HowToProgramC : Lesson 2

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First C Program:

The best way to learn C is to start coding right away. So here is our very first program in C.

# include <iostream.h>
cout << "HELLO WORLD!";

Let's see what the above snippet of code means.

# include
#include is a pre-processor directive. It is not part of our program; it is an instruction to the compiler. It tells the C compiler to include the contents of a file, in this case the system file iostream.h. The compiler knows that it is a system file, and therefore looks for it in a special place. The features of preprocessor will be discussed later. For the time being take this line on faith. You have to write this line. The sign # is known as HASH and also called SHARP.

<iostream.h> is the name of the library definition file for all Input Output Streams. Your program will almost certainly want to send stuff to the screen and read things from the keyboard. iostream.h is the name of the file which has the code to do that work for you.

The name main is special, in that the main is actually the one which is run when your program is used. A C program is made up of a large number of functions. Each of these is given a name by the programmer and they refer to each other as the program runs. C regards the name "main" as a special case and will run this function first. If you forget to have a main function, or mistype the name, the compiler will give you an error.

Notice that there are parentheses (“( )”, normal brackets) with main. Here the parentheses contain nothing. There may be something written inside the parentheses. It will be discussed in later lectures.

Next, there is a curly bracket also called braces("{ }"). For every open brace there must be a matching close. Braces allows to group together pieces of a program. The body of main is enclosed in braces. Braces are very important in C; they enclose the blocks of the program.

cout is known as out put stream in C and C++. Stream is a complicated thing, you will learn about it later. Think of a stream as a door. The data is transferred through stream, cout takes data from computer and sends it to the output. For the moment it is a screen of the monitor. hence we use cout for output.

The sign << indicates the direction of data. Here it is towards cout and the function of cout is to show data on the screen.

The thing between the double quotes (“ ”) is known as character string. In C programming character strings are written in double quotes. Whatever is written after << and within quotation marks will be direct it to cout, cout will display it on the screen.

The semicolon (;) at the end of the above statement is very important. All C statements end with a semicolon (;). Missing of a semicolon (;) at the end of statement is a syntax error and compiler will report an error during compilation. If there is only a semicolon (;) on a line than it will be called a null statement. i.e. it does nothing. The extra semicolons may be put at the end but are useless and aimless.

Comments in C:

Commenting the code is very much encouraged in almost every programming language. The syntax of commenting the C code is as under:

// for single line comments.....

/* This is a block of comments.
The comments end here.....*/

Comments do not add to the exe file, so use them liberally.

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