Introduction to C++

The best way to learn a programming language is by writing programs. Typically, the first program beginners write is a program called "Hello World", which simply prints "Hello World" to your computer screen. Although it is very simple, it contains all the fundamental components C++ programs have:

The left panel above shows the C++ code for this program. The right panel shows the result when the program is executed by a computer.



Let's examine this program line by line:
Line 1: // my first program in C++ Two slash signs indicate that the rest of the line is a comment inserted by the programmer but which has no effect on the behavior of the program. Programmers use them to include short explanations or observations concerning the code or program. In this case, it is a brief introductory description of the program.

Line 2: #include Lines beginning with a hash sign (#) are directives read and interpreted by what is known as the preprocessor. They are special lines interpreted before the compilation of the program itself begins. In this case, the directive #include , instructs the preprocessor to include a section of standard C++ code, known as header iostream.h, that allows to perform standard input and output operations, such as writing the output of this program (Hello World) to the screen.

Line 3: void main () This line initiates the declaration of a function. Essentially, a function is a group of code statements which are given a name: in this case, this gives the name "main" to the group of code statements that follow. The function named main is a special function in all C++ programs; it is the function called when the program is run. The execution of all C++ programs begins with the main function, regardless of where the function is actually located within the code.

Lines 4 and 6: { and } The open brace ({) at line 4 indicates the beginning of main's function definition, and the closing brace (}) at line 6, indicates its end. Everything between these braces is the function's body that defines what happens when main is called. All functions use braces to indicate the beginning and end of their definitions.

Line 5: cout << "Hello World"; This line is a C++ statement. A statement is an expression that can actually produce some effect. It is the meat of a program, specifying its actual behavior. Statements are executed in the same order that they appear within a function's body. This statement has three parts: First, cout, which identifies the standard character output device (usually, this is the computer screen). Second, the insertion operator (<<), which indicates that what follows is inserted into cout. Finally, a sentence within quotes ("Hello world"), is the content inserted into the standard output. Notice that the statement ends with a semicolon (;). This character marks the end of the statement, just as the period ends a sentence in English. All C++ statements must end with a semicolon character. One of the most common syntax errors in C++ is forgetting to end a statement with a semicolon.