Function Declarations

A function declaration tells the compiler about a function name and how to call the function. The actual body of the function can be defined separately.

A function declaration has the following parts:

return_type function_name( parameter list );

For the above defined function max(), following is the function declaration: 

int max(int num1, int num2);

 
Parameter names are not important in function declaration only their type is required, so following is also valid declaration:

int max(int, int);

 
Function declaration is required when you define a function in one source file and you call that function in another file. In such case you should declare the function at the top of the file calling the function.