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Introduction to C
This tutorial designed to be a stand-alone introduction to C, even if you've never programmed before. However, because C++ is a more modern language, if you're not sure if you should learn C or C++, I recommend the C++ tutorial instead, which is also designed for people who have never programmed before. Nevertheless, if you do not desire some of C++'s advanced features or simply wish to learn C instead of C++, then this tutorial is for you!
Getting set up - finding a C compiler
The very first thing you need to do, before starting out in C, is to make sure that you have a compiler. What is a compiler, you ask? A compiler turns the program that you write into an executable that your computer can actually understand and run. If you're taking a course, you probably have one provided through your school. If you're starting out on your own, your best bet is to use Code::Blocks with MinGW. If you're on Linux, you can use gcc, and if you're on Mac OS X, you can use XCode. If you haven't yet done so, go ahead and get a compiler set up--you'll need it for the rest of the tutorial.
Intro to C
Every full C program begins inside a function called "main". A function is simply a collection of commands that do "something". The main function is always called when the program first executes. From main, we can call other functions, whether they be written by us or by others or use built-in language features. To access the standard functions that comes with your compiler, you need to include a header with the #include directive. What this does is effectively take everything in the header and paste it into your program. Let's look at a working program:
#include <stdio.h>
int main()
{
printf( "I am alive! Beware.\n" );
getchar();
return 0;
}
Let's look at the elements of the program. The #include is a "preprocessor" directive that tells the compiler to put code from the header called stdio.h into our program before actually creating the executable. By including header files, you can gain access to many different functions--both the printf and getchar functions are included in stdio.h. The semicolon is part of the syntax of C. It tells the compiler that you're at the end of a command. You will see later that the semicolon is used to end most commands in C.
The next important line is int main(). This line tells the compiler that there is a function named main, and that the function returns an integer, hence int. The "curly braces" ({ and }) signal the beginning and end of functions and other code blocks. If you have programmed in Pascal, you will know them as BEGIN and END. Even if you haven't programmed in Pascal, this is a good way to think about their meaning.
The printf function is the standard C way of displaying output on the screen. The quotes tell the compiler that you want to output the literal string as-is (almost). The '\n' sequence is actually treated as a single character that stands for a newline (we'll talk about this later in more detail); for the time being, just remember that there are a few sequences that, when they appear in a string literal, are actually not displayed literally by printf and that '\n' is one of them. The actual effect of '\n' is to move the cursor on your screen to the next line. Again, notice the semicolon: it is added onto the end of all lines, such as function calls, in C.
The next command is getchar(). This is another function call: it reads in a single character and waits for the user to hit enter before reading the character. This line is included because many compiler environments will open a new console window, run the program, and then close the window before you can see the output. This command keeps that window from closing because the program is not done yet because it waits for you to hit enter. Including that line gives you time to see the program run.
Finally, at the end of the program, we return a value from main to the operating system by using the return statement. This return value is important as it can be used to tell the operating system whether our program succeeded or not. A return value of 0 means success.
The final brace closes off the function. You should try compiling this program and running it. You can cut and paste the code into a file, save it as a .c file, and then compile it. If you are using a command-line compiler, such as Borland C++ 5.5, you should read the compiler instructions for information on how to compile. Otherwise compiling and running should be as simple as clicking a button with your mouse (perhaps the "build" or "run" button).
You might start playing around with the printf function and get used to writing simple C programs.
Explaining your Code
Comments are critical for all but the most trivial programs and this tutorial will often use them to explain sections of code. When you tell the compiler a section of text is a comment, it will ignore it when running the code, allowing you to use any text you want to describe the real code. To create a comment in C, you surround the text with /* and then */ to block off everything between as a comment. Certain compiler environments or text editors will change the color of a commented area to make it easier to spot, but some will not. Be certain not to accidentally comment out code (that is, to tell the compiler part of your code is a comment) you need for the program.
When you are learning to program, it is also useful to comment out sections of code in order to see how the output is affected.
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