What is the use of static variable in C When to use it Why can t I declare the static variable inside method

Question

I have searched about static variables in C   but I am still not getting what its use is  Also  if I try to declare the variable inside the method it will not give me the permission to do this  Why   I have seen some examples about the static variables  I ve seen that we don t need to create an instance of the class to access the variable  but that is not enough to understand what its use is and when to use it   Second thing  class Book       public static int myInt   0     public class Exercise       static void Main                 Book book   new Book             Console WriteLine book myInt      Shows error  Why does it show me error                                            Can t I access the static variable                                            by making the instance of a class           Console ReadKey

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C  haven t static variables at all  You can declare static field in the particular type definition via C   Static field is a state  shared with all instances of particular type  Hence  the scope of the static field is entire type  That s why you can t declare static field within a method - method is a scope itself  and items declared in a method must be inaccessible over the method s border

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Static variables are used when only one copy of it is required  Let me explain this with an example   class circle       public float  PI  3 14F      public int Radius       public funtionArea int radius                return this radius   this  PI               class program       public static void main                 Circle c1   new Cirle            float area1   c1 functionRaduis 5           Circle c2   new Cirle            float area2   c1 functionRaduis 6             Now here we have created 2 instances for our class circle   i e 2 sets of copies of  PI  along with other variables are created  So say if we have lots of instances of this class multiple copies of  PI will be created occupying memory  So in such cases it is better to make such variables like  PI static and operate on them    class circle       static float  PI  3 14F      public int Radius       public funtionArea int radius                return this radius   Circle  PI               class program       public static void main                 Circle c1   new Cirle            float area1   c1 functionRaduis 5           Circle c2   new Cirle            float area2   c1 functionRaduis 6             Now no matter how many instances are made for the class circle   only one copy exists of variable  PI saving our memory

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The data members and function members that operate on the instance of the type are called instance members  The int   s ToString method  for example  are examples of instance members  By default  members are instance members   Data members and function members that don   t operate on the instance of the type  but rather on the type itself  must be marked as static  The Test Main and Console WriteLine methods are static methods  The Console class is actually a static class  which means all its members are static  You never actually create instances of a Console   one console is shared across the whole application

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Some  real world  examples for static variables   building a class where you can reach hardcoded values for your application  Similar to an enumeration  but with more flexibility on the datatype   public static class Enemies       public readonly static Guid Orc   new Guid   937C145C-D432-4DE2-A08D-6AC6E7F2732C         The widely known singleton  this allows to control to have exactly one instance of a class  This is very useful if you want access to it in your whole application  but not pass it to every class just to allow this class to use it   public sealed class TextureManager               private TextureManager              public string LoadTexture string aPath            private static TextureManager sInstance   new TextureManager             public static TextureManager Instance                       get   return sInstance                      and this is how you would call the texturemanager  TextureManager Instance LoadTexture  myImage png      About your last question  You are refering to compiler error CS0176  I tried to find more infor about that  but could only find what the msdn had to say about it      A static method  field  property  or event is callable on a class even   when no instance of the class has been created  If any instances of   the class are created  they cannot be used to access the static   member  Only one copy of static fields and events exists  and static   methods and properties can only access static fields and static   events

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You don t need to instantiate an object  because yau are going to use  a static variable  Console WriteLine Book myInt

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Static classes don t require you to create an object of that class instantiate them  you can prefix the C  keyword static in front of the class name  to make it static   Remember  we re not instantiating the Console class  String class  Array Class   class Book       public static int myInt   0     public class Exercise       static void Main                 Book book   new Book             Use the class name directly to call the property myInt           don t use the object to access the value of property myInt          Console WriteLine Book myInt            Console ReadKey

