C++ Tutorial
Learn C++
C++ is a popular programming language.
C++ is used to create computer programs and is one of the most used languages in game development.
Examples in Each Chapter
Our "Try it Yourself" editor makes it easy to learn C++. You can edit C++ code and view the result in your browser.
Example
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!";
return 0;
}
We recommend reading this tutorial, in the sequence listed in the left menu.
C++ is an object-oriented language and some concepts may be new. Take breaks when needed, and go over the examples as many times as needed.
C++ Introduction
What is C++?
C++ is a cross-platform language that can be used to create high-performance applications.
C++ was developed by Bjarne Stroustrup, as an extension to the C language.
C++ gives programmers a high level of control over system resources and memory.
The language was updated 4 major times in 2011, 2014, 2017, and 2020 to C++11, C++14, C++17, and C++20.
Why Use C++
C++ is one of the world's most popular programming languages.
C++ can be found in today's operating systems, Graphical User Interfaces, and embedded systems.
C++ is an object-oriented programming language that gives a clear structure to programs and allows code to be reused, lowering development costs.
C++ is portable and can be used to develop applications that can be adapted to multiple platforms.
C++ is fun and easy to learn!
As C++ is close to C, C#, and Java, it makes it easy for programmers to switch to C++ or vice versa.
Difference between C and C++
C++ was developed as an extension of C, and both languages have almost the same syntax.
The main difference between C and C++ is that C++ supports classes and objects, while C does not.
C++ Getting Started
C++ Get Started
To start using C++, you need two things:
A text editor, like Notepad, to write C++ code
A compiler, like GCC, to translates the C++ code into a language that the computer will understand
There are many text editors and compilers to choose from. In this tutorial, we will use an IDE (see below).
C++ Install IDE
An IDE (Integrated Development Environment) is used to edit AND compile the code.
Popular IDE's include Code::Blocks, Eclipse, and Visual Studio. These are all free, and they can be used to both edit and debug C++ code.
Note: Web-based IDE's can work as well, but functionality is limited.
We will use Code::Blocks in our tutorial, which we believe is a good place to start.
You can find the latest version of Codeblocks at http://www.codeblocks.org/. Download the mingw-setup.exe file, which will install the text editor with a compiler.
C++ Quickstart
Let's create our first C++ file.
Open Codeblocks and go to File > New > Empty File.
Write the following C++ code and save the file as myfirstprogram.cpp (File > Save File as):
myfirstprogram.cpp
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!";
return 0;
}
Don't worry if you don't understand the code above - we will discuss it in detail in later chapters. For now, focus on how to run the code.
In Codeblocks, it should look like this:
Then, go to Build > Build and Run to run (execute) the program. The result will look something to this:
Result:
Hello World!
Process returned 0 (0x0) execution time : 0.011 s
Press any key to continue.
Congratulations! You have now written and executed your first C++ program.
Learning C++ At W3Schools
When learning C++ at W3Schools.com, you can use our "Try it Yourself" tool, which shows both the code and the result. This will make it easier for you to understand every part as we move forward:
myfirstprogram.cpp
Code:
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!";
return 0;
}
Result:
Hello World!
C++ Syntax
Let's break up the following code to understand it better:
Example
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!";
return 0;
}
Example explained
Line 1: #include <iostream> is a header file library that lets us work with input and output objects, such as cout (used in line 5). Header files add functionality to C++ programs.
Line 2: using namespace std means that we can use names for objects and variables from the standard library.
Don't worry if you don't understand how #include <iostream> and using namespace std works. Just think of it as something that (almost) always appears in your program.
Line 3: A blank line. C++ ignores white space. But we use it to make the code more readable.
Line 4: Another thing that always appears in a C++ program, is int main(). This is called a function. Any code inside its curly brackets {} will be executed.
Line 5: cout (pronounced "see-out") is an object used together with the insertion operator (<<) to output/print text. In our example it will output "Hello World".
Note: Every C++ statement ends with a semicolon ;
Note: The body of int main() could also be written as:
int main () { cout << "Hello World! "; return 0; }
Remember: The compiler ignores white spaces. However, multiple lines make the code more readable.
Line 6: return 0 ends the main function.
Line 7: Do not forget to add the closing curly bracket } to actually end the main function.
