Introductions

Course Logistics

Who is your instructor. Who is your section leader. Role of the website. Course Policy and CS Department Honor Policy. Computing resources and course VM.

What is this course about?

This course is an introduction to programming. C++ is the language we use, but this course is not about learning C++.

It is about learning to program!

"How to program" is bigger than "C++" or any other language.

Programming is a creative process, in which you construct a model world inside the computer that interacts with the real world via keyboards, mice, monitors, speakers network connections, and so forth. It's very rewarding and exciting; you will never be bored!
However, it is frustrating at the same time.
- With probability 99.9%, your code won't work at one shot; you need to debug your code, figuring out where you were wrong.
- Again unfortunately, with probability 99.9%, the debugging won't be finished at one shot. After several trials (sometimes, tens or even hundreds of trials, depending on the program size), your program will finally work.
- Well, actually, you don't know for sure whether the program works correctly. What you know is that the program works correctly on several tested cases. There may be several tricky cases in which your program will crash, or your program may be have some vulnerability that may be exploited by hackers!
In summary, it's just hard to write a correct (and secure) program. Some words of advice:
- Make friends with frustration. Welcome it with your open arms.
- You are learning something, when you get frustrated.
Of course, we will try our best so that the level of frustration may stay manageable by you. We are going to start slow.
IMPORTANT: If you think you're too frustrated, you must seek for help. It's your responsibility to seek for help. It's our responsibility to help you with all our might when you seek help. We can't really know whether you're desperate.

This course focuses on solid understanding of foundational concepts, so please be patient with the fact that your programs will usually be reading and writing text and not interacting with all the fancy peripherals mentioned above. You'll apply your programming skills to fun graphic stuff next semester: this semester we focus on programming itself.

Compiled vs interpreted, and why C++ is different than Javascript

You really should review the computer architecture section of SY110. Here's a link to the SY110 site.

In SY110, all of you were exposed to Javascript programs. You'll notice that what we do here feels a lot more low-level, and requires a lot more discipline. The main reason is that Javascript programs are executed by the browser, whereas C and C++ programs are actually executed by the physical machine. This fundamental fact leads to a lot of the differences you'll observe.

Javascript is an interpreted language. This means that the code you write is read and processed by the browser, which then executes the steps demanded by that code.

C and C++ are compiled languages. As shown in the figure below, this means that the code you write is read and processed by a special-purpose program called a compiler, which translates it into the zeros and ones that the CPU speaks, and stores it in an executable file. At some later point, the OS is told to start the program stored in the executable file running, and the CPU initiates its fetch-decode-execute cycle on the code contained in that file.

	Step 1: Source code writing. Use an editor to create the file `hello.cpp` containing the source code for the program.
	Step 2: Compilation. Use a compiler (g++ in this case) to translate the human-readable C++ source code into machine-readable object code `hello.o`.
	Step 3: Linking. Use a linker (g++ does this as well) to combine our object file `hello.o` with other object files (like those that take care of input/output) to create the executable program `hello`.
	Step 4: Execution. Use the OS to initiate execution of (i.e. start the fetch-decode-execute cycle on) the program `hello`.

All these steps are kind of a pain in the neck, but remember: we're writing a program that is executing on "bare metal", i.e. directly on the CPU.

http://xkcd.com/303/

Problems

At the end of the notes for almost every lecture will be a couple of example problems with solutions. Everyone likes to see examples of code, so that's what we give you!

Do you know ...

How are Javascript and C++ different?
What are four steps you need to go through, when you write a program with the C++ programming language?