When we consider a C++ program, it can be defined as a collection of objects that communicate via invoking each other's methods. Let us now briefly look into what do class, object, methods and instant variables mean.
Object - Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors - wagging, barking, eating. An object is an instance of a class.
Class - A class can be defined as a template/blueprint that describes the behaviors/states that object of its type support.
Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
Instant Variables - Each object has its unique set of instant variables. An object's state is created by the values assigned to these instant variables.
C++ Program Structure:
Let us look at a simple code that would print the words Hello World.
#include <iostream>
using namespace std;
// main() is where program execution begins.
int main()
{
cout << "Hello World"; // prints Hello World
return 0;
}
Let us look various parts of the above program:
The C++ language defines several headers, which contain information that is either necessary or useful to your program. For this program, the header <iostream> is needed.
The line using namespace std; tells the compiler to use the std namespace. Namespaces are a relatively recent addition to C++.
The next line // main() is where program execution begins. is a single-line comment available in C++. Single-line comments begin with // and stop at the end of the line.
The line int main() is the main function where program execution begins.
The next line cout << "This is my first C++ program."; causes the message "This is my first C++ program" to be displayed on the screen.
The next line return 0; terminates main( )function and causes it to return the value 0 to the calling process.
Compile & Execute C++ Program:
Let's look at how to save the file, compile and run the program. Please follow the steps given below:
Open a text editor and add the code as above.
Save the file as: hello.cpp
Open a command prompt and go to the directory where you saved the file.
Type 'g++ hello.cpp ' and press enter to compile your code. If there are no errors in your code the command prompt will take you to the next line and would generate a.out executable file.
Now, type ' a.out' to run your program.
You will be able to see ' Hello World ' printed on the window.
$ g++ hello.cpp
$ ./a.out
Hello World
Make sure that g++ is in your path and that you are running it in the directory containing file hello.cpp.
Semicolons & Blocks in C++:
In C++, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.
For example, following are three different statements:
x = y;
y = y+1;
add(x, y);
A block is a set of logically connected statements that are surrounded by opening and closing braces. For example:
{
cout << "Hello World"; // prints Hello World
return 0;
}
C++ does not recognize the end of the line as a terminator. For this reason, it does not matter where on a line you put a statement. For example:
x = y;
y = y+1;
add(x, y);
C++ Identifiers:
A C++ identifier is a name used to identify a variable, function, class, module, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore (_) followed by zero or more letters, underscores, and digits (0 to 9).
C++ does not allow punctuation characters such as @, $, and % within identifiers. C++ is a case-sensitive programming language. Thus, Manpower and manpower are two different identifiers in C++.
C++ Keywords:
The following list shows the reserved words in C++. These reserved words may not be used as constant or variable or any other identifier names.
| asm |
else |
new |
this |
| auto |
enum |
operator |
throw |
| bool |
explicit |
private |
true |
| break |
export |
protected |
try |
| case |
extern |
public |
typedef |
| catch |
false |
register |
typeid |
| char |
float |
reinterpret_cast |
typename |
| class |
for |
return |
union |
| const |
friend |
short |
unsigned |
| const_cast |
goto |
signed |
using |
| continue |
if |
sizeof |
virtual |
| default |
inline |
static |
void |
| delete |
int |
static_cast |
volatile |
| do |
long |
struct |
wchar_t |
| double |
mutable |
switch |
while |
| dynamic_cast |
namespace |
template |
|
Trigraphs:
A few characters have an alternative representation, called a trigraph sequence. A trigraph is a three-character sequence that represents a single character and the sequence always starts with two question marks.
Trigraphs are expanded anywhere they appear, including within string literals and character literals, in comments, and in preprocessor directives.
Following are most frequently used trigraph sequences:
| Trigraph |
Replacement |
| ??= |
# |
| ??/ |
\ |
| ??' |
^ |
| ??( |
[ |
| ??) |
] |
| ??! |
| |
| ??< |
{ |
| ??> |
} |
| ??- |
~ |
