Preface
This article is an introduction to C#. It is a summary based on a certain knowledge of C language or C++. Therefore, many basic knowledge of C language will be omitted. However, some knowledge unique to C# or relatively rare or important in C language will also be summarized. In the blog post.
Table of contents
a. Conversion between same types
b. Conversion between different large types
a. Parentheses forced transfer
b.Parse method forcefully converts the string type into the corresponding type
d. Convert other types to string
1.string can be concatenated using +
1. Between different numerical types
2. Special type char string bool
2. Logical operator short-circuit rules
4. Bit inversion~ (Just understand it)
5. Move left<< and move right>> (just understand it)
1. Input and output
- Console.WriteLine() prints a line of information and automatically wraps the line
- Console.Write() will not automatically wrap the line after printing the information.
- Console.ReadLine() user input, click Enter to end
- Console.ReadKey() will end when the user presses the keyboard any time
2. Variables
1. Fold the code
Function: Folds the code wrapped in the middle to avoid messy code editing.
#region MyRegion
...
#endregion2. Declare variables
Formula: variable type variable name = initial value;
There are 14 types of variables:
a.Signed integer variable
Can store positive and negative numbers and 0. The approximate range is given below (an error will be reported if the value exceeds the range when assigning)
- sbyte -128~-127
- int -2.1 billion~2.1 billion
- short -32768~32767
- long -9 trillion ~ 9 trillion
Sample code
sbyte a = 1;
Console.WriteLine("存储的数："+a); //输出之间的连接用+b. Unsigned integer variable
Can store a certain range of 0 and positive numbers
- byte 0~255
- uint 0~4.2 billion
- ushort 0~65535
- ulong 0~18 trillion
c.Floating point number
- float stores 7 or 8 significant digits, depending on compiler rounding starting with non-zero digits from left to right.
- Double stores 15~17 significant digits. The default double type for declaring decimals in C# is
- decimal stores 27~28 bits
float f = 0.1234f; //后面要加f 大小写均可
double d = 0.12456434;
decimal de = 0.124543534234t254m; //后面要加m 大小写均可d.Special type
- bool variable value is true or false, indicating true or false data type
- char stores a single character and encloses the value to be assigned in single quotes.
- string stores the string in double quotes to enclose the value to be assigned.
string s1="hello", s2="world", s3="good"; //多个变量同时声明3. Constants
Declaration of constants (characteristics: must be initialized and cannot be modified)
const variable type variable name = initial value;
const int i = 10;4. Escape characters
Formula: \character
Commonly used escape characters are as follows:
| apostrophe |
\' |
| Double quotes |
\" |
| newline |
\n |
| slash |
\\ |
| Tab tabulation | \t |
| backspace | \b |
5. Type conversion
1. Implicit conversion
Rules: (automatic conversion between different types) large range to small range
a. Conversion between same types
long a = 1;
int b = 2;
a = b;//int隐式转换为long
b = a;//这句是不对的！小范围不能转大范围For floating point numbers, it should be noted that the decimal type cannot use implicit conversion to store double and float, but float can be converted to double. There is no implicit conversion between special types bool, char and string.
b. Conversion between different large types
! Signed variables cannot be implicitly converted to unsigned variables
Error code example:
ushort us2 = 1;
sbyte sb2 = 1;
us2 = sb2;//错误代码！不能转换! Unsigned variables can be converted to signed variables, but the prerequisite is that the scope covered by the signed variable must include the unsigned type.
int i2 = 1;
uint ui2 = 1;
byte b2 = 1;
i2 = ui2;// 错误！无法覆盖无符号数的全部范围
i2 = b2;// 正确代码- Floating point numbers can load any type of integer, whether unsigned or signed (decimal cannot implicitly store float and double but can implicitly store integers)
- Integers cannot implicitly store floating point numbers
- The bool type cannot be implicitly converted to other types.
- Char cannot implicitly store variables of other types, but the char type can be converted to the int type, and the int type can be implicitly converted to other types.
2.Explicit conversion
Requires manual handling of casts
Formula: variable type variable name = (variable type) variable
a. Parentheses forced transfer
(1) Between the same categories (unsigned integers, signed integers, floating point numbers), forced conversion of brackets may cause range problems and cause exceptions.
short s = 1;
int i = 1;
s = (short)i;(2) Between different types
- Forced conversion between signed and unsigned can also occur, but range issues may occur.