Omitting Namespace
You might see some C++ programs that rus without the standard namespace library. The using namespace std line can be omitted and replaced with the std keyword, followed by the: operator for some objects:
Example
#include <iostream>
int main() {
std::cout << "Hello World!";
return 0;
}
It is up to you if you want to include the standard namespace library or not.
C++ Output (Print Text)
The cout object, together with the << operator, is used to output values/print text:
Example
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!";
return 0;
}
You can add as many cout objects as you want. However, note that it does not insert a new line at the end of the output:
Example
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!";
cout << "I am learning C++";
return 0;
}
C++ New Lines
New Lines
To insert a new line, you can use the \n character:
Example
#include <iostream>
using namespace std;
int main() {
cout << "Hello World! \n";
cout << "I am learning C++";
return 0;
}
Tip: Two \n characters after each other will create a blank line:
Example
#include <iostream>
using namespace std;
int main() {
cout << "Hello World! \n\n";
cout << "I am learning C++";
return 0;
}
Another way to insert a new line is with the end l manipulator:
Example
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!" << endl;
cout << "I am learning C++";
return 0;
}
Both \n and end l are used to break lines. However, \n is the most used.
But what is \n exactly?
The newline character (\n) is called an escape sequence, and it forces the cursor to change its position to the beginning of the next line on the screen. This results in a new line.
Examples of other valid escape sequences are:
Escape Sequence DescriptionTry it
\t Creates a horizontal tab
\\ Inserts a backslash character (\)
\" Inserts a double quote character
C++ Comments
Comments can be used to explain C++ code, and to make it more readable. It can also be used to prevent execution when testing alternative code. Comments can be singled-lined or multi-lined.
Single-line Comments
Single-line comments start with two forward slashes (//).
Any text between // and the end of the line is ignored by the compiler (will not be executed).
This example uses a single-line comment before a line of code:
Example
// This is a comment
cout << "Hello World!";
This example uses a single-line comment at the end of a line of code:
Example
cout << "Hello World!"; // This is a comment
C++ Multi-line Comments
Multi-line comments start with /* and ends with */.
Any text between /* and */ will be ignored by the compiler:
Example
/* The code below will print the words Hello World!
to the screen, and it is amazing */
cout << "Hello World!";
Single or multi-line comments?
It is up to you which you want to use. Normally, we use // for short comments, and /* */ for longer.
C++ Variables
Variables are containers for storing data values.
In C++, there are different types of variables (defined with different keywords), for example:
int - stores integers (whole numbers), without decimals, such as 123 or -123
double - stores floating point numbers, with decimals, such as 19.99 or -19.99
char - stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotes
string - stores text, such as "Hello World". String values are surrounded by double quotes
bool - stores values with two states: true or false
Declaring (Creating) Variables
To create a variable, specify the type and assign it a value:
Syntax
type variableName = value;
Where type is one of C++ types (such as int), and variableName is the name of the variable (such as x or myName). The equal sign is used to assign values to the variable.
To create a variable that should store a number, look at the following example:
Example
Create a variable called myNum of type int and assign it the value 15:
int myNum = 15;
cout << myNum;
You can also declare a variable without assigning the value, and assign the value later:
Example
int myNum;
myNum = 15;
cout << myNum;
Note that if you assign a new value to an existing variable, it will overwrite the previous value:
Example
int myNum = 15; // myNum is 15
myNum = 10; // Now myNum is 10
cout << myNum; // Outputs 10
Other Types
A demonstration of other data types:
Example
int myNum = 5; // Integer (whole number without decimals)
double myFloatNum = 5.99; // Floating point number (with decimals)
char myLetter = 'D'; // Character
string myText = "Hello"; // String (text)
bool myBoolean = true; // Boolean (true or false)
You will learn more about the individual types in the Data Types chapter.
Display Variables
The cout object is used together with the << operator to display variables.
To combine both text and a variable, separate them with the << operator:
Example
int myAge = 35;
cout << "I am " << myAge << " years old.";
Add Variables Together
To add a variable to another variable, you can use the + operator:
Example
int x = 5;
int y = 6;
int sum = x + y;
cout << sum;
C++ Declare Multiple Variables
Declare Many Variables
To declare more than one variable of the same type, use a comma-separated list:
Example
int x = 5, y = 6, z = 50;
cout << x + y + z;
One Value to Multiple Variables
You can also assign the same value to multiple variables in one line:
Example
int x, y, z;
x = y = z = 50;
cout << x + y + z;
C++ Identifiers
All C++ variables must be identified with unique names.
