variables, operators, expressions

variables, operators, Expressions

1. A statement is a command that can perform an operation. The simplest and most important C # syntax rule: You must use a semicolon to terminate all statements.

2.rules followed by identifiers:

▲ Use only letters, numbers, underscore characters

▲ identifiers must start with a letter or an underscore

3. Keywords and their meanings

Key words	Meaning
Abstract	Identifies a class or method that can be extended but not manifested and must be implemented.
As	A conversion operator that returns NULL if the conversion fails .
Base	Used to access a base class member that is hidden by a member of the same name in a derived class or construct.
bool	A simple type that represents a Boolean value.
Break	A jump statement that is used to exit from a loop or switch statement.
Byte	A simple type that represents an unsigned 8-bit length integer.
Case	Specifies a label in the switch statement. If the constant specified in the label matches the value of the switch expression, the statement associated with the tag is executed.
Catch	Defines a block of code that executes in-block code when a particular type of exception is thrown. Participate in try and finally.
Char	Represents A simple type of a Unicode character.
Checked	is both an operator and a statement. Ensures that the compiler and the runtime check for overflow when integer type operations or conversions occur.
Class	Indicates that a declaration is a declaration of a class type.
Const	Identifies a variable value that can be computed at compile time, that is, a value that cannot be modified once assigned.
Continue	The jump statement to return to the top of the loop.
Decimal	A simple type that represents a high-precision decimal number.
Default	In the switch statement, specify a set of statements that execute if there are no matching case clauses in front of them.
Delegate	Specifies that a declaration is a delegate type. A delegate encapsulates a method as a callable entity and can be called in a delegate entity.
Do	Specifies that a declaration is a delegate type. A delegate encapsulates a method as a callable entity and can be called in a delegate entity.
Double	A simple type that represents a single-digit double-precision floating-point value.
Else	if the condition is not true, then the statement after the else is executed if a part of the IF condition statement .
Enum	Represents a value type for a named constant cluster.
Event	A member that allows a class or object to provide notification, which must be a delegate type.
Explicit	An operator that defines the user-defined conversion operator, which is typically used to convert the built-in type to a user-defined type or to a reverse operation. An explicit conversion operator must be called at conversion time.
extern	Identifies a method that will be implemented externally (usually not in the C # language).
False	A Boolean literal.
Finally	Defines a block of code that executes after program control leaves the try code block. See try and catch keywords.
Fixed	When a block of code executes, a pointer is assigned to a variable at the fixed memory location.
Float	A simple type that represents a single-precision floating-point value.
For	Defines a looping statement that continues as long as the specified condition is satisfied.
Foreach	The elements (Arrays and collection objects) that are used to traverse a cluster.
Goto	A jump statement that redirects the program execution to a label statement.
If	A conditional statement that selects a statement execution based on the value of a Boolean expression.
Implicit	An operator that defines a user-defined conversion operator. Typically used to convert a predefined type to a user-defined type or to a reverse operation. The implicit conversion must be used at the time of conversion.
Inch	A part of the Foreach statement traversal syntax that is placed between the variable name and the cluster to traverse.
Int	Represents a simple type of a four-bit signed integer value.
Interface	Specifies a declaration as an interface type, that is, a contract that implements a class or construct that must be followed.
Internal	An access modifier. Internal code elements can only be accessed by other types within the same assembly. Assemblies can be DLLs or EXE files.
Is	Compares a comparison operator for two object types.
Lock	In a multithreaded program, set a mutex for the variable.
Long	A simple type that represents a four-bit signed integer value.
Namespace	Defines the type and namespace of a logical group.
New	The operator used to invoke the constructor. It is also a modifier used to hide and not overload an inherited method that has the same signature.
Null	Represents a literal value equivalent to 0 in a reference type .
Object	A predefined reference type that represents the ultimate base class for all reference types. is also an alias for the predefined type System.Object.
operator	Used to declare or load one operator.
Out	Identifies a parameter that is affected by a parameter value, but does not need to be initialized before passing in the method.
Override	A modifier that indicates that a method will override a virtual method or abstract method, or that an operator will override the same name operator defined in the base class.
Params	Declares an array of arguments. If used, the last parameter specified must be modified. Optional parameters are allowed.
Private	An access modifier. A private member can only be accessed within the type that defines the member.
Protected	An access modifier. A protected member can be accessed only in the type or derived type that defines the member.
Public	An access modifier. A public member can freely access inside and outside the class or namespace in which the member is defined.
ReadOnly	The value that identifies a variable cannot be modified after initialization.
Ref	Identifies a parameter that may be affected by a parameter value.
Return	A jump statement for jumping out of a method. Execution is returned to the method caller.
SByte	Represents a simple type of 8-bit signed integer.
Sealed	Prevents types from being derived, preventing methods and property from being overwritten.
Short	Represents a simple type with signed integer values.
sizeof	An operator that returns the length of a value type in bytes.
Stackalloc	Returns a pointer to a block of memory allocated on the heap.
Static	A static member is associated with the type in which it is declared, not the entity of the type.
String	A predefined reference type that represents a Unicode string. is an alias for the System.String predefined type.
struct	A Struct is a value type that can declare constants, fields, methods,property, indexers, operators, constructors, and inline types.
Switch	A selection statement that performs a list of statements associated with the expression matching label.
This	Refers to the current entity of a type.
Throw	Causes an exception to be thrown.
True	A Boolean literal.
Try	One of the components of the exception handling code block. Try the code block includes code that might throw an exception. See catch and finally keywords.
typeof	An operator that returns the type of the passed-in parameter.
UInt	A simple type that represents a four-bit unsigned integer value.
ULong	A simple type that represents a four-bit unsigned integer value.
Unchecked	Prevent overflow checking.
Unsafe	Labels the code block, method, or class that contains the pointer action.
UShort	Represents a simple type of a non-signed integer value.
Using	When used with namespaces, theusing keyword allows access to the type in that namespace without specifying its full name. Also used to define The scope of the finalization operation.
Virtual	A method modifier that identifies a method that can be covered by a vent.
void	The return type of the no return value method.
Volatile	Identifies a attributethat can be modified by the operating system, certain hardware devices, or concurrent threads.
While	The while condition statement executes one or more 0 or more times depending on the condition. The while part of the DO statement specifies the loop abort condition.

4. Named variables

▲ The name does not begin with an underscore

▲ do not create identifiers that are only case-sensitive, because in applications developed in other languages, it is not good to reuse classes, perhaps those languages are case-insensitive

▲ name starts with lowercase letters

▲ in identifiers that contain multiple words, start with the second word and capitalize the first letter

5, C # does not allow the use of unassigned variables.

6. Solution files using the. sln suffix as the extension, a solution can contain multiple projects. The project file uses the. csproj extension.

7, if the expression 0.0/0.0, the result is Nan (not a number), if the calculation 10+nan, the result is Nan, if the calculation infinity (infinity) +10, the result is infinity, but infinity*0, the result is 0,nan* 0 The result is Nan. The modulo operator applies to all numeric types, and the result is not necessarily an integer.

variables, operators, expressions