In C++, you can provide default argument values for a function's parameters, which allows you to call the function with fewer arguments than there are parameters.

Here's an example of a function with default argument values:

int multiply(int a, int b = 1) {
    return a * b;
}

In this function, a is a required parameter, and b has a default value of 1. This means that if you call the function with only one argument, b will automatically be set to 1.

int result1 = multiply(3, 4);   // result1 is 12
int result2 = multiply(5);      // result2 is 5, because b is set to 1 by default

In the first example, a is set to 3 and b is set to 4. In the second example, a is set to 5 and b is set to the default value of 1.

Note that default arguments can only be specified in the function declaration, not in the function definition. If you provide a default value in the declaration, you do not need to provide it again in the definition.

// Function declaration with default argument
int multiply(int a, int b = 1);

// Function definition
int multiply(int a, int b) {
    return a * b;
}

When you call a function with default argument values, you can still specify a value for the parameter with the default value, if you want to override the default.

int result1 = multiply(3);      // result1 is 3, because b is set to 1 by default
int result2 = multiply(5, 2);   // result2 is 10, because b is set to 2 explicitly