The remainder of this chapter presents seven simple examples that demonstrate the concepts we introduced in the context of the car analogy. These examples, summarized below, incrementally build a GradeBook class to demonstrate these concepts:
- The first example presents a GradeBook class with one member function that simply displays a welcome message when it is called. We then show how to create an object of that class and call the member function so that it displays the welcome message.
- The second example modifies the first by allowing the member function to receive a course name as a so-called argument. Then, the member function displays the course name as part of the welcome message.
- The third example shows how to store the course name in a GradeBook object. For this version of the class, we also show how to use member functions to set the course name in the object and get the course name from the object.
- The fourth example demonstrates how the data in a GradeBook object can be initialized when the object is createdthe initialization is performed by a special member function called the class's constructor. This example also demonstrates that each GradeBook object maintains its own course name data member.
- The fifth example modifies the fourth by demonstrating how to place class GradeBook into a separate file to enable software reusability.
- The sixth example modifies the fifth by demonstrating the good software-engineering principle of separating the interface of the class from its implementation. This makes the class easier to modify without affecting any clients of the class's objectsthat is, any classes or functions that call the member functions of the class's objects from outside the objects.
- The last example enhances class GradeBook by introducing data validation, which ensures that data in an object adheres to a particular format or is in a proper value range. For example, a Date object would require a month value in the range 112. In this GradeBook example, the member function that sets the course name for a GradeBook object ensures that the course name is 25 characters or fewer. If not, the member function uses only the first 25 characters of the course name and displays a warning message.
Note that the GradeBook examples in this chapter do not actually process or store grades. We begin processing grades with class GradeBook in Chapter 4 and we store grades in a GradeBook object in Chapter 7, Arrays and Vectors.