These unique names are called identifiers.
Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).
Note: It is recommended to use descriptive names in order to create understandable and maintainable code:
Example
// Good
int minutesPerHour = 60;
// OK, but not so easy to understand what m actually is
int m = 60;
The general rules for naming variables are:
- Names can contain letters, digits and underscores
- Names must begin with a letter or an underscore (_)
- Names are case sensitive (myVar and myvar are different variables)
- Names cannot contain whitespaces or special characters like !, #, %, etc.
- Reserved words (like C++ keywords, such as int) cannot be used as names
C++ Constants
Constants
When you do not want others (or yourself) to change existing variable values, use the const keyword (this will declare the variable as "constant", which means unchangeable and read-only):
Example
const int myNum = 15; // myNum will always be 15
myNum = 10; // error: assignment of read-only variable 'myNum'
You should always declare the variable as constant when you have values that are unlikely to change:
Example
const int minutesPerHour = 60;
const float PI = 3.14;
C++ User Input
You have already learned that cout is used to output (print) values. Now we will use cin to get user input.
cin is a predefined variable that reads data from the keyboard with the extraction operator (>>).
In the following example, the user can input a number, which is stored in the variable x. Then we print the value of x:
Example
int x;
cout << "Type a number: "; // Type a number and press enter
cin >> x; // Get user input from the keyboard
cout << "Your number is: " << x; // Display the input value
Good To Know
cout is pronounced "see-out". Used for output, and uses the insertion operator (<<)
cin is pronounced "see-in". Used for input, and uses the extraction operator (>>)
Creating a Simple Calculator
In this example, the user must input two numbers. Then we print the sum by calculating (adding) the two numbers:
Example
int x, y;
int sum;
cout << "Type a number: ";
cin >> x;
cout << "Type another number: ";
cin >> y;
sum = x + y;
cout << "Sum is: " << sum;
There you go! You just built a basic calculator!
C++ Exercises
Test Yourself With Exercises
Exercise:
Use the correct keyword to get user input, stored in the variable x:
int x;
cout << "Type a number: ";
>>
;
C++ Data Types
C++ Data Types
As explained in the Variables chapter, a variable in C++ must be a specified data type:
Example
int myNum = 5; // Integer (whole number)
float myFloatNum = 5.99; // Floating point number
double myDoubleNum = 9.98; // Floating point number
char myLetter = 'D'; // Character
bool myBoolean = true; // Boolean
string myText = "Hello"; // String
Basic Data Types
The data type specifies the size and type of information the variable will store:
Data Type Size Description
boolean 1 byte Stores true or false values
char 1 byte Stores a single character/letter/number, or ASCII values
int 2 or 4 bytes Stores whole numbers, without decimals
float 4 bytes Stores fractional numbers, containing one or more decimals. Sufficient for storing 6-7 decimal digits
double 8 bytes Stores fractional numbers, containing one or more decimals. Sufficient for storing 15 decimal digits
You will learn more about the individual data types in the next chapters.
C++ Exercises
Test Yourself With Exercises
Exercise:
Add the correct data type for the following variables:
myNum = 9;
myDoubleNum = 8.99;
myLetter = 'A';
myBool = false;
myText = "Hello World";
C++ Numeric Data Types
Numeric Types
Use int when you need to store a whole number without decimals, like 35 or 1000, and float or double when you need a floating point number (with decimals), like 9.99 or 3.14515.
int
int myNum = 1000;
cout << myNum;
float
float myNum = 5.75;
cout << myNum;
double
double myNum = 19.99;
cout << myNum;
float vs. double
The precision of a floating point value indicates how many digits the value can have after the decimal point. The precision of float is only six or seven decimal digits, while double variables have a precision of about 15 digits. Therefore it is safer to use double for most calculations.
Scientific Numbers
A floating point number can also be a scientific number with an "e" to indicate the power of 10:
Example
float f1 = 35e3;
double d1 = 12E4;
cout << f1;
cout << d1;
C++ Boolean Data Types
Boolean Types
A boolean data type is declared with the bool keyword and can only take the values true or false.
When the value is returned, true = 1 and false = 0.
