Keywords in C++ : Different Types with Examples

When you first start learning C++, the huge number of keywords may overwhelm you. Everybody has been there. Writing quality code requires familiarity with this large number of keywords in C++.

These keywords have special meanings, and using them correctly is key to mastering the language.

There are a total of 95 keywords that form the backbone of C++ programming. From managing control flow to defining data types and handling memory, keywords make C++ versatile and robust.

For a beginner, the number of keywords might seem overwhelming. But each keyword plays a vital role and understanding them will unlock the full potential of C++.

In this blog, we shall examine these keywords, their significance, and their use.

Tokens in C++ and Their Classification

In C++, the smallest building blocks of a program are tokens. Think of tokens as the basic ingredients in a recipe.

Types of Tokens:

Each token type has a role in making your C++ program run smoothly.

Detailed Explanation of Common C++ Keywords

Understanding the most common C++ keywords helps in writing effective code.

1. auto

The auto keyword lets the compiler deduce the type of a variable from its initializer.

2. bool

The bool keyword defines a boolean variable that can be true or false.

3. break

The break keyword exits a loop or switch statement immediately.

4. case

The case keyword defines a branch in a switch statement.

5. catch

The catch keyword handles exceptions thrown by try.

6. char

The char keyword defines a character variable.

7. class

The class keyword defines a user-defined type with data and functions.

8. const

The const keyword defines variables whose values cannot change.

9. continue

The continue keyword skips the current iteration of a loop and moves to the next.

10. default

The default keyword specifies the default block of code in a switch statement.

11. delete

The delete keyword deallocates memory that was previously allocated with new.

12. double

The double keyword refers to double-precision floating-point variables.

13. else

The else keyword is used in combination with if to provide a different block of code to run if the condition is false.

14. enum

The enum keyword specifies an enumeration, which is a user-defined data type made up of named integer constants.

15. explicit

The explicit keyword disables implicit conversions and copy-initialization of constructors and conversion operators.

16. float

The float keyword defines single-precision floating-point variables.

17. for

The for keyword initiates a loop that iterates over a range of values.

18. friend

The friend keyword allows a function or another class to access private or protected members of a class.

19. int

The int keyword defines integer variables.

20. long

The long keyword defines long integer variables.

21. mutable

The mutable keyword allows a member of a const object to be modified.

22. new

The new keyword allocates memory dynamically.

23. operator

The operator keyword is used to overload operators.

24. private

The private keyword indicates that class members are only available within the class.

25. protected

The protected keyword indicates that class members are available inside the same and derived classes.

26. public

The public keyword indicates that class members are available from outside the class.

27. register

The register keyword indicates that the compiler saves the variable in a register.

28. return

The return keyword retrieves a value from a function.

29. short

The short keyword refers to short integer variables.

30. sizeof

The sizeof keyword calculates the size of a data type or object in bytes.

31. static

The static keyword refers to static members or variables that preserve their value between function calls.

32. struct

The struct keyword defines a structure, a user-defined data type that groups related variables.

33. switch

The switch keyword implements a multi-way branch statement.

34. this

The ‘this’ keyword refers to the current instance of a class.

35. throw

The throw keyword throws an exception.

36. true

The true keyword represents the boolean value true.

37. try

The try keyword begins a block of code that will be tested for exceptions.

38. typedef

A data type’s alias is created using the typedef keyword.

39. union

The union keyword specifies a union as a user-defined data type that can only carry one non-static data member at a time.

40. virtual

For polymorphism, virtual functions are defined with the virtual keyword.

41. void

The void keyword specifies that a function does not return a value.

42. volatile

The volatile keyword indicates that the value of a variable can change at any point without requiring any action from the code.

43. while

The while keyword starts a loop that lasts as long as a condition is true.

Keywords Unique to C++ and Their Significance

Ever wondered what makes C++ unique? It’s the special keywords not found in C. These keywords give C++ its powerful features.

Here are the unique 30 Keywords in C++ Language which are not available in C language:

asm	dynamic_cast	namespace	reinterpret_cast	bool
explicit	new	static_cast	false	catch
operator	template	friend	private	class
this	inline	public	throw	const_cast
delete	mutable	protected	true	try
typeid	typename	using	virtual	wchar_t

Let’s dive into a few examples.

1. class

The class keyword allows us to create our own data types.

2. virtual

The virtual keyword supports dynamic polymorphism.

3. namespace

The namespace keyword helps organize code.

