CS110 Lab: C++ Function with Value-parameters

A variable declared in the heading of a function is called a parameter, also called a formal argument or a formal parameter. A variable or expression included in the call to a function is referred to as an argument, also known as an actual argument or actual parameter. Please read the following for further information:

• A parameter is a value parameter if its data type does not end with an ampersand (&).
• There must be the same number of arguments in a function call as there are parameters in the heading of the function.
• Each argument should have the same data type as the parameter in the same position.
• When the function is called, a copy of the value of the argument is passed to the function. Therefore, the caller argument cannot be accessed directly or changed.
• When the function returns, the contents of its value parameters are destroyed, along with the local variables.
• The difference between value parameters and local variables is that the values of local variables are undefined when a function starts to execute, whereas value parameters are automatically initialized to the values of corresponding arguments.

Example

            
// Program starsNum prints num_stars on the screen.

#include <iostream>
using namespace std;

// printStars prints num_stars stars on the screen.
void printStars(int); //Function prototype, with one integer parameter

int main ()
{
    int num_stars;

    cout  << "How many stars do you want to print out? Enter an integer: ";
    cin >> num_stars;
    cout << endl;

    cout  << "The next line contains "  << num_stars << " stars. "  << endl;
    printStars(num_stars);  //Function call

    return 0;
}

//**********************************************************************
//Function definition, with one integer parameter
//**********************************************************************
// Post: numofstars asterisks are sent to cout.
void printStars (int numOfStars)
{
    int i;
    i = 0;
    while (i < numOfStars)
    {
        cout << "*";
        i++;
    }

    // Here is a for loop which does the same thing 
	// that the above while loop does.
	//
    // for (i=0; i < numOfStars; i++)
    // {   
    //     cout << "*";
    // }

    cout << endl;

    return;
}                                                               

In the above example, the heading of printStars() function is void printStars(int numOfStars).

The parameter numOfStars is a value parameter because its data type int does not end with an ampersand ( & ). When it is called using the argument num_stars, i.e. printStars(num_stars);, then parameter numOfStars receives a copy of the value of num_stars.

While the function runs there are two copies of the data: one in the argument num_stars and one in the parameter numOfStars. If a statement inside the function printStars() were to change the value of numOfStars, this change would not affect the argument num_stars.