仍为100");
                            break;
                        case 200:
                            Console.WriteLine("第二关输入的值为200");
                            break;
                        default:
                            Console.WriteLine("第二关输入不正确，挑战失败");
                            break;
                    }
                    break;
                default:
                    Console.WriteLine("第一关挑战失败，无法继续游戏");
                    break;
            }
            Console.WriteLine("第一次输入的值为：" + a+ ",第二次输入的值为：" + b);
            Console.ReadKey();
}

Conditional operator? :

C# loop

1. While loop: If the condition is false, it will jump out of the loop theme and execute the next sentence immediately following the while loop.
2. For and foreach

demo:

static void Main(string[] args)
        {
            int[] inbarry = new int[] {11,4,5,9,66,8,59,78,5 };
            foreach(int i in inbarry)
            {
                Console.WriteLine("使用foreach遍历结果："+i);
            }
            Console.WriteLine();
            for(int i=0;i<inbarry.Length;i++)
            {
                Console.WriteLine("使用for遍历结果：" + inbarry[i]);
            }
            Console.WriteLine();

            //设置集合中元素的计算器
            int count = 0;
            foreach(int i in inbarry)
            {
                Console.WriteLine("Element #{0}:{1}", count, i);
                count++;
            }
            Console.WriteLine("Number of elements in the array:{0}", count);
 }            

do-While loop
do-While is guaranteed to be executed at least once

static void Main(string[] args)
        {
            int a = 66;
            do
            {
                Console.WriteLine("do while里面的a的值：{0}", a);
                a++;
            } while (a < 67);//注意此处有分号



            while(a<67)//此时的a已经变为了67所以已不再成立
            {
                Console.WriteLine("while里面的a的值：{0}", a);
                a++;
            }
            Console.ReadKey();
        }

Loop nesting
eg: Use loop nesting to find prime numbers from 2 to 100