4. explicit

The explicit keyword prevents unwanted implicit conversions.

5. constexpr

The constexpr keyword is used to compile time constants.

6. nullptr

The nullptr keyword represents a null pointer.

#include<iostream> 

using namespace std;

int main() {

    const int maxScore = 100;

    cout << "Max Score: " << maxScore << endl;

    // maxScore = 110; // Error: cannot modify a const variable

    return 0;

}

Max Score: 100

#include<iostream>

using namespace std;

volatile int timer = 0;

int main() {

timer = 10;

cout << "Timer: " << timer << endl;

return 0;

}

Timer: 10

#include<iostream> 

using namespace std;

class Data {

public:

mutable int counter;

Data() : counter(0) {}

};
int main() {

const Data d;

d.counter = 10;

cout << "Counter: " << d.counter << endl;

return 0;

}

Counter: 10

#include<iostream>

using namespace std;

void updateValue(int* restrict ptr, int value) {

*ptr = value;

}

int main() {

int x = 5;

updateValue(&x, 10);

cout << "Updated Value: " << x << endl;

return 0;

}

Updated Value: 10

Differences Between Keywords and Identifiers in C++

Keywords and identifiers are essential in C++ but serve different purposes.

Keywords:

• Reserved words.
• Have predefined meanings.
• Cannot be used as identifiers.

Identifiers:

• Names for variables, functions, etc.
• Defined by the programmer.
• Must follow naming rules.

Comparison Table:

Aspect	Keywords	Identifiers
Definition	Predefined reserved words	User-defined names
Case Sensitivity	Always in lowercase	Can start with uppercase or lowercase
Purpose	Defines the type of entity	Classifies the name of the entity
Character Composition	Only alphabetical characters	alphabets, digits, and underscores
Special Symbols	No special symbols or punctuations	Only underscores are allowed
Examples	int, char, while, do	Hero_Vired, HV, Hv1
Reserved for Syntax	Reserved for specific syntax and functionality	Created by coders for their program
Usage	To declare data types, control structures, etc.	For naming variables, functions, etc.

Reserved Identifiers and Special Identifiers in C++

Have you ever been surprised by identifiers that begin with an underscore? You’re not alone. Reserved and special identifiers can trip up even seasoned programmers.

In C++, some identifiers are reserved. They include:

• Identifiers with double underscores (__).
• Identifiers starting with an underscore followed by an uppercase letter.
• Identifiers starting with an underscore in the global namespace.

Examples:

• __func__: Used to access the name of the current function.
• _MyVariable: Reserved if used at the global scope.

Some identifiers have special meanings.

Examples:

• final: Used in class declarations to prevent inheritance.
• override: Ensures a method overrides a base class method.

These identifiers ensure consistent and error-free code.

#include<iostream>

using namespace std;

int main() {

auto x = 10;

auto y = 3.14;

cout << "x: " << x << ", y: " << y << endl;

return 0;

}

x: 10, y: 3.14

#include<iostream>

using namespace std;

int main() {

try {

throw runtime_error("An error occurred");

} catch (const runtime_error& e) {

cout << "Caught: " << e.what() << endl;

}

return 0;

}

Caught: An error occurred

#include <iostream>

using namespace std; 

int main() {

int* numbers = new int[5];

for (int i = 0; i < 5; ++i) {

numbers[i] = i * 2;

}

for (int i = 0; i < 5; ++i) {

cout << numbers[i] << " ";

}

delete[] numbers;

return 0;

}

0 2 4 6 8

#include<iostream>
using namespace std;

constexpr int square(int x) {

return x * x;

}

int main() {

int result = square(5);

cout << "Square: " << result << endl;

return 0;

}

Square: 25

#include <iostream>

using namespace std; 

class Animal {

public:

virtual void sound() {

cout << "Animal sound";

}

}; 

class Dog : public Animal {

public:

void sound() override {

cout << "Bark";

}

};

int main() {

Animal* a = new Dog();

a->sound();

delete a;

return 0;

}

Bark

Conclusion

In this blog, we explored the core and unique keywords in C++. We looked at examples of keywords such as auto, try, catch, new, and virtual.

These examples demonstrated how these keywords function. Understanding these can help you write cleaner and more effective code.

We also distinguished between keywords and identifiers, ensuring clarity in naming conventions.

By mastering these keywords, we can write cleaner, more efficient C++ code. Keep practicing these concepts to strengthen your programming skills and make your C++ journey more rewarding.