Lets understand each and every thing in detail :-

1. // indicates that everything following it until the end of the line is a comment: it is ignored by the compiler. Another way to write a comment is to put it between /* and */ (e.g. x = 1 + /*sneaky comment here*/ 1;). A comment of this form may span multiple lines. Comments exist to explain non-obvious things going on in the code. Use them: document your code well!

2. Lines beginning with # are preprocessor commands, which usually change what code is actually being compiled. #include tells the preprocessor to dump in the contents of another file, here the iostream file, which defines the procedures for input/output.

4. int main() {...}defines the code that should execute when the program starts up. The curly braces represent grouping of multiple commands into a block. More about this syntax in the next few lectures.
5. • cout << : This is the syntax for outputting some piece of text to the screen.

• Namespaces: In C++, identifiers can be defined within a context – sort of a directory of names – called a namespace. When we want to access an identifier definedin a namespace, we tell the compiler to look for it in that namespace using the scope resolution operator (::). Here, we’re telling the compiler to look for cout in the std namespace, in which many standard C++ identifiers are defined.
A cleaner alternative is to add the following line below line 2:
using namespace std;
This line tells the compiler that it should look in the std namespace for any identifier we haven’t defined. If we do this, we can omit the std:: prefix when writing cout. This is the recommended practice.

• Strings: A sequence of characters such as Hello, world is known as a string.A string that is specified explicitly in a program is a string literal.

• Escape sequences: The \n indicates a newline character. It is an example of an escape sequence – a symbol used to represent a special character in a text literal. Here are all the C++ escape sequences which you can include in strings:

Escape sequences

7. return 0 indicates that the program should tell the operating system it has completed successfully. 

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