Example
bool isCodingFun = true;
bool isFishTasty = false;
cout << isCodingFun; // Outputs 1 (true)
cout << isFishTasty; // Outputs 0 (false)
C++ Character Data Types
Character Types
The char data type is used to store a single character. The character must be surrounded by single quotes, like 'A' or 'c':
Example
char myGrade = 'B';
cout << myGrade;
Alternatively, you can use ASCII values to display certain characters:
Example
char a = 65, b = 66, c = 67;
cout << a;
cout << b;
cout << c;
C++ String Data Types
String Types
The string type is used to store a sequence of characters (text). This is not a built-in type, but it behaves like one in its most basic usage. String values must be surrounded by double quotes:
Example
string greeting = "Hello";
cout << greeting;
To use strings, you must include an additional header file in the source code, the <string> library:
Example
// Include the string library
#include <string>
// Create a string variable
string greeting = "Hello";
// Output string value
cout << greeting;
C++ Operators
Operators are used to performing operations on variables and values.
In the example below, we use the + operator to add together two values:
Example
int x = 100 + 50;
Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:
Example
int sum1 = 100 + 50; // 150 (100 + 50)
int sum2 = sum1 + 250; // 400 (150 + 250)
int sum3 = sum2 + sum2; // 800 (400 + 400)
C++ divides the operators into the following groups:
Arithmetic operators
Assignment operators
Comparison operators
Logical operators
Bitwise operators
Arithmetic Operators
Arithmetic operators are used to performing common mathematical operations.
Operator Name Description Example
+ Addition Adds together two values x + y
- Subtraction Subtracts one value from another x - y
* Multiplication Multiplies two values x * y
/ Division Divides one value by another x / y
% Modulus Returns the division remainder x % y
++ Increment Increases the value of a variable by 1 ++x
-- Decrement Decreases the value of a variable by 1 --x
C++ Exercises
Test Yourself With Exercises
Exercise:
Multiply 10 with 5, and print the result.
cout << 10 5;
C++ Assignment Operators
Assignment Operators
Assignment operators are used to assignimg values to variables.
In the example below, we use the assignment operator (=) to assign the value 10 to a variable called x:
Example
int x = 10;
The addition assignment operator (+=) adds a value to a variable:
Example
int x = 10;
x += 5;
A list of all assignment operators:
Operator Example Same As
= x = 5 x = 5
+= x += 3 x = x + 3
-= x -= 3 x = x - 3
*= x *= 3 x = x * 3
/= x /= 3 x = x / 3
%= x %= 3 x = x % 3
&= x &= 3 x = x & 3
|= x |= 3 x = x | 3
^= x ^= 3 x = x ^ 3
>>= x >>= 3 x = x >> 3
<<= x <<= 3 x = x << 3
C++ Comparison Operators
Comparison operators are used to comparing two values (or variables). This is important in programming because it helps us to find answers and make decisions.
The return value of a comparison is either 1 or 0, which means true (1) or false (0). These values are known as Boolean values, and you will learn more about them in the Booleans and If...Else chapter.
In the following example, we use the greater than operator (>) to find out if 5 is greater than 3:
Example
int x = 5;
int y = 3;
cout << (x > y); // returns 1 (true) because 5 is greater than 3
A list of all comparison operators:
Operator Name Example
== Equal to x == y
!= Not equal x != y
> Greater than x > y
< Less than x < y
>= Greater than or equal to x >= y
<= Less than or equal to x <= y
C++ Logical Operators
Logical Operators
As with comparison operators, you can also test for true (1) or false (0) values with logical operators.
C++ Strings
Strings are used for storing text.
A string variable contains a collection of characters surrounded by double quotes:
Example
Create a variable of type string and assign it a value:
string greeting = "Hello";
To use strings, you must include an additional header file in the source code, the <string> library:
Example
// Include the string library
#include <string>
// Create a string variable
string greeting = "Hello";
String Concatenation
The + operator can be used between strings to add them together to make a new string. This is called concatenation:
Example
string firstName = "John ";
string lastName = "Doe";
string fullName = firstName + lastName;
cout << fullName;
In the example above, we added a space after firstName to create a space between John and Doe on output. However, you could also add a space with quotes (" " or ' '):
Example
string firstName = "John";
string lastName = "Doe";
string fullName = firstName + " " + lastName;
cout << fullName;
Append
A string in C++ is actually an object, which contains functions that can perform certain operations on strings. For example, you can also concatenate strings with the append() function:
Example
string firstName = "John ";
string lastName = "Doe";
string fullName = firstName.append(lastName);
cout << fullName;
C++ Numbers and Strings
Adding Numbers and Strings
WARNING!