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Starting from this  Kartik Patel example    I have changed a little maybe now is more clear about static variable    public class Variable               public static string StaticName    Sophia            public string nonStName    Jenna            public void test                         StaticName   StaticName     Lauren                Console WriteLine    static   0   StaticName               nonStName   nonStName    Bean                Console WriteLine    NeStatic neSt  0    nonStName                        class Program               static void Main string   args                        Variable var   new Variable                var test                Variable var1   new Variable                var1 test                Variable var2   new Variable                var2 test                Console ReadKey                      Output    static  Sophia  Lauren   NeStatic neSt Jenna Bean   static  Sophia  Lauren Lauren   NeStatic neSt Jenna Bean   static  Sophia  Lauren Lauren Lauren   NeStatic neSt Jenna Bean    Class Variable  VS  Instance Variable in C    Static Class Members C   OR  Class Variable  class A          Class variable or   static member variable   are declared with        the  static   keyword      public static int i 20      public int j 10            Instance variable      public static string s1  static class variable     Class variable      public string s2  instance variable             instance variable    class Program       static void Main string   args                A obj1   new A                obj1 instance variables          Console WriteLine  obj1 instance variables             Console WriteLine A i           Console WriteLine obj1 j           Console WriteLine obj1 s2           Console WriteLine A s1            A obj2   new A                obj2 instance variables          Console WriteLine  obj2 instance variables             Console WriteLine A i           Console WriteLine obj2 j           Console WriteLine obj2 s2           Console WriteLine A s1            Console ReadKey                          https   en wikipedia org wiki Class variable   https   en wikipedia org wiki Instance variable  https   en wikipedia org wiki Static variable  https   javaconceptoftheday com class-variables-and-instance-variables-in-java  fbclid IwAR1 dtpHzg3bC5WlGQGdgewaTvuOI6cwVeFUtTV8IZuGTj1qH5PmKGwX0yM  https   docs microsoft com en-us dotnet csharp programming-guide classes-and-structs static-classes-and-static-class-members

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Static variable retains it s previous value until the program exit  Static is used by calling directly class Name Method   or class Name Property  No object reference is needed  The most popular use of static is C  s Math class  Math Sin    Math Cos    Math Sqrt

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A static variable shares the value of it among all instances of the class   Example without declaring it static   public class Variable       public int i   5      public void test                 i   i   5          Console WriteLine i             public class Exercise       static void Main                 Variable var   new Variable            var test            Variable var1   new Variable            var1 test            Console ReadKey              Explanation  If you look at the above example  I just declare the int variable  When I run this code the output will be 10 and 10  Its simple   Now let s look at the static variable here  I am declaring the variable as a static   Example with static variable   public class Variable       public static int i   5      public void test                 i   i   5          Console WriteLine i             public class Exercise       static void Main                 Variable var   new Variable            var test            Variable var1   new Variable            var1 test            Console ReadKey              Now when I run above code  the output will be 10 and 15  So the static variable value is shared among all instances of that class

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static variables are used when only one copy of the variable is required  so if you declare variable inside the method there is no use of such variable it s become local to function only    example of static is   class myclass       public static int a   0      Variables declared static are commonly shared across all instances of a class   Variables declared static are commonly shared across all instances of a class  When you create multiple instances of VariableTest class This variable permanent is shared across all of them  Thus  at any given point of time  there will be only one string value contained in the permanent variable   Since there is only one copy of the variable available for all instances  the code this permament will result in compilation errors  because it can be recalled that this variablename refers to the instance variable name  Thus  static variables are to be accessed directly  as indicated in the code

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In response to the  when to use it   question   I often use a static  class  variable to assign a unique instance ID to every instance of a class  I use the same code in every class  it is very simple     Instance ID ----------------------------------------        Class variable holding the last assigned IID     private static int xID   0         Lock to make threadsafe  can omit if single-threaded      private static object xIDLock   new object           Private class method to return the next unique IID          - accessible only to instances of the class     private static int NextIID                                     lock  xIDLock    return   xID                 Public class method to report the last IID used          i e  the number of instances created      public static int LastIID     return xID           Instance readonly property containing the unique instance ID     public readonly int IID   NextIID      -----------------------------------------------------   This illustrates a couple of points about static variables and methods    Static variables and methods are associated with the class  not any specific instance of the class  A static method can be called in the constructor of an instance - in this case  the static method NextIID is used to initialize the readonly property IID  which is the unique ID for this instance    I find this useful because I develop applications in which swarms of objects are used and it is good to be able to track how many have been created  and to track query individual instances   I also use class variables to track things like totals and averages of properties of the instances which can be reported in real time  I think the class is a good place to keep summary information about all the instances of the class

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On comparison with session variables  static variables will have same value for all users considering i am using an application that is deployed in server  If two users accessing the same page of an application then the static variable will hold the latest value and the same value will be supplied to both the users unlike session variables that is different for each user  So  if you want something common and same for all users including the values that are supposed to be used along the application code then only use static

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Try calling it directly with class name Book myInt

[c#] What is the use of static variable in C#? When to use it? Why can't I declare the static variable inside method?

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