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Basic Syntax in C++

Program Structure

C++ programs run line by line and generally follow the same program structure:

  • #include statements at the beginning of the program, which allow access to library functionalities.
  • main() function, which is run when the program is executed.
  • return 0 at the end of the main() function, which indicates that the program ran without issues.
#include <iostream> using namespace std; int main() { cout << "Hello, world!"; return 0; }


Comments are notes left by the programmer that explain complex code. Comments do not affect the performance of a program because they are ignored by the compiler.

In C++, there are two types of comments:

  • Single-line: begin with //.
  • Multi-line: begin with /* and end with */.

As a rule of thumb, comments should always go above the code they are commenting on.

// I am a single-line comment /* I am a multi-line comment */

Input and Output

Input and output make C++ programs more interactive.

  • #include <iostream> must be placed at the beginning of the program to access input and output.
  • std::cout is the “character output” and it is used together with << to print to the terminal.
  • std::cin is the “character input” and it is used together with >> to read user input.
  • std::endl or \n can be used to insert a new line.
#include <iostream> int main() { int age; std::cout << "How old are you? "; std::cin >> age; std::cout << "You are " << age << " years old."; return 0; }


Variables are used to store and retrieve data. When declaring a variable, it must be given a data type and a name.

Multiple variables of the same type can be declared in a single statement using a comma-separated list.

Variables can be declared with the const keyword, which prevents their value from being changed later.

int number = 100; char letter; letter = 'c'; const int pi = 3.14;

References and Pointers

C++ provides two powerful features for memory manipulation:

  • References: aliases to existing variables
  • Pointers: store memory address as its value

Reference variables are created using the & symbol. & is also used to access the memory address of a variable.

Pointer variables are created using the * symbol. * is also used to obtain the value pointed to by a pointer variable.

int year = 2021; int &ref = year; int *ptr = &year; std::cout << &year << "\n"; std::cout << *ptr << "\n";


A variable refers to a storage location in the computer’s memory that one can set aside to save, retrieve, and manipulate data.

// Declare a variable int score; // Initialize a variable score = 0;

double Type

double is a type for storing floating point (decimal) numbers. Double variables typically require 8 bytes of memory space.

double price = 8.99; double pi = 3.14159;

Arithmetic Operators

C++ supports different types of arithmetic operators that can perform common mathematical operations:

  • + addition
  • - subtraction
  • * multiplication
  • / division
  • % modulo (yields the remainder)
int x = 0; x = 4 + 2; // x is now 6 x = 4 - 2; // x is now 2 x = 4 * 2; // x is now 8 x = 4 / 2; // x is now 2 x = 4 % 2; // x is now 0

User Input

std::cin, which stands for “character input”, reads user input from the keyboard.

Here, the user can enter a number, press enter, and that number will get stored in tip.

int tip = 0; std::cout << "Enter amount: "; std::cin >> tip;

Chaining the Output

std::cout can output multiple values by chaining them using the output operator <<.

Here, the output would be I'm 28.

int age = 28; std::cout << "I'm " << age << ".\n";

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