C++ Keywords Reference

A keyword is a word that is reserved by the C++ language itself, such as int, if, or class. Keywords have a fixed meaning to the compiler, so you cannot use them as names for variables, functions, or classes.

Why keywords matter

You have already met many keywords in earlier lessons without necessarily calling them that — int, return, if, and for are all keywords. This lesson collects the most commonly used ones in one place so you have a quick reference to come back to.

Common keyword categories

Types

These keywords name or modify built-in data types.

Keyword	Meaning
int	Whole number type
double	Floating-point number type
char	Single character type
bool	Boolean type (true or false)
void	Represents “no value”, used for functions that return nothing
const	Marks a value as unable to change after initialization
unsigned	Restricts an integer type to non-negative values

Control flow

Keyword	Meaning
if / else	Branch based on a condition
for	Loop a known number of times
while	Loop while a condition stays true
do	Loop body runs at least once, checked at the end
switch / case	Branch on one of several fixed values
break	Exit a loop or switch early
continue	Skip to the next loop iteration
return	Exit a function, optionally sending back a value

Classes and object-oriented code

Keyword	Meaning
class / struct	Define a new type made of data and functions
public	Members accessible from outside the class
private	Members accessible only inside the class
protected	Members accessible in the class and its derived classes
static	A member shared by all objects of a class, rather than one per object
this	Pointer to the current object inside a member function
virtual	Allows a derived class to override a function
new / delete	Allocate and free memory on the heap

A few more useful ones

Keyword	Meaning
namespace	Groups names together to avoid naming clashes
using	Brings a name into the current scope, e.g. using namespace std;
true / false	The two boolean literal values
sizeof	Gives the size in bytes of a type or variable
enum	Defines a type with a fixed set of named values
auto	Lets the compiler infer a variable’s type from its initializer

This is not the full list — C++ has around 90 keywords in total, including newer ones like nullptr and constexpr — but the tables above cover the ones you will use in almost every program.

Example

The program below uses several keywords from the tables above: class, public, static, const, void, for, if, else, and return.

#include <iostream>
using namespace std;

class Counter {
public:
    static const int max_value = 5;

    void run() {
        for (int i = 0; i < max_value; i++) {
            if (i % 2 == 0) {
                cout << i << " is even" << endl;
            } else {
                cout << i << " is odd" << endl;
            }
        }
    }
};

int main(void) {
    Counter c;
    c.run();
    return 0;
}

Output:

0 is even
1 is odd
2 is even
3 is odd
4 is even

How it works

static const int max_value belongs to the Counter class itself rather than to any one object, and const guarantees it cannot be changed. The public keyword makes run() callable from outside the class. Inside run(), the for loop uses if/else to decide what to print, and main uses return 0; to signal the program finished successfully.

Keep this page bookmarked as a quick lookup — the next lesson moves on to C++ operators.