32
Thinking Cap Implementation
➊In the heading, the function’s name is preceded by the
class name and :: – otherwise C++ won’t realize this
is a class’s member function.
void ThinkingCap::slots(char new_green[ ], char new_red[ ])
{
assert(strlen(new_green) < 50);
assert(strlen(new_red) < 50);
strcpy(green_string, new_green);
strcpy(red_string, new_red);
}
33
Thinking Cap Implementation
➋Within the body of the function, the class’s member
variables and other member functions may all be
accessed.
void ThinkingCap::slots(char new_green[ ], char new_red[ ])
{
assert(strlen(new_green) < 50);
assert(strlen(new_red) < 50);
strcpy(green_string, new_green);
strcpy(red_string, new_red);
}
34
Thinking Cap Implementation
➋Within the body of the function, the class’s member
variables and other member functions may all be
accessed.
void ThinkingCap::slots(char new_green[ ], char new_red[ ])
{
assert(strlen(new_green) < 50);
assert(strlen(new_red) < 50);
strcpy(green_string, new_green);
strcpy(red_string, new_red);
}
But, whose member
variables are
these? Are they
student.green_string
student.red_string
fan.green_string
fan.red_string
?
35
Thinking Cap Implementation
➋Within the body of the function, the class’s member
variables and other member functions may all be
accessed.
void ThinkingCap::slots(char new_green[ ], char new_red[ ])
{
assert(strlen(new_green) < 50);
assert(strlen(new_red) < 50);
strcpy(green_string, new_green);
strcpy(red_string, new_red);
}
If we activate
student.slots:
student.green_string
student.red_string
36
Thinking Cap Implementation
➋Within the body of the function, the class’s member
variables and other member functions may all be
accessed.
void ThinkingCap::slots(char new_green[ ], char new_red[ ])
{
assert(strlen(new_green) < 50);
assert(strlen(new_red) < 50);
strcpy(green_string, new_green);
strcpy(red_string, new_red);
}
If we activate
fan.slots:
fan.green_string
fan.red_string
37
Thinking Cap Implementation
void ThinkingCap::push_green
{
cout << green_string << endl;
}
Here is the implementation of the push_green
member function, which prints the green message:
38
Thinking Cap Implementation
void ThinkingCap::push_green
{
cout << green_string << endl;
}
Here is the implementation of the push_green
member function, which prints the green message:
Notice how this member function implementation
uses the green_string member variable of the object.
39
A Common Pattern
❐Often, one or more member functions will
place data in the member variables…
class ThinkingCap {
public:
void slots(char new_green[ ], char new_red[ ]);
void push_green( ) const;
void push_red( ) const;
private:
char green_string[50];
char red_string[50];
};
❐…so that other member functions may use that
data.
slots push_green & push_red
40
❐Classes have member variables and member
functions. An object is a variable where the data
type is a class.
❐You should know how to declare a new class type,
how to implement its member functions, how to
use the class type.
❐Frequently, the member functions of an class type
place information in the member variables, or use
information that’s already in the member variables.
❐In the future we will see more features of OOP.
Summary
41
THE END
Presentation copyright 1997, Addison Wesley Longman
For use with
Data Structures and Other Objects Using C++
by Michael Main and Walter Savitch.
Some artwork in the presentation is used with permission from Presentation Task Force
(copyright New Vision Technologies Inc.) and Corel Gallery Clipart Catalog (copyright