C++ uses the + operator for both addition and concatenation.
Numbers are added. Strings are concatenated.
If you add two numbers, the result will be a number:
Example
int x = 10;
int y = 20;
int z = x + y; // z will be 30 (an integer)
If you add two strings, the result will be a string concatenation:
Example
string x = "10";
string y = "20";
string z = x + y; // z will be 1020 (a string)
If you try to add a number to a string, an error occurs:
Example
string x = "10";
int y = 20;
string z = x + y;
C++ String Length
String Length
To get the length of a string, use the length() function:
Example
string txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
cout << "The length of the txt string is: " << txt.length();
Tip: You might see some C++ programs that use the size() function to get the length of a string. This is just an alias of length(). It is completely up to you if you want to use length() or size():
Example
string txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
cout << "The length of the txt string is: " << txt.size();
C++ Access Strings
Access Strings
You can access the characters in a string by referring to its index number inside square brackets [].
This example prints the first character in myString:
Example
string myString = "Hello";
cout << myString[0];
// Outputs H
Note: String indexes start with 0: [0] is the first character. [1] is the second character, etc.
This example prints the second character in myString:
Example
string myString = "Hello";
cout << myString[1];
// Outputs e
Change String Characters
To change the value of a specific character in a string, refer to the index number, and use single quotes:
Example
string myString = "Hello";
myString[0] = 'J';
cout << myString;
// Outputs Jello instead of Hello
C++ Special Characters
Strings - Special Characters
Because strings must be written within quotes, C++ will misunderstand this string, and generate an error:
string txt = "We are the so-called "Vikings" from the north.";
The solution to avoid this problem, is to use the backslash escape character.
The backslash (\) escape character turns special characters into string characters:
Escape character Result Description
\' ' Single quote
\" " Double quote
\\ \ Backslash
The sequence \" inserts a double quote in a string:
Example
string txt = "We are the so-called \"Vikings\" from the north.";
The sequence \' inserts a single quote in a string:
Example
string txt = "It\'s alright.";
The sequence \\ inserts a single backslash in a string:
Example
string txt = "The character \\ is called backslash.";
Other popular escape characters in C++ are:
Escape Character Result
\n New Line
\t Tab
C++ User Input Strings
User Input Strings
It is possible to use the extraction operator >> on cin to display a string entered by a user:
Example
string firstName;
cout << "Type your first name: ";
cin >> firstName; // get user input from the keyboard
cout << "Your name is: " << firstName;
// Type your first name: John
// Your name is: John
However, cin considers a space (whitespace, tabs, etc) as a terminating character, which means that it can only display a single word (even if you type many words):
Example
string fullName;
cout << "Type your full name: ";
cin >> fullName;
cout << "Your name is: " << fullName;
// Type your full name: John Doe
// Your name is: John
From the example above, you would expect the program to print "John Doe", but it only prints "John".
That's why, when working with strings, we often use the getline() function to read a line of text. It takes cin as the first parameter and the string variable as the second:
Example
string fullName;
cout << "Type your full name: ";
getline (cin, fullName);
cout << "Your name is: " << fullName;
// Type your full name: John Doe
// Your name is: John Doe
C++ String Namespace
Omitting Namespace
You might see some C++ programs that run without the standard namespace library. The using namespace std line can be omitted and replaced with the std keyword, followed by the :: operator for string (and cout) objects:
Example
#include <iostream>
#include <string>
int main() {
std::string greeting = "Hello";
std::cout << greeting;
return 0;
}
It is up to you if you want to include the standard namespace library or not.
C++ Math
C++ has many functions that allows you to perform mathematical tasks on numbers.
Max and min
The max(x,y) function can be used to find the highest value of x and y:
Example
cout << max(5, 10);
And the min(x,y) function can be used to find the lowest value of x and y:
Example
cout << min(5, 10);
C++ <cmath> Header
Other functions, such as sqrt (square root), round (rounds a number) and log (natural logarithm), can be found in the <cmath> header file:
Example
// Include the cmath library
#include <cmath>
cout << sqrt(64);
cout << round(2.6);
cout << log(2);
C++ Booleans
Very often, in programming, you will need a data type that can only have one of two values, like:
YES / NO
ON / OFF
TRUE / FALSE
For this, C++ has a bool data type, which can take the values true (1) or false (0).
