C # review lesson 1

1, Data type

1. Basic data type:
(1) Integer: byte short int long
(2) Floating point type: float double
(3) Boolean: bool
(4) Character type: cahr
2. Reference data type:
string array class interface

2, Constants and variables

1. Variables
(1) Variable definition: data type variable name;
(2) Variable assignment: variable name = value;
(3) Use of variables: first define, then assign, and then use
eag: int a=10;

2... Constant
(1) . constant definition: (const) data type constant name;
(2) . constant assignment: constant name = value;
(3) . use of constants: first define, then assign, and then use
eag:(const) int b=100;

3, Naming rules

Camel / hump naming method: the first letter of the word is lowercase, and the first letter of each other word is uppercase. It is mostly used to name variables: myStudent
Pascal: each word is capitalized, distinguished from lowercase, multi-user and named MiddleSchool for methods or classes

4, Type conversion

1. Display conversion (forced conversion): byte < – short (char) < – int < – long < – float < – double
Format: (force conversion of data type) variable name

/* int a = 10;
float b;
b = a;
//print(a+"\t"+b);//10  

Other conversion methods: int.Parse(); Convert.ToInt(); Convert.ToString();…

2. Implicit conversion (automatic type conversion): byte – > short (char) – > int – > long – > float – > double

class Program
    {
        static void Main(string[] args)
        {//Using Convert type conversion, you will succeed if you succeed, and throw an exception if you fail
           // int a = Convert.ToInt32("da5555");

            //If you succeed, you will succeed, and if you fail, you will throw exceptions
           // int b = int.Parse("dadad2121");

            //Try to convert a string to type int

            #region int.TryParse summary
            /*
         Summary:
             public static Int32 Parse(string s, NumberStyles style);
              Converts the string representation of a number to its 32-bit signed integer equivalent. A return value indicating whether the conversion was successful.
             
            Parameters:
           s:
             A string containing the number to convert


      When this method returns, if the conversion is successful, it contains a 32-bit unsigned integer value equivalent to the number contained in s; If the conversion fails, zero is included. If the s parameter is null or System.String.Empty, the format is incorrect, or the number represented is less than
          System.Int32.MinValue Or greater than System.Int32.MaxValue, the conversion fails. This parameter is passed without initialization; Initially in result
            Any value provided in is overwritten.

            s if true is successfully converted; Otherwise, it is false.
             */
            #endregion

            int number = 110;
           bool c= int.TryParse("123", out number);
            //If the conversion succeeds, enter number and return the value of c. if the conversion fails, return the value of number to 0 and return the value of c
            Console.WriteLine(c);
            Console.WriteLine(number);
            
        }
    }

5, Escape character

Escape character: a \ plus a special character to form a character with special meaning
\n: Line feed
\b: Backspace
\: backslash
\t: Tab
": double quotation marks

@Symbol:
1. Cancel the escape function of \ in the string
2. Keep the original format output

Use of plus sign:
1. Connection: when one side of the + sign is a string
2. Addition: both sides are numbers

6, Basic operation

1.+ - * / %
2. Relational operator: > > = < < = ==
3. Self increase and self decrease:
Whether it is before + + or after + +, the final result is to add 1 to this variable
In the expression: if it is the first + +, first add 1 to the variable itself, and then take the value after 1 to participate in the operation
If it is post + +, take the original value to participate in the operation. After the operation, add 1 to the variable itself
The deduction is the same as above

class Program
    {
        static void Main(string[] args)
        {//++The original value of number is added after, and then number is added by 1
         //++Add number+1 before, and then number+1

            int number = 10;
            // int result = 10 + ++number;// number 11  result 21
           /* number++;
            int result = 10 + number;*/
            

            int result = 10 + number++;// number 11  result 20
            /*int result=10+number;
             number++;
             
             */

            Console.WriteLine("number The values are:{0}´╝îresult The values are:{1}", number,result);


            int a = 5;
            int b = a++ + ++a * 2 + --a + a++;
            /* 5   6
             7*2   7 
            6     6
            6   7

            */

            Console.WriteLine("{0},{1}",b,a);

            
        }
    }

7, Logical operator

Logical and: & & true (1) false (0) multiplication
Logical or: | true (1) false (0) addition 1 + 1 = 1
Logical non:! 1 becomes 0 becomes 1

class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Xiao Su, please enter your Chinese score");
            int a = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Xiao Su, please enter your math score");
            int b = Convert.ToInt32(Console.ReadLine());

            bool c = a > 90 && b > 90;
            Console.WriteLine(c);

            //Judge leap year

            Console.WriteLine("Please enter the year to judge");
            int d = Convert.ToInt32(Console.ReadLine());
            //The year can be divided by 400 (2000)
            //Year can be divided by 4 but not 100 (2008)

            bool e = (d % 400 == 0) || (d % 4 == 0 && d % 100 != 0);//  Logic takes precedence over logic or

            Console.WriteLine(e);

        }
    }

8, VS common shortcut keys

Ctrl + s save
Ctrl + c copy
Ctrl + v paste
Ctrl + x cut
Ctrl + z undo
Ctrl + k +d quick alignment code
Ctrl + k + c quick comment selection
Ctrl + k + u to quickly de annotate the selected annotation content

9, Ternary operator

/// <summary>
/// 
///Expression 1? Expression 2: expression 3
///Expression 1 is generally a relational expression. Any formula using if else can use a relational expression
///Note: expression 2 and expression 3 must be consistent with the expression result type
///    bool a5 = false;
///   string s = a5 ? "Yes" : "No";
/// </summary>
class Program
    {    

        static void Main(string[] args)
        {

            Calculate the ratio of two numbers and find the maximum value
            //Console.WriteLine("please enter the first number:");
            //int a = Convert.ToInt32(Console.ReadLine());
            //Console.WriteLine("please enter the second number:");
            //int b = Convert.ToInt32(Console.ReadLine());
            //int c = a > b ? a : b;
            //Console.WriteLine(c);
            //if (a > b)
            //{
            //    Console.WriteLine(a);
            //}
            //else { Console.WriteLine(b); }

            ArrayList al = new ArrayList();
            al.Add("Zhang San");
            al.Add(1);
            al.Add('d');
            al.Add(true);
            //  al.Remove(1); / / delete a single element. Delete whoever writes it
            al.RemoveAt(2);//Delete elements according to Subscripts
            al.Insert(1, "Inserted");// Inserts an element before the specified location
            //al.Sort();
            al.Add("Big boy");
            if (!al.Contains("Big boy"))//Determines whether an element is in System.Collections.ArrayList  
            {
                al.Add("Big boy");
            }
            else
            {
                Console.WriteLine("Already");
            }
            foreach (object item in al)
            {
                Console.WriteLine(item);
            }




            List<string> list = new List<string>();
            list.Add("Zhang San");
            list.Add("Li Si");
            list.Add("Wang Wu");
            list.Add("Tian Liu");
            list.Add("Zhao Qi");

            for (int i = 0; i < list.Count; i++)
            {
                Console.WriteLine("for Cycle:" + list[i]);
            }

            list.RemoveAt(0);
            foreach (string item in list)
            {
                Console.WriteLine("foreach Iteration:" + item);
            }




        }
    }

Keywords: C#

Added by brailleschool on Sat, 09 Oct 2021 06:11:03 +0300