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:
// my first program in c++
#include <iostream.h>
int main()
{
std::cout << "Hello World";
}Let’s examine this program line by line:
Line 1 : // my first program in c++
Two slash sign 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. Programmer 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 <iostream.h>
In a program, 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 <iostream.h>, instructs the preprocessor to include a section of standard C++ code, known as header iostream, that allows to perform standard input and output operations, such as writing the output of the program (Hello World) to the screen
Line 3 : A Blank Line
Blank lines have no effect on the program. They simply improve readability of the code.
Line 4 : int main()
This line initiates the declaration of the function. Essentially, a function is a group code statements which are given a name: in this case, the gives the name “main” to the group of code statements that follow. Functions will be discussed in details in a later chapter, but essentially, their definition is introduced with a succession of a type (int), a name (main) and a pair of parentheses ( () ), optionally including parameters.
The function names main is the 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.
Line 5 and 7: {and}
The Open braces at line 5 ( { ) indicates the beginning of main’s function definition, and the closing braces ( } ) at line 7, indicates its end. Everything between these braces is the function’s body that defines what happens when main is called. all Function uses braces to indicate the beginning and end of their definitions.
Line 6 : std::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 the program, specifying its actual behavior. Statement are executed in the same order that they appear within the function’s body.
This statement has three parts: First, std::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 std::cout. Finally, a sentence within quotes (“Hello World”) is the content inserted into standard output.
Notice that the statement ends with a semicolon (;). This character marks the end of the statements, 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