Functions in C

A function is a group of statements that together perform a task. Every C program has at least one function, which is main().

But Why do we use Function ?

There are several number of advantages of using a function in a program. Some of them  are:-

• It breaks the code into smaller Functions and keeps the program organized
• It makes the program easier to understand to the end_user.
• It makes easy to detect any "error" if any present in the program i.e,reduces chances of error.
• It avoid repetition of the code.

These above are the some of the advantages of the function in a program.

A function is divided into three parts:-
⇒ Function Declaration
⇒Function Definition
⇒Function Call

Flow Chart

There are total four types of Syntax for a function.

1. No return type with No argument
   
   Syntax: #include<stdio.h>
                  void fun( ); //here fun() is a function name
                  void main( )
                  {
                   ........................................
                   ........................................
                   ........................................
                   fun( ); //function call         
                   ........................................
                   }
                
                  void fun( )
                  {
                   ........................................
                   ........................................
                  }
2. No return type with argument         
   
   Syntax: #include<stdio.h>
                  void fun(datatype, datatype); //datatype can be int, float, char, etc
                  void main( )                                   
                  {
                   ........................................
                   ........................................
                   ........................................
                   fun( ); //function call
                   }
                
                  void fun(datatype_variable, datatype_variable)
                  {
                   ........................................
                   ........................................
                  }
                 
3. Return type with argument
   Syntax: #include<stdio.h>
                  int fun(datatype, datatype); //fun( ) is the name of function
                   int main( )
                  {
                   ........................................
                   ........................................
                   ........................................
                   fun( ); //function call
                   ........................................
                   return 0;
                   }
                
                   int fun(datatype_variable, datatype_variable)
                  {
                   ........................................
                   ........................................
                   return 0;
                  }
4. Return type with No argument
   Syntax: #include<stdio.h>
                int fun( ); //here fun( ) is a function name
                int main( )
                {
                ........................................
                ........................................
                ........................................
                 fun( );
                 .......................................
                 return 0;
                }
   
                int fun( ) //here the datatype is int
                {
                ........................................
                ........................................
                return 0;
                }

So, here are the syntax used in a function as per the requirement.

ACTUAL ARGUMENT :- 
Is somewhat giving values to the formal argument by writing the values.
for example- fun(5,2);


FORMAL ARGUMENT :-
Are the argument used to/for the declaration of the function.
for example- fun(int x, int y);

Function can be called by the value or by the reference and the most common way to call a function is by call by value.

# Call by Value

• In this the value of actual argument is called by formal argument.
• Whatever changes made in the function definition are not "reflected back" in the main( ).
  for example:-
  

  

  Example 1

# Call by Reference

• Address of actual argument is passed to formal argument.
• Whatever changes made in the function definition are "reflected back" in the main().
  for example:-

  

  Example 2

  In call by reference Pointers were used. Pointer are those variables that can store another variable's address.

Things to Remember

• main( ) function is compulsory for any C program.
• Anything written before " ( ) " is the name of the function.
• It doesn't matter whether you first write the different function and then write about the main( ) function, the compiler will first go to main( ) function.
• A variable used in a function has the scope and lifetime up to that function only i.e, that variable can't be used as same as(value & behavior) in the original functions.
  
  
  To read our post on Recursion, please click on Rec( ).
  To read our post on Array (Part-1) please click on Arr1.
  
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