CSCI 261 Programming Concepts (C++)

Homework 31: Addresses and Value Storage

Concepts

For this assignment, focus on using the reference ("address of") operator.

The Importance of Understanding Memory

One benefit of using higher level languages is that they free the programmer from needing to worry about telling the machine how to store and manage memory. C++ is a high level language, but it also provides us the ability to inspect and manage memory directly, via pointers and references. Being able to manage the storage of values in memory is a critical requirement for more advanced programs (such as those you will see in CSCI 262).

More importantly, however, it is critical to know how our programs interact with memory.

"Why?" you ask, "I can write useful programs and not care about memory addresses and how they work!" This is very true. But consider your fancy car that you might need to take to a mechanic. What if that mechanic told you, "I have no idea how cars work, but I sure can fix yours!" How much trust would you put in that mechanic? As software engineers, we must obtain a deeper understanding of how our programs work in order to be most effective and to eventually create more powerful programs (just as a mechanic needs to know how the car works in order to, say, build his/her own supercar).

Values and Memory

In class we demonstrated the ideas of the stack and the heap and how data (values named by variables) are stored in memory. To help illustrate this, we will start with learning how to use the & operator, which is a little tricky because it tends to mean something different depending on the context. For example, you have seen this &operator in the context of function definitions:

In this context, we're telling the compiler that "battle is a function that accepts two trolls by reference." To elaborate, we're really stating that this function to not pass a copy of two trolls when called; rather, it should expect to receive two references to two Troll objects that are defined by the caller.

In another, more pure, context, you use the & operator to obtain the memory address of where something is stored. For example:

On the first line above, we're saying that fred is a Troll object. On the second line, we're using the & operator to say, "give me the memory address where the Troll fred is stored, and print that address." Simple!

In a nutshell, you should realize that & is an unary operator that simply returns the memory address of its operand.

Instructions

For this assignment, we'd like you to simply apply the & operator to illustrate the memory addresses of things stored in memory, and to gain an understanding of hexadecimal representation of numbers. In class you saw how hex numbers are really just shorthand for their binary equivalents. More importantly, when completing this assignment you should read the addresses that are printed to the screen, and notice their relationship to one another.

Write a program that:

• Creates a static const int, an int, a double, a String, and a Dog. You may assign any values you like to these variables (in the case of the Dog, merely instantiate a "default" Dog).
• Prints the address of each of these values to the screen.

When run, your program should display something that looks like this:

Note that your addresses will definitely be different. Your variable names and their values are up to you.

While the code for this assignment is rather trivial, you should ask yourself:

• Why is the static value's address so different from the others?
• Focusing on the last few hex digits, why are the addresses what they are, and how do they allude to the amount of memory each value occupies?

Lastly, realize this is a syntax exercise to prepare you for our upcoming assignment with pointers.

Requirements and Rubric

This work is worth 110 points.

Concepts Exercised: classes, OOP, memory, datatypes

© 2012 Yong Joseph Bakos.