Notes for Tuesday 18 January

Programming a computer is a tremendously valuable skill, but it takes a lot of practice and patience. Try to work a little every day (and a lot some days!) and don't get discouraged if it starts to feel difficult. Although some people will make

In particular don't get discouraged by mistakes. Mistakes are how we learn. Remember that compiler errors are routine – sure, there's a mistake, but it doesn't reflect badly on you. Just systematically start finding and fixing it. Professional programmers with decades of experiences see hundreds of errors every single day.

If you feel like you're getting lost, do not hesitate to seek help from me. I try to be very accessible, in office hours, by appointment, or over IM. Because everything we learn builds on everything that came before, any problem you're having will get better only with additional practice and expert assistance. It will not get better on its own!

Here we will keep instructions on getting a simple program to run on various compiler systems. For Windows users, I'm recommending Visual C++ Express Edition. In the lab, we have Visual Studio 2008. For the Mac, get Apple's XCode developer tools. Other configuratinos are possible. If you find directions for some system not listed here, do send them to me.

Here is the sample program we'll use. You can also start with this for Assignment 1.

#include <stdio.h>

int main()
{
    printf("Hello, world!\n");
    return 0;
}

Here are some of the concepts we covered about the sample program today. They are probably incomplete.

• include means to bring in functionality (called a library) from somewhere else. In this case, stdio.h refers to the standard input/output library, which is the home of printf.
• main() is the name of a function, or procedure, which is a sequence of steps to execute. The parentheses indicate that it's a function, which is why we need them even though, in this case, they're empty. The name main is special, because it is used as the “entry point” of the program — it all starts here. Later on we'll have additional functions with other names.
• The curly brackets {} (also called braces) indicate the beginning and end of a block of code. They show the extent of the main procedure.
• The printf is how we do formatted output. It is a function (you can tell because of the parentheses) from the standard input/output library.
• The double quotes indicate a string or sequence of characters. Because they are provided to printf, these are the characters that will appear on the screen when it runs.
• One of the characters is special: it consists of the sequence backslash, then lowercase 'n': \n This is called a new line character. It tells the output to go on to the next line, much like hitting return or enter in a word processor.
• Finally, return is a keyword (there are no parentheses, so it cannot be a function) that means we are finished with the current function. At this point, because the function we're talking about is main, the program ends. If you were to include extra code after return, it would not be executed.
• Note also the semi-colons. There are semi-colons on statements within the block (between the curly braces), but not on the curly braces themselves, and not on the main() declaration, and not on the #include. If you forget a semi-colon, the compiler will definitely let you know. However, if you put one where it is not supposed to go, it could happen that the compiler won't notice but the program also won't work right! We'll see examples of that insidious problem later.

Identifiers are how we name things in a program. main and printf are examples of identifiers. They both name functions: one defined in this program, and one included from stdio.h.

Identifiers must start with a letter (upper or lower case) or an underscore character (shift-hyphen). Following the first character, they can contain letters, numbers, or underscore. They may not contain spaces. However, we often use the underscore to separate words that are part of the same identifier, for readability, as in: quiz_2_average or parking_ticket_amount.

Identifiers are case-sensitive, which means that it matters whether upper- or lower-case letters are used. Quiz and QUIZ and quiz and qUiZ are all valid identifiers but they are different identifiers. You cannot type Quiz in one place and then expect quiz to work in another.

Because programming languages are picky, it's important to configure a good font, and make it big enough, so that characters like 0 (zero), O (capital O), 1 (one), l (lowercase l), ; (semi-colon), and : (colon) are sufficiently distinguishable.

In Visual Studio, you can configure this under Tools » Options » Fonts & Colors. It's also recommended to use a fixed-width (monospace) font (they were the bold ones in Visual Studio). A reasonable choice is “Consolas”.