Boolean Values
A boolean variable is declared with the bool keyword and can only take the values true or false:
Example
bool isCodingFun = true;
bool isFishTasty = false;
cout << isCodingFun; // Outputs 1 (true)
cout << isFishTasty; // Outputs 0 (false)
From the example above, you can read that a true value returns 1, and false returns 0.
However, it is more common to return a boolean value by comparing values and variables (see next page).
C++ Boolean Expressions
Boolean Expression
A Boolean expression returns a boolean value that is either 1 (true) or 0 (false).
This is useful to build logic, and find answers.
You can use a comparison operator, such as the greater than (>) operator, to find out if an expression (or variable) is true or false:
Example
int x = 10;
int y = 9;
cout << (x > y); // returns 1 (true), because 10 is higher than 9
Or even easier:
Example
cout << (10 > 9); // returns 1 (true), because 10 is higher than 9
In the examples below, we use the equal to (==) operator to evaluate an expression:
Example
int x = 10;
cout << (x == 10); // returns 1 (true), because the value of x is equal to 10
Example
cout << (10 == 15); // returns 0 (false), because 10 is not equal to 15
Real Life Example
Let's think of a "real life example" where we need to find out if a person is old enough to vote.
In the example below, we use the >= comparison operator to find out if the age (25) is greater than OR equal to the voting age limit, which is set to 18:
Example
int myAge = 25;
int votingAge = 18;
cout << (myAge >= votingAge); // returns 1 (true), meaning 25 year olds are allowed to vote!
Cool, right? An even better approach (since we are on a roll now), would be to wrap the code above in an if...else statement, so we can perform different actions depending on the result:
Example
Output "Old enough to vote!" if myAge is greater than or equal to 18. Otherwise output "Not old enough to vote.":
int myAge = 25;
int votingAge = 18;
if (myAge >= votingAge) {
cout << "Old enough to vote!";
} else {
cout << "Not old enough to vote.";
}
// Outputs: Old enough to vote!
Booleans are the basis for all C++ comparisons and conditions.
You will learn more about conditions (if...else) in the next chapter.
C++ If ... Else
C++ Conditions and If Statements
You already know that C++ supports the usual logical conditions from mathematics:
Less than: a < b
Less than or equal to: a <= b
Greater than: a > b
Greater than or equal to: a >= b
Equal to a == b
Not Equal to: a != b
You can use these conditions to perform different actions for different decisions.
C++ has the following conditional statements:
Use if to specify a block of code to be executed, if a specified condition is true
Use else to specify a block of code to be executed, if the same condition is false
Use else if to specify a new condition to test, if the first condition is false
Use switch to specify many alternative blocks of code to be executed
The if Statement
Use the if statement to specify a block of C++ code to be executed if a condition is true.
Syntax
if (condition) {
// block of code to be executed if the condition is true
}
Note that if is in lowercase letters. Uppercase letters (If or IF) will generate an error.
In the example below, we test two values to find out if 20 is greater than 18. If the condition is true, print some text:
Example
if (20 > 18) {
cout << "20 is greater than 18";
}
We can also test variables:
Example
int x = 20;
int y = 18;
if (x > y) {
cout << "x is greater than y";
}
Example explained
In the example above we use two variables, x and y, to test whether x is greater than y (using the > operator). As x is 20, and y is 18, and we know that 20 is greater than 18, we print to the screen that "x is greater than y".
C++ Else
The else Statement
Use the else statement to specify a block of code to be executed if the condition is false.
Syntax
if (condition) {
// block of code to be executed if the condition is true
} else {
// block of code to be executed if the condition is false
}
Example
int time = 20;
if (time < 18) {
cout << "Good day.";
} else {
cout << "Good evening.";
}
// Outputs "Good evening."
Example explained
In the example above, time (20) is greater than 18, so the condition is false. Because of this, we move on to the else condition and print to the screen "Good evening". If the time was less than 18, the program would print "Good day".
C++ Else If
The else if Statement
Use the else if statement to specify a new condition if the first condition is false.
Syntax
if (condition1) {
// block of code to be executed if condition1 is true
} else if (condition2) {
// block of code to be executed if the condition1 is false and condition2 is true
} else {
// block of code to be executed if the condition1 is false and condition2 is false
}
Example
int time = 22;
if (time < 10) {
cout << "Good morning.";
} else if (time < 20) {
cout << "Good day.";
} else {
cout << "Good evening.";
}
// Outputs "Good evening."
