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Your first program

Learn to write your first C++ program with main, #include and iostream.

Your first program

The entry point of every C++ program is the main function. When the program starts, main is called and runs until return 0;.

To write a program you first include the standard I/O library with #include <iostream>. std::cout prints text to the screen; std::endl ends the line and moves the cursor to the next line.

From the command line you compile with g++ hello.cpp -o hello and run with ./hello. C++ source files usually use the .cpp extension.

What is #include?

#include is a preprocessor directive: before compiling, the compiler pastes the named header file into your source. <iostream> provides std::cout and std::cin for input and output.

Header names go inside <...> and are not followed by a semicolon. Standard library headers do not use a .h extension; for your own headers you write #include "mine.hpp" with quotes.

A program can have several #include lines; each one must be on its own line.

Practice Write your first program

Complete the skeleton below. Inside main, use std::cout to print Hello World and end the line with std::endl.

Starter code

main.cpp
#include <iostream>

int main() {
    // Print the message
    return 0;
}

Sample solution

main.cpp
#include <iostream>

int main() {
    // Print the message
    std::cout << "Hello World" << std::endl;
    return 0;
}

Expected output

Hello World

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What is the entry point of a C++ program?

  • the start function
  • the main function Correct answer
  • the run function
  • the init function

Explanation: The main function is the entry point of a C++ program.

2 The #include line

Question 
#include <____> to include the input/output library.
Answer 
#include <iostream> to include the input/output library.

Explanation: iostream provides std::cout and std::cin.

3 Match the program parts

Term Meaning
int main() Entry point
return 0; Successful exit
std::cout Output writing
#include Library inclusion

All lessons in Beginner

1 C++ basics

  1. What is C++?
  2. Your first program
  3. std::cout
  4. std::cin
  5. Comments
  6. Summary - C++ basics

2 Variables

  1. Declaring variables
  2. auto
  3. const
  4. constexpr
  5. Type conversion
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and char
  4. std::string
  5. sizeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 Strings

  1. std::string basics
  2. String concatenation
  3. String length
  4. Substring
  5. String search
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range-based for
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. C-style arrays
  2. Array access
  3. std::array
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 std::vector

  1. Declaring vectors
  2. push_back
  3. size and at
  4. Vector access
  5. Vector loop
  6. Summary - std::vector

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function overloading
  5. Default parameters
  6. Summary - Functions

13 References

  1. What is a reference?
  2. Declaring references
  3. Reference parameters
  4. const references
  5. Dangling references
  6. Summary - References

14 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. nullptr
  5. Pointer arithmetic
  6. Summary - Pointer basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. String streams
  2. stoi and stod
  3. to_string
  4. String comparison
  5. String modification
  6. Summary - Advanced strings

17 Structs

  1. Defining structs
  2. Using structs
  3. Struct and function
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Exception basics

  1. try/catch
  2. throw
  3. std::exception
  4. Custom exceptions
  5. catch all
  6. Summary - Exceptions

19 Namespaces

  1. Defining namespaces
  2. using
  3. std namespace
  4. Nested namespaces
  5. Namespace alias
  6. Summary - Namespaces

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together