Chapter 3: Your First C++ Program

Now that you have installed a C++ development environment, it's time to write your first C++ program.

Traditionally, every programmer begins with the Hello, World! program. Although it is simple, it introduces the basic structure of every C++ application.

Hello, World! Program

Create a new file named hello.cpp and write the following code:

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << "Hello, World!" << endl;
8
9    return 0;
10}

Output

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1Hello, World!

This program displays the text Hello, World! on the screen.

Understanding the Program

Let's examine each line in detail.

1. Header Files

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1#include <iostream>

The #include directive tells the compiler to include another file before compilation.

<iostream> is a header file that provides functionality for input and output operations.

Without including this header, objects such as cout, cin, and endl are unavailable.

Why is it needed?

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1#include <iostream>
2
3int main()
4{
5    std::cout << "Hello";
6}

Without <iostream>, the compiler will report an error because it doesn't know what std::cout is.

Common C++ Header Files

2. using namespace std;

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1using namespace std;

The C++ Standard Library places its features inside the std namespace.

Instead of writing:

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1std::cout << "Hello";

you can write:

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1cout << "Hello";

because of:

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1using namespace std;

Without using namespace std

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1#include <iostream>
2
3int main()
4{
5    std::cout << "Hello, World!";
6    return 0;
7}

With using namespace std

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << "Hello, World!";
8    return 0;
9}

Best Practice: In large projects, prefer using std::cout instead of using namespace std; to avoid naming conflicts.

3. The main() Function

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1int main()
2{
3}

Every C++ program starts execution from the main() function.

It is the entry point of the application.

The operating system calls this function when the program begins.

Syntax

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1int main()
2{
3    // Program statements
4}

Program Flow

Program Starts
       │
       ▼
main()
       │
       ▼
Statements Execute
       │
       ▼
Program Ends

Only one main() function is allowed in a C++ program.

4. Curly Braces { }

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1int main()
2{
3    // Statements
4}

Curly braces define a block of code.

Everything between { and } belongs to the main() function.

Example:

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1int main()
2{
3    int age = 20;
4
5    cout << age;
6
7    return 0;
8}

5. cout

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1cout << "Hello, World!";

cout stands for Character Output.

It is used to display output on the console.

Syntax

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1cout << value;

Example

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1cout << "Welcome";

Output

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1Welcome

Printing Numbers

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1cout << 100;

Output

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1100

Printing Variables

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1int age = 22;
2
3cout << age;

Output

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122

Printing Multiple Values

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1string name = "Ankit";
2int age = 23;
3
4cout << name << " " << age;

Output

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1Ankit 23

The << operator is called the stream insertion operator.

It sends data to the output stream.

6. endl

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1cout << "Hello" << endl;

endl inserts a new line and flushes the output buffer.

Example:

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1cout << "One" << endl;
2cout << "Two";

Output

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1One
2Two

You can also use the newline character:

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1cout << "One\n";
2cout << "Two";

Output

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1One
2Two

endl vs \n

For most applications, \n is preferred for better performance unless you specifically need to flush the output.

7. return 0;

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1return 0;

The return statement ends the main() function and returns a value to the operating system.

A return value of 0 indicates that the program executed successfully.

Example

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1int main()
2{
3    cout << "Done";
4
5    return 0;
6}

Output

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1Done

Return Codes

Complete Program Flow

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << "Hello, World!" << endl;
8
9    return 0;
10}

Execution order:

1. The compiler includes the iostream header.
2. The operating system calls main().
3. cout prints Hello, World!.
4. endl moves the cursor to the next line.
5. return 0 ends the program successfully.

Common Beginner Mistakes

Missing Semicolon

Incorrect:

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1cout << "Hello"

Correct:

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1cout << "Hello";

Missing Header File

Incorrect:

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1int main()
2{
3    cout << "Hello";
4}

Correct:

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << "Hello";
8}

Misspelling main

Incorrect:

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1int Main()
2{
3}

Correct:

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1int main()
2{
3}

Missing return

Although modern C++ allows omitting return 0; in main(), explicitly including it improves readability.

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1int main()
2{
3    cout << "Hello";
4
5    return 0;
6}

Practice Exercises

Exercise 1

Print your name.

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << "Ankit";
8
9    return 0;
10}

Exercise 2

Print two lines.

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << "Welcome to C++" << endl;
8    cout << "Happy Coding!";
9
10    return 0;
11}

Exercise 3

Print your age.

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << "Age: 23";
8
9    return 0;
10}

Summary

In this chapter, you learned:

• How to write your first C++ program.
• The purpose of the #include directive and header files.
• Why using namespace std; is used.
• The role of the main() function as the program's entry point.
• How cout displays output to the console.
• The difference between endl and \n.
• Why return 0; signals successful program execution.
• Common beginner mistakes and how to avoid them.

With this foundation, you're ready to explore variables, data types, input/output, and other core C++ concepts in the next chapter.