In C++, methods are also known as functions. A function is a block of code that performs a specific task and can be called from different parts of a program. Here’s an example of how to create and use a function in C++:

#include <iostream>

// Function declaration
int addNumbers(int a, int b);

int main() {
    int x = 5;
    int y = 10;
    int result = addNumbers(x, y);
    
    std::cout << "The sum of " << x << " and " << y << " is " << result << std::endl;
    
    return 0;
}

// Function definition
int addNumbers(int a, int b) {
    return a + b;
}

In this code, a function called addNumbers is declared and defined. The function takes two integer parameters a and b, and returns the sum of the two parameters.

In the main function, we declare two integer variables x and y, and initialize them with the values 5 and 10 respectively. We then call the addNumbers function and pass in x and y as arguments. The return value of the function is assigned to a variable called result.

Finally, we print a message to the console that displays the values of x, y, and result using std::cout.

Functions can also be used to modify the values of variables. Here’s an example of how to create a function that modifies the value of a variable:

#include <iostream>

// Function declaration
void square(int& x);

int main() {
    int y = 5;
    square(y);
    
    std::cout << "The square of 5 is " << y << std::endl;
    
    return 0;
}

// Function definition
void square(int& x) {
    x = x * x;
}

In this code, a function called square is declared and defined. The function takes an integer reference parameter x, which means that any changes made to x inside the function will affect the original variable passed in as an argument.

In the main function, we declare an integer variable y and initialize it with the value 5. We then call the square function and pass in y as an argument. The square function squares the value of y, which modifies the original variable. Finally, we print a message to the console that displays the value of y using std::cout.