- Converting floating point numbers to integers is mainly a matter of accuracy
- Bool and string do not support forced transfer.
b.Parse method forcefully converts the string type into the corresponding type
Variable type.Parse("string") The string must be able to be converted into the corresponding type, otherwise an error will be reported
int i4 = int.Parse("123");
float f3 = float.Parse("1.232");
bool b = bool.Parse("true");
int i4 = int.Parse("123.45");//错误语句，会报错！
short s4 = short.parse("300000");//错误语句，超出范围，会报错！c.Convert method
More accurate conversion between types
Convert.To target type (variable or constant) Converting a string to the corresponding type must be legal and compliant
int a = Convert.ToInt32("12");
int a = Convert.ToInt32(12.2f);//正确语句 且Convert精度更高，可以四舍五入
int a = Convert.ToInt32(ture);//正确语句 true转为1，false转为0
int a = Convert.ToInt32('a');//正确语句 char转为对应ASCII码
int a = Convert.ToInt32("12.2");//错误，不合法转换- Convert other methods ToSByte(), ToInt16(), ToInt64() //16 represents short, 32 represents int, 64 represents long
- Similarly, if it is an unsigned type ToByte(), ToUInt16/32/64()
- Floating point numbers: ToSingle(), ToDouble(), ToDecimal()
- Special types: ToBoolean(), ToChar(), ToString()
d. Convert other types to string
The function is to splice and print
Variable.ToString(); //Any type can be used
string str = 1.ToString();
Console.WriteLine("123"+1+true);//这句话是正确的，后面两个会默认调用ToString方法6. Exception catching
Use exception capture to prevent the program from getting stuck when the code reports an error.
Basic syntax:
try
{
//希望进行异常捕获的代码块
//如果出错执行catch中的
}
catch
{
//catch(Excepetion e) 具体报错跟踪 通过e得到具体错误信息
}
//可选部分
finally
{
//不管有没有错都会执行
}7. Arithmetic operators
No different from C language
8. String splicing
1.string can be concatenated using +
string str = "123";
str = str + "456";//正确
str = str + 1;//正确，默认调用1.ToString();
str += "1" + 4 + true;//正确，复合运算和ToString()都起作用2. String splicing method 2
string.Format("Content to be spliced", content 1, content 2);
The content that you want to splice is replaced with {number} with placeholders: 0~n in order.
string str2;
str2 = string.Format("我是{0}，我今年{1}岁，我想要{2}","Daniel",18,"study");3.Console printing splicing
If the following content is more than the placeholder, no error will be reported, but if it is less than the placeholder, an error will be reported.
Console.WriteLine("A{0},B{1},C{2}",1,ture,false);9. Conditional operator
Notation is the same as C language
1. Between different numerical types
Rule: Feel free to do conditional operator comparisons
int i = 5;
float f = 1.2f
short s = 2;
byte by = 20;
uint ui = 222;
// 以下语句都成立 只要是数值都可以进行比较
result = i > f;
result = f < d;
result = f > by;2. Special type char string bool
Rule: == and != can only be compared between the same type
Since char is a special integer type, it can be compared with its own type, compared with numeric types, and compared with character types.
char c = 'a';
result = c > 123;
result = c > 'B';10. Logical operators
Logical AND: && Logical OR: || Logical NOT: !
Notations and rules are the same as in C language
1. Attention
Among logical operators, logical NOT (!) has the highest priority, and logical AND (&&) has higher priority than logical OR (||).
Logical operators have lower precedence than conditional operators and arithmetic operators
2. Logical operator short-circuit rules
As long as the left side of logical AND or logical OR satisfies the condition, the right side does not need to be executed again.
For example, if logical AND is false, then the expression on the left is false, and the right side does not need to be executed again.
11. Bit operators
Rule: Concatenate two values to perform bit calculations and convert the values to binary
1. Bitwise AND operation &
Rule: If there is 0, then 0
int a = 1; // 002
int b = 5; // 101
int c = a & b;
// 001 & 101 = 001 所以c也就是12. Bitwise OR operation|
There is 1 or 1
1|0=1
3.XOR operation ^
Rule: Same as 0, different as 1
- 1 ^ 1 = 1
- 0 ^ 0 = 1
4. Bit inversion~ (Just understand it)
Write in front of the value to convert the value to binary
0 changes to 1, 1 changes to 0, involving complement code
5. Move left<< and move right>> (just understand it)
Let the binary system of a number be shifted left and right
Shift a few bits to the left and add a few 0s to the right.
Move a few numbers to the right and remove a few numbers to the right.
12. Ternary operator
The principle is equivalent to C language
13. if statement
The principle is equivalent to C language
14. switch statement
The principle is equivalent to C language
15. while statement
The principle is equivalent to C language
16. do while statement
The principle is equivalent to C language
17. for loop
The principle is equivalent to C language
The next article is a summary of the basic knowledge of C#, welcome to continue reading
Summary of basic knowledge of C# (based on C language)_Daniel's blog-CSDN blog