CTRL+K CTRL+C; (I don’t know what the designer thought, stupid)
VS uncomment: CTRL+K CTRL+U; (stupid dead)
CTRL+A CTRL+K CTRL+F; (stupid dead)
PS: Finally couldn’t bear to change VS Code 😂😂😂😂😂
1. If statements
if(Condition 1) {execute 1; }else if(Condition 2) {execute 2; }else{other execution; }Copy the code
If the execution statement has only one sentence, you can also abbreviate it:
if(Condition 1) Perform 1 (only one sentence);else if(Condition 2) Perform 2 (only one sentence);else(Condition 3) other execution;Copy the code
2. A switch statement
switch (op) {
case "+":
op = "a+b";
break;
case "-":
op = "a-b";
break;
case "*":
case "×":
op = "a*b";
break;
default:
op = "";
break;
}Copy the code
The switch variable can be an integer string Boolean char enumeration or a type that can be null, but nothing else
Case can only judge a fixed value;
Each case must break, including default;
Multiple cases executing the same statement can be abbreviated;
3. While statement
while (true) {
break; //continue;return;breakAdd equal jump statement; };Copy the code
4. The for loop
for(int i = 0; i < 10; I++) {execute statement; }Copy the code
4.1 Foreach Traversal function
foreach (int i in arr){
}Copy the code
4.2 Some methods of string
string str = "My name is Annie.";
Console.WriteLine(str.IndexOf("Ann"));
str.StartsWith("我"); // Determine the leading character, return Boolean; string[] arr; arr = str.Split("Call"); // Returns a string group with a character cut string; str = str.Insert(2,"Small"); // Insert the character before the second; Console.WriteLine(str); str = str.Replace("Small"."Big"); // Replace old characters with new characters; Console.WriteLine(str); str = str.Remove(2, 1); // Remove a console. WriteLine(STR) from the second; str = str.Remove(2); // Remove the Console.WriteLine(STR) from the second;Copy the code
5. Method (function) structure
Private static return value method name (parameter) {
Logical statement;
Return Return value; Return (void); return (void); return (void);
}
private static int getWeekByDay(int year, int month, int day)
{
DateTime dt = new DateTime(year, month, day);
return (int)dt.DayOfWeek;
}Copy the code
6. Overloading methods (functions)
Methods with the same name, return the same value, but with different parameters are treated as different methods, and can be overloaded by passing in different parameters when called
Example:
private static long CountSec(int min) {
return min * 60;
}
private static long CountSec(int hour,int min)
{
return hour*CountSec(60)+min * 60;
}
private static long CountSec(int day,int hour, int min)
{
returnDay * CountSec(24,0) + hour * CountSec(60) + min * 60; }Copy the code
7. Recursion
Recursion advantage: logic simplification
Disadvantages of recursion: Beware of stack overflow, poor performance
Example: Recursive factorial: 5*4*3*2*1
s3*2*1tatic void Main(string[] args)
{
Console.WriteLine (DiGui(5));
}
private static int DiGui(int num) {
if (num == 1) return 1;
return num * DiGui(num - 1);
}Copy the code
An array of 8.
Arrays must be of the same data type
Arrays are written as follows:
① Declaration, initialization, assignment
int[] a; // Declare array a = new int[3]; // Initialize array a[2] = 2; // Array assignmentCopy the code
② Initialization plus assignment
Int [] arr = new int[5] {1,2,3,4,5};Copy the code
③ Declaration + initialization + assignment
Int [] arr = {1,2,3,4,5};Copy the code
④ Anonymous array
,53,64,77,88 GetMax (new int [] {12})Copy the code
9. Var inferred types
Infer the type from the assigned data
10. Declare the superclass type assignment subclass object
Example: Declare the parent class, pass the parameter pass any subclass can be.
Private static void fun1(Array arr) {execute statement; }Copy the code
Random number 11.
static Random random = new Random(); // This sentence is written outside the method, inside the class.
random.Next(1, 34); // include the head but not the tail;
12. Array methods
① Get the array length
An array of Length
② Clear elements
Attention!! Clear is not delete. Clear simply clears the value to the default !!!!
Array.Clear(Array, start position, Clear length);
Example: array. Clear(arr, 2, 4);
③ Array copy elements
(1) array. Copy(source Array, source Array start index, target Array, target Array start index, Copy length);
int[] arr = { 1, 4, 2, 6, 7, 9 }; int[] arr2 = { 0, 0, 0, 0, 0, 0 }; Array. Copy (arr2 arr, 2, 2, 3);Copy the code
(2) array. Copy(source Array, destination Array,, Copy length); // Assign copies from the first one
Copy the source array into the target array starting at index
Source array.CopyTo(target array, start index of target array);
Arr. CopyTo (arr2, 0);
⑤ Array cloning
arr2=(int[])arr.Clone(); // Because Clone returns Object;
⑥ Find elements
Array.indexof (Array, element) // Returns the element index if there is no such element, returns -1;
Array.IndexOf (arr,6)
Array.LastIndexOf (arr,2)
⑦ Array sort
Array.Sort (arr); // No return value
Array inversion
Array.Reverse (arr);
13. Two-dimensional arrays
Int [and] a = new int [5, 3];
Can also:
Int [,] arr={{1,2,3}, {4,5,6}};
① A two-dimensional array can also be traversed
foreach(int each in arr){
Console.WriteLine (each);
}Copy the code
② Get the number of rows and columns in the array
Console.WriteLine(arr.GetLength(0)); / / lines of the Console. WriteLine (arr. GetLength (1)); / / the number of columnsCopy the code
14. Staggered arrays
int[][] arr; arr=new int[4][]; Arr [0] = new int [] {1, 2, 3}; Arr [1] = new int [] {4, 5}; arr[2]=new int[]{6}; Arr [3] = new int [] {7,8,9,10}; Arr [4] = new int [] 11, 12} {;Copy the code
Each element of a jagged array is an array
(2) Interleaved arrays can also be foreach traversal // double traversal;
int[][] arr; arr=new int[4][]; Arr [0] = new int [] {1, 2, 3}; Arr [1] = new int [] {4, 5}; arr[2]=new int[]{6}; Arr [3] = new int [] {7,8,9,10}; arr[0][0]=6; foreach(int[] eachArrin arr){
foreach(int each in eachArr){
Console.Write(each+"\t");
}
Console.WriteLine();
}Copy the code
Attention!!!!!! Each element of a jagged array is an array so the for loop should
for (int i = 0; i < arr.Length; i++)
{
for (int j = 0; j < arr[i].Length; j++)
{
Console.Write(arr[i][j] + "\t");
}
Console.WriteLine();
}Copy the code
15. Parameter array
When the type of arguments is certain but the number is uncertain, an array is appropriate
Parameter array:
private static int Sum(params int[] arr){}
When sending parameters, you can:
sum();
The Sum (new int [] {1, 2, 3});
The Sum (1, 2, 3);
Summary of parameter array features:
① Inside the method, the argument array is just an ordinary array.
2. Pass array. Pass variable count. 3