CSCI-1200/labs/02_classes/README.md

Overview

In this lab, you will be writing your own C++ classes. We have not covered C++ classes in the lecture, but according to last Friday's poll, everyone is this class has either experience in Java or experience in Python, so the concept of class is not new to you. To get familiar with the C++ syntax on classes, you are recommended to quickly review the following 3 files:

date.h
date.cpp
date_main.cpp

Some notes about these 3 files:

• date.h and date.cpp are the implementation of a class called date.
• date_main.cpp is the program to test the date class, and therefore, only this file contains the main function.
• the file with the .h file name extension is called the header file, and the .cpp file is callled the implementation file. Note that in C++ the name of the header and implementation files are not required to exactly match the name of the class, but it is good coding style to do so.
• in this lab, you're not required to use the keyword const, as we will cover more about it in lecture. For the same reason, for now, you can also ignore the keyword const that is used in the date class.
• typically in C++, we declare a class in the header file, and then define/implement this class in a .cpp file. The declaration of a class includes the prototype of its member functions, and it also includes the member variables of this class. As can be seen from date.h and date.cpp, the date class has 3 member variables:

  int day;
  int month;
  int year;

and it has several member functions. Take the isLeapYear function for example, we write its prototype in the header file as below:

bool isLeapYear() const;  

and we define it in the .cpp file as following:

bool Date::isLeapYear() const {
  return (year%4 ==0 && year % 100 != 0) || year%400 == 0;
}

pay attention to the "Date::" right in front of the function name isLeapYear. The "Date::" defines the scope of this function, meaning that this function is a member function of the Date class.

• typically in C++, we declare member variables as private, and declare member functions as "public". Member functions allows user to operate on these member variables, which can not be accessed directly from outside the class, and that is the meaning of private.
• constructor:

Checkpoint 1

estimate: 15-25 minutes

For the first checkpoint, you will be working in groups of 4 to design the Animal.h file for a new class. Keep in mind that you should only put the class defintion in the header file, you are not writing the actual implementation. Make sure that everyone in the group participates and understands the material - it is possible that all of you will have to answer questions to get checked off!

Each instance of the Animal class will describe several characteristics about an animal. Every Animal must have a name at all times. This is the only value that will be passed in when a new object is declared. It should be possible to set the weight of the animal, if the animal can survive on land, if the animal can survive in water, if the animal eats meat, and if the animal eats plants. All of these values (including the name) should be accessible from outside the class as well. In addition, the class should be able to indicate if the animal in question is an omnivore (eats both meat and plants) and if they are amphibious (can survive on land and in water).

Make sure to explain the purpose of every function with a comment. Consider the return type, whether each argument should be passed by value, reference. Be prepared to justify your choices. To get checked off, show your completed header file and answer any questions asked by the TA/mentor.

Note: Only Checkpoint 1 is a team exercise. For the rest of this lab, you will implement a simple C++ class named Time. It represents all possible times in a 24-hour period, including hours, minutes and seconds. An immediate representation issue is how to handle morning (am) and afternoon (pm) times. We could have a separate bool indicating whether the time is am or pm. It is easier, however, to represent the hours in military time. This means that the hours of the day are numbered from 0 to 23, with 13 being 1 pm, 14 being 2 pm, etc.

Checkpoint 2:

estimate: 30 minutes

In the second checkpoint you will get started by implementing the initial class design, several member functions, and a simple main program to test your class.

The instructions below describe how to build your executable from the command line using g++ or clang++ using the WSL or UNIX terminal. Even if you plan to use Visual Studio or another IDE for the bulk of your work this semester, you are required to also show that you can successfully build and run this lab using g++ from a terminal on your own machine.

• We provide basic testing code in main.cpp. You’ll need to create 2 new empty code files named time.h and time.cpp.

• Begin work on time.h. Within the file, declare a class called Time. Follow the form and syntax of the Date class. Read the syntax carefully (such as the semi-colon at the end of the class declaration). Add private member variables for the hour, minute and second. In the public area of the class, declare two constructors: one, the default constructor, should initialize each of the member variables to 0; the other, having three arguments, accepts initial values for the hour, minute and second as function call arguments. Declare member functions to access the values of the hour, the minute and the second (three different member functions). Don’t write the body of any of the functions in the time.h file. Save all the implementation for the time.cpp file.

• Review the provided main.cpp. Note that we must #include "time.h" in addition to including #include <iostream>. (Note: We use angle brackets for standard library includes and double quotes for our custom header files in the working directory.) The main program creates multiple Time objects, using the two different constructors and uses the functions that access the values of hour, minute and second by printing the two times.

Note: There is a common confusion when creating a new variable using the default constructor:

Time t1(5,30,59); // calls the non-default constructor w/ 3 integer arguments
Time t2(); // COMPILE ERROR - a buggy attempt to call the default constuctor
Time t3; // the *correct* way to call the default constructor

Now implement all of the class constructors and member functions in the file time.cpp. Don’t forget to add the line to #include "time.h". Any file that uses or implements Time functionality must include the Time class header file.

Now, compile your program and remove errors. Here’s where the difference between compiling and linking matters.

When compiling using g++ on the command line, the two separate command lines:

g++ -c main.cpp -Wall -Wextra
g++ -c time.cpp -Wall -Wextra

compile the source code to create two object code files called main.o and time.o separately. The -c means “compile only”. Compiler errors will appear at this point. If there are errors in main.cpp (or time.cpp), then the files main.o (or time.o) will not be created. Use the ls command to check.

Important Note: We only compile .cpp files. We do not directly compile header files. Header files are compiled only indirectly when included in a .cpp file.

Once you have driven out all of the compiler errors, you can “link” the program using the command:

g++ main.o time.o -o time_test.exe

to create the executable called time_test.exe. If you have not defined all of the necessary member functions in the Time class, then you would see “linking” errors at this point. You can combine all three command lines (compiling each of the 2 .cpp files to 2 object files and linking all object files) with this command:

g++ main.cpp time.cpp -o time_test.exe -Wall -Wextra

Which is more similar to what we did last lab. Equivalently, if those are the only two .cpp files in the current directory, you can compile and link using the command line wildcard:

g++ *.cpp -o time_test.exe -Wall -Wextra

Note that this will not create the intermediate .o files and will only proceed to the linking step if the two files compile cleanly.

To complete this checkpoint: Show compilation of the program using g++/clang++ within the WSL or UNIX terminal, with all compiler errors removed and demonstrate correct execution of your program. Yes, please show us you can compile from the terminal with g++, even if you plan to primarily use Visual Studio or another IDE for the rest of the semester.

Checkpoint 3

estimate: 20-30 minutes

Create and test a few more member functions. This will require modifications to all three of the files. You should uncomment the provided tests in main.cpp as you work, and add your own tests.

• setHour, setMinute, setSecond. Each should take a single integer argument and change the appropriate member variable. For now, do not worry about illegal values of these variables (such as setting the hour to 25 or the minute to -15). Assume whoever calls the functions does the right thing. In general, this is a bad assumption, but we will not worry about it here.
• PrintAmPm prints time in terms of am or pm, so that 13:24:39 would be output as 1:24:39 pm. This member function should have no arguments. Note that this requires some care so that 5 minutes and 4 seconds after 2 in the afternoon is output as 2:05:04 pm. The output should be to std::cout.

To complete this checkpoint: Show a TA your tested and debugged extensions. Be prepared to discuss your implementation.