Declaration Code is the code you use to declare your member variables in the class. Only the memory variables listed here are available within the class. If a member variable is an array, you would DECLARE the array in this section of code.
Another important piece in this section is the declaration of PROTECTED members. A protected member is a member variable that is not visible outside of the class. In other words, methods within the class can access and modify that variable but the variable does not exist as far as the outside world (anything that is not a method of the class) is concerned.
An example of a member variable that would be declared PROTECTED would be a member that saves the state of the environment when the object is instantiated. The variable may be used to reset the environment when the object is released but it serves no purpose to programs instantiating the object and interacting with it. As a matter of fact, you would not want this member variable to be changed by the outside world. Hence, you would PROTECT it in the declaration section of code.