Function Declaration and Definition

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Function Declaration and Definition

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1. Similar to variable , C Program has to declare function
2. Function Declaration is Called as 'Function Prototype'
3. As variables are declared before use , similarly the 'Function Prototype' is declared before using it.
4. It Provide following information to the Compiler

                >  Name of the Function
                >  Return Type [ Optional / Default-Integer ]
                > Argument List / Parameter List

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Note :

• Prototype always ends with semicolon
• Parameter List is Optional
• Default Return Type is Integer
  

Syntax :       return_type function_name ( type arg1, type arg2...... );

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Valid Examples : 

1. int sum ( int a ,int b); 
   
2. int square ( int a );  
3. void display(void);
4. int sum (int,int); 
   

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Facts about Prototype Declaration :

1. If function Definition is Written after main then and then only we write Prototype Declaration in Global Declaration Section
   
2. If function Definition is written above the main function then , no need to write  Prototype Declaration

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