Example explained
In the example above, time (22) is greater than 10, so the first condition is false. The next condition, in the else if statement, is also false, so we move on to the else condition since condition1 and condition2 is both false - and print to the screen "Good evening".
However, if the time was 14, our program would print "Good day."
C++ Short Hand If Else
Short Hand If...Else (Ternary Operator)
There is also a short-hand if else, which is known as the ternary operator because it consists of three operands. It can be used to replace multiple lines of code with a single line. It is often used to replace simple if else statements:
Syntax
variable = (condition) ? expressionTrue : expressionFalse;
Instead of writing:
Example
int time = 20;
if (time < 18) {
cout << "Good day.";
} else {
cout << "Good evening.";
}
You can simply write:
Example
int time = 20;
string result = (time < 18) ? "Good day." : "Good evening.";
cout << result;
C++ Switch Statements
Use the switch statement to select one of many code blocks to be executed.
Syntax
switch(expression) {
case x:
// code block
break;
case y:
// code block
break;
default:
// code block
}
This is how it works:
The switch expression is evaluated once
The value of the expression is compared with the values of each case
If there is a match, the associated block of code is executed
The break and default keywords are optional, and will be described later in this chapter
The example below uses the weekday number to calculate the weekday name:
Example
int day = 4;
switch (day) {
case 1:
cout << "Monday";
break;
case 2:
cout << "Tuesday";
break;
case 3:
cout << "Wednesday";
break;
case 4:
cout << "Thursday";
break;
case 5:
cout << "Friday";
break;
case 6:
cout << "Saturday";
break;
case 7:
cout << "Sunday";
break;
}
// Outputs "Thursday" (day 4)
The break Keyword
When C++ reaches a break keyword, it breaks out of the switch block.
This will stop the execution of more code and case testing inside the block.
When a match is found, and the job is done, it's time for a break. There is no need for more testing.
A break can save a lot of execution time because it "ignores" the execution of all the rest of the code in the switch block.
The default Keyword
The default keyword specifies some code to run if there is no case match:
Example
int day = 4;
switch (day) {
case 6:
cout << "Today is Saturday";
break;
case 7:
cout << "Today is Sunday";
break;
default:
cout << "Looking forward to the Weekend";
}
// Outputs "Looking forward to the Weekend"
C++ While Loop
C++ Loops
Loops can execute a block of code as long as a specified condition is reached.
Loops are handy because they save time, reduce errors, and they make code more readable.
C++ While Loop
The while loop loops through a block of code as long as a specified condition is true:
Syntax
while (condition) {
// code block to be executed
}
In the example below, the code in the loop will run, over and over again, as long as a variable (i) is less than 5:
Example
int i = 0;
while (i < 5) {
cout << i << "\n";
i++;
}
Note: Do not forget to increase the variable used in the condition, otherwise the loop will never end!
C++ Do/While Loop
The Do/While Loop
The do/while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.
Syntax
do {
// code block to be executed
}
while (condition);
The example below uses a do/while loop. The loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested:
Example
int i = 0;
do {
cout << i << "\n";
i++;
}
while (i < 5);
Do not forget to increase the variable used in the condition, otherwise, the loop will never end!
C++ For Loop
When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop:
Syntax
for (statement 1; statement 2; statement 3) {
// code block to be executed
}
Statement 1 is executed (one time) before the execution of the code block.
Statement 2 defines the condition for executing the code block.
Statement 3 is executed (every time) after the code block has been executed.
The example below will print the numbers 0 to 4:
Example
for (int i = 0; i < 5; i++) {
cout << i << "\n";
}
Example explained
Statement 1 sets a variable before the loop starts (int i = 0).
Statement 2 defines the condition for the loop to run (i must be less than 5). If the condition is true, the loop will start over again, if it is false, the loop will end.
Statement 3 increases a value (i++) each time the code block in the loop has been executed.
Another Example
This example will only print even values between 0 and 10:
Example
for (int i = 0; i <= 10; i = i + 2) {
cout << i << "\n";
}
Nested Loops
It is also possible to place a loop inside another loop. This is called a nested loop.
