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A reference in C++ is a variable that refers to another variable. References are similar to pointers, but they are more efficient and easier to use.

To declare a reference in C++, you use the & operator. For example:

int x = 10;

int& y = x;

 

This declares a reference named y that refers to the variable x. Once a reference is initialized, it cannot be changed to refer to another variable.

You can use references to access and modify the values of the variables they refer to. For example:

y++;

 

This will increment the value of the variable x, because y refers to x.

References are often used in function parameters and return values. For example:

void swap(int& x, int& y) {

  int temp = x;

  x = y;

  y = temp;

}

 

This function swaps the values of the variables that are passed to it as parameters.

References can also be used to create aliases for variables. For example:

int& z = x;

 

This creates an alias named z for the variable x. You can then use z to access and modify the value of x.

References are a powerful tool that can be used to improve the efficiency and readability of your code. They are especially useful in function parameters and return values.

Here are some additional examples of using references in C++:

// Pass a reference to a function parameter.

void print_value(int& value) {

  std::cout << value << std::endl;

}

 

// Return a reference from a function.

int& get_value() {

  return x;

}

 

// Use a reference to create an alias for a variable.

int& max_value = get_value();

 

// Use the reference to access and modify the value of the variable.

max_value++;

 

// Print the value of the variable.

print_value(max_value);

 

Output:

11