C++ Basic Syntax

Syntax refers to the rules and regulations for writing statements in a programming language. They can also be viewed as the grammatical rules defining the structure of a programming language.

The C++ language also has its syntax for the functionalities it provides. Different statements have different syntax specifying their usage, but C++ programs also have basic syntax rules that are followed throughout all the programs.

Basic Syntax of a C++ Program

We can learn about basic C++ Syntax using the following program.

// C++ program to demonstrate the basic syntax
// Header File Library
#include <iostream>

// Standard Namespace
using namespace std;

// Main Function
int main()
{

    // Body of the Function

    // Declaration of Variable
    int num1 = 24;
    int num2 = 34;

    int result = num1 + num2;

    // Output
    cout << result << endl;

    // Return Statement
    return 0;
}

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The program above shows the basic C++ program that contains header files, main function, namespace declaration, etc. Let's try to understand them one by one.

1. Header File

The header files contain the definition of the functions and macros we are using in our program. In line #1, we used the #include  <iostream> statement to tell the compiler to include an iostream header file library which stores the definition of the cin and cout standard input/output streams that we have used for input and output. #include is a preprocessor directive using which we import header files.

2. Namespace

A namespace in C++ is used to provide a scope or a region where we define identifiers. In line #2, we have used the using namespace std statement for specifying that we will be the standard namespace where all the standard library functions are defined.

3. Main Function

In line #3, we defined the main function as int main(). The main function is the most important part of any C++ program. The program execution always starts from the main function. All the other functions are called from the main function. In C++, the main function is required to return some value indicating the execution status.

4. Blocks

Blocks are the group of statements that are enclosed within { } braces. The body of the main function is from line #4 to line #9 enclosed within  { }.

5. Semicolons

As you may have noticed by now, each statement in the above code is followed by a ( ; ) semicolon symbol. It is used to terminate each line of the statement of the program.

6. Identifiers

We use identifiers for the naming of variables, functions, and other user-defined data types. An identifier may consist of uppercase and lowercase alphabetical characters, underscore, and digits. The first letter must be an underscore or an alphabet.

7. Keywords

In the C++ programming language, there are some reserved words that are used for some special meaning in the C++ program. It can't be used for identifiers. For example, the words int, return, and using are some keywords used in our program.

8. Basic Output cout

In line #7, we have used the cout stream object (declared in the <iostream> header file) to print the sum of two numbers to the standard output stream (stdout).

Object-Oriented Programming in C++

C++ programming language supports both procedural-oriented and object-oriented programming. The above example is based on the procedural-oriented programming paradigm. So let's take another example to discuss Object Oriented Programming in C++.

#include <iostream>
using namespace std;

class Calculate {

	// Access Modifiers
public:

	// data member
	int num1 = 50;
	int num2 = 30;

	// member function
	void addition() {
		int result = num1 + num2;
		cout << result << endl;
	}
};

int main() {

	// object declaration
	Calculate add;
	
	// member function calling
	add.addition();

	return 0;
}

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1. Class

A class is a user-defined data type. A class has its own attributes (data members) and behavior (member functions). In line #3, we have declared a class named Calculate and its body expands from line #3 to line #7.

2. Data Members & Member Functions

The attributes or data in the class are defined by the data members & the functions that work on these data members are called the member functions.

In the above example, num1 and num2 are the data member & addition() is a member function that is working on these two data members. There is a keyword here public that is access modifiers. The access modifier decides who has access to these data members & member functions.

3. Object

The object is an instance of a class. The class itself is just a template that is not allocated any memory. To use the data and methods defined in the class, we have to create an object of that class.