The "inner loop" will be executed one time for each iteration of the "outer loop":
Example
// Outer loop
for (int i = 1; i <= 2; ++i) {
cout << "Outer: " << i << "\n"; // Executes 2 times
// Inner loop
for (int j = 1; j <= 3; ++j) {
cout << " Inner: " << j << "\n"; // Executes 6 times (2 * 3)
}
}
The for-each Loop
There is also a "for-each loop" (introduced in C++ version 11 (2011), which is used exclusively to loop through elements in an array (or other data sets):
Syntax
for (type variableName : arrayName) {
// code block to be executed
}
The following example outputs all elements in an array, using a "for-each loop":
Example
int myNumbers[5] = {10, 20, 30, 40, 50};
for (int i : myNumbers) {
cout << i << "\n";
}
Note: Don't worry if you don't understand the example above. You will learn more about arrays in the C++ Arrays chapter.
C++ Break and Continue
C++ Break
You have already seen the break statement used in an earlier chapter of this tutorial. It was used to "jump out" of a switch statement.
The break statement can also be used to jump out of a loop.
This example jumps out of the loop when i is equal to 4:
Example
for (int i = 0; i < 10; i++) {
if (i == 4) {
break;
}
cout << i << "\n";
}
C++ Continue
The continue statement breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.
This example skips the value of 4:
Example
for (int i = 0; i < 10; i++) {
if (i == 4) {
continue;
}
cout << i << "\n";
}
Break and Continue in While Loop
You can also use a break and continue in while loops:
Break Example
int i = 0;
while (i < 10) {
cout << i << "\n";
i++;
if (i == 4) {
break;
}
}
Continue Example
int i = 0;
while (i < 10) {
if (i == 4) {
i++;
continue;
}
cout << i << "\n";
i++;
}
C++ Arrays
Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.
To declare an array, define the variable type, specify the name of the array followed by square brackets and specify the number of elements it should store:
string cars[4];
We have now declared a variable that holds an array of four strings. To insert values to it, we can use an array literal - place the values in a comma-separated list, inside curly braces:
string cars[4] = {"Volvo", "BMW", "Ford", "Mazda"};
To create an array of three integers, you could write:
int myNum[3] = {10, 20, 30};
Access the Elements of an Array
You access an array element by referring to the index number inside square brackets [].
This statement accesses the value of the first element in cars:
Example
string cars[4] = {"Volvo", "BMW", "Ford", "Mazda"};
cout << cars[0];
// Outputs Volvo
Note: Array indexes start with 0: [0] is the first element. [1] is the second element, etc.
Change an Array Element
To change the value of a specific element, refer to the index number:
cars[0] = "Opel";
Example
string cars[4] = {"Volvo", "BMW", "Ford", "Mazda"};
cars[0] = "Opel";
cout << cars[0];
// Now outputs Opel instead of Volvo
C++ Arrays and Loops
Loop Through an Array
You can loop through the array elements with the for loop.
The following example outputs all elements in the cars array:
Example
string cars[5] = {"Volvo", "BMW", "Ford", "Mazda", "Tesla"};
for (int i = 0; i < 5; i++) {
cout << cars[i] << "\n";
}
This example outputs the index of each element together with its value:
Example
string cars[5] = {"Volvo", "BMW", "Ford", "Mazda", "Tesla"};
for (int i = 0; i < 5; i++) {
cout << i << " = " << cars[i] << "\n";
}
And this example shows how to loop through an array of integers:
Example
int myNumbers[5] = {10, 20, 30, 40, 50};
for (int i = 0; i < 5; i++) {
cout << myNumbers[i] << "\n";
}
The for-each Loop
There is also a "for-each loop" (introduced in C++ version 11 (2011), which is used exclusively to loop through elements in an array:
Syntax
for (type variableName : arrayName) {
// code block to be executed
}
The following example outputs all elements in an array, using a "for-each loop":
Example
int myNumbers[5] = {10, 20, 30, 40, 50};
for (int i : myNumbers) {
cout << i << "\n";
}
C++ Omit Array Size
Omit Array Size
In C++, you don't have to specify the size of the array. The compiler is smart enough to determine the size of the array based on the number of inserted values:
string cars[] = {"Volvo", "BMW", "Ford"}; // Three arrays
The example above is equal to:
string cars[3] = {"Volvo", "BMW", "Ford"}; // Also three arrays
However, the last approach is considered as "good practice", because it will reduce the chance of errors in your program.
Omit Elements on Declaration
It is also possible to declare an array without specifying the elements on the declaration, and add them later:
Example
string cars[5];
cars[0] = "Volvo";
cars[1] = "BMW";
...
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