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.