C Creating and using Functions

Question

I need help with C  programming  I am new to it and I come from C background   I have a Console Application like this   using System  using System Collections Generic  using System Linq  using System Text   namespace Add Function      class Program            static void Main string   args                   int a           int b           int c            Console WriteLine  Enter value of  a               a   Convert ToInt32 Console ReadLine               Console WriteLine  Enter value of  b               b   Convert ToInt32 Console ReadLine                 why can t I not use it this way           c   Add a  b            Console WriteLine  a   b    0    c            END   Main        public int Add int x  int y                    int result   x   y           return result           END   Add       END      Program    END         Add Function   It gives me this error on the line that I call Add        An object reference is required for the non-static field  method  or property  Add Function Program Add int  int     Can anyone please explain to me why I have this problem   Is this because the architecture of C  is different than C  and the way I call it is wrong   Thanks

User · Answer

This code gives you an error because your Add function needs to be static:

static public int Add(int x, int y)

In C# there is a distinction between functions that operate on instances (non-static) and functions that do not operate on instances (static). Instance functions can call other instance functions and static functions because they have an implicit reference to the instance. In contrast, static functions can call only static functions, or else they must explicitly provide an instance on which to call a non-static function.

Since public static void Main(string[] args) is static, all functions that it calls need to be static as well.

User · Answer

You should either make your Add function static like so   static public int Add int x  int y         int result   x   y      return result       END   Add   static means that the function is not class instance dependent   So you can call it without needing to create a class instance of Program class   or you should create in instance of your Program class  and then call Add on this instance   Like so   Program prog   new Program    prog Add 5 10

User · Answer

The reason why you have the error is because your add function is defined after your using it in main if you were to create a function prototype before main up above it with public int Add int x  int y   or you could just copy and paste your entire Add function above main cause main is where the compiler starts execution so doesn t it make sense to declare and define a function before you use it hope that helps   D

User · Answer

What that build error is telling you  that you have to either have an instance of Program or make Add static

User · Answer

Note  in C  the term  function  is often replaced by the term  method   For the sake of this question there is no difference  so I ll just use the term  function     Thats not true  you may read about  func type  Lambda expressions    anonymous function using delegates type    action type  Lambda expressions    Predicate type Lambda expressions   etc   etc    this will work   using System  using System Collections Generic  using System Linq  using System Text  using System Threading Tasks   namespace ConsoleApplication1       class Program               static void Main string   args                        int a             int b             int c              Console WriteLine  Enter value of  a                 a   Convert ToInt32 Console ReadLine                 Console WriteLine  Enter value of  b                 b   Convert ToInt32 Console ReadLine                 Func lt int  int  int gt  funcAdd    x  y    gt  x   y             c funcAdd Invoke a  b              Console WriteLine Convert ToString c

User · Answer

static void Main string   args                Console WriteLine  geef een leeftijd            int a   Convert ToInt32 Console ReadLine              Console WriteLine  geef een leeftijd            int b   Convert ToInt32 Console ReadLine              int einde   Sum a  b           Console WriteLine einde             static int Sum int x  int y                int result   x   y          return result

User · Answer

Just make your Add function static by adding the static keyword like this   public static int Add int x  int y

User · Answer

static void Main string   args                Console WriteLine  geef een leeftijd            int a   Convert ToInt32 Console ReadLine              Console WriteLine  geef een leeftijd            int b   Convert ToInt32 Console ReadLine              int einde   Sum a  b           Console WriteLine einde             static int Sum int x  int y                int result   x   y          return result

User · Answer

Because your function is an instance or non-static function you should create an object first   Program p new Program    p Add 1 1

User · Answer

Note  in C  the term  function  is often replaced by the term  method   For the sake of this question there is no difference  so I ll just use the term  function    The other answers have already given you a quick way to fix your problem  just make Add a static function   but I d like to explain why   C  has a fundamentally different design paradigm than C  That paradigm is called object-oriented programming  OOP   Explaining all the differences between OOP and functional programming is beyond the scope of this question  but here s the short version as it applies to you   Writing your program in C  you would have created a function that adds two numbers  and that function would exist independently and be callable from anywhere  In C  most functions don t exist independently  instead  they exist in the context of an object  In your example code  only an instance  an object  of the class Program knows how to perform Add  Said another way  you have to create an instance of Program  and then ask Program to perform an Add for you   The solutions that people gave you  using the static keyword  route around that design  Using the static keyword is kind of like saying   Hey  this function I m defining doesn t need any context state  it can just be called   Since your Add function is very simple  this makes sense  As you start diving deeper into OOP  you re going to find that your functions get more complicated and rely on knowing their state context   My advice  Pick up an OOP book and get ready to switch your brain from functional programming to OOP programming  You re in for a ride

User · Answer

you have to make you re function static like this  namespace Add Function     class Program         public static void string   args               int a         int b         int c          Console WriteLine  Enter value of  a             a   Convert ToInt32 Console ReadLine             Console WriteLine  Enter value of  b             b   Convert ToInt32 Console ReadLine               why can t I not use it this way         c   Add a  b          Console WriteLine  a   b    0    c             public static int Add int x  int y                int result   x   y          return result                 you can do Program Add instead of Add you also can make a new instance of Program by going like this  Program programinstance   new Program

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