Declaration of function in c
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.