Chapter 6 Functions
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Starting Out with C++, 3rd Edition
6.1 Focus on Software Engineering:
Breaking Up Your Programs
• Programs may be broken up into many
manageable functions.
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Starting Out with C++, 3rd Edition
6.2 Defining and Calling Functions
• A function call is a statement that causes a
function to execute. A function definition contains
the statements that make up the function.
• The line in the definition that reads void
main(void) is called the function header.
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Starting Out with C++, 3rd Edition
Figure 6-1
Return Type
Parameter List (This one is empty)
Name
Body
void main(void)
{
cout << “Hello World\n”;
}
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Starting Out with C++, 3rd Edition
Calling a Function
• Function Header
void displayMessage()
• Function Call
displayMessage();
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Starting Out with C++, 3rd Edition
Program 6-1
#include <iostream.h>
//******************************************
// Definition of function displayMessage. *
// This function displays a greeting.
*
//******************************************
void displayMessage()
{
cout << "Hello from the function displayMessage.\n";
}
void main(void)
{
cout << "Hello from main.\n";
displayMessage();
cout << "Back in function main again.\n";
}
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Starting Out with C++, 3rd Edition
Program Output
Hello from main.
Hello from the function displayMessage.
Back in function main again.
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Starting Out with C++, 3rd Edition
Figure 6-2
void displayMessage()
{
cout << “Hello from the function displayMessage.\n”;
}
void main(void)
{
cout << “Hello from main.\n”;
displayMessage();
cout << “Back in function main again.\n”;
}
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Starting Out with C++, 3rd Edition
Program 6-2
//The function displayMessage is repeatedly called from a loop
#include <iostream.h>
//******************************************
// Definition of function displayMessage. *
// This function displays a greeting.
*
//******************************************
void displayMessage()
{
cout << "Hello from the function displayMessage.\n";
}
void main(void)
{
cout << "Hello from main.\n";
for (int count = 0; count < 5; count++)
displayMessage();
// Call displayMessage
cout << "Back in function main again.\n";
}
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Starting Out with C++, 3rd Edition
Program Output
Hello from main.
Hello from the function displayMessage.
Hello from the function displayMessage.
Hello from the function displayMessage.
Hello from the function displayMessage.
Hello from the function displayMessage.
Back in function main again.
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Starting Out with C++, 3rd Edition
Program 6-3
// This program has three functions: main, first, and second.
#include <iostream.h>
//*************************************
// Definition of function first.
*
// This function displays a message. *
//*************************************
void first(void)
{
cout << "I am now inside the function first.\n";
}
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Starting Out with C++, 3rd Edition
Program continues
//*************************************
// Definition of function second.
*
// This function displays a message. *
//*************************************
void second(void)
{
cout << "I am now inside the function second.\n";
}
void main(void)
{
cout << "I am
first();
//
second(); //
cout << "Back
}
starting in function main.\n";
Call function first
Call function second
in function main again.\n";
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Starting Out with C++, 3rd Edition
Program Output
I am starting in function main.
I am now inside the function first.
I am now inside the function second.
Back in function main again.
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Starting Out with C++, 3rd Edition
Figure 6-3
void first(void)
{
cout << “I am now inside function first.\n”;
}
void second(void)
{
cout << “I am now inside function second.\n”;
}
void main(void)
{
cout << “I am starting in function main.\n”;
first();
second();
cout << “Back in function main again.\n”
}
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Starting Out with C++, 3rd Edition
Program 6-4
// This program has three functions: main, deep, and deeper
#include <iostream.h>
//**************************************
// Definition of function deeper.
*
// This function displays a message.
*
//**************************************
void deeper(void)
{
cout << "I am now inside the function deeper.\n";
}
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Starting Out with C++, 3rd Edition
Program continues
//**************************************
// Definition of function deep.
*
// This function displays a message.
*
//**************************************
void deep()
{
cout << "I am now inside the function deep.\n";
deeper(); // Call function deeper
cout << "Now I am back in deep.\n";
}
void main(void)
{
cout << "I am starting in function main.\n";
deep();
// Call function deep
cout << "Back in function main again.\n";
}
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Starting Out with C++, 3rd Edition
Program Output
I am starting in function main.
I am now inside the function deep.
I am now inside the function deeper.
Now I am back in deep.
Back in function main again.
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Starting Out with C++, 3rd Edition
Figure 6-4
void deep(void)
{
cout << “I am now inside function deep.\n”;
deeper();
cout << “Now I am back in deep.\n”;
}
void deeper(void)
{
cout << “I am now inside function deeper.\n”;
}
void main(void)
{
cout << “I am starting in function main.\n”;
deep();
cout << “Back in function main again.\n”
}
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Starting Out with C++, 3rd Edition
6.3 Function Prototypes
• A function prototype eliminates the need to place a
function definition before all calls to the function.
• Here is a prototype for the displayMessage
function in Program 6-1
void displayMessage(void);
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Starting Out with C++, 3rd Edition
Program 6-5
// This program has three functions: main, first, and second.
#include <iostream.h>
// Function Prototypes
void first(void);
void second(void);
void main(void)
{
cout << "I am
first();
//
second(); //
cout << “Back
}
starting in function main.\n";
Call function first
Call function second
in function main again.\n";
Program Continues on next slide
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Starting Out with C++, 3rd Edition
Program 6-5 Continues
// Definition of function first.
// This function displays a message.
void first(void)
{
cout << “I am now inside the function first.\n”;
}
// Definition of function second
// This function displays a message.
void second(void)
{
cout << “I am now inside the function second.\n”;
}
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Starting Out with C++, 3rd Edition
Program 6-5 Output
I am starting in function main.
I am now inside the function first.
I am now inside the function second.
Back in function main again.
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Starting Out with C++, 3rd Edition
6.4 Sending Information Into a Function
• When a function is called, the program may send
values (arguments) into the function.
• Arguments are passed into parameters.
void displayValue(int num)
{
cout << “The value is “ << num << endl;
}
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Starting Out with C++, 3rd Edition
Program 6-6
// This program demonstrates a function with a parameter.
#include <iostream.h>
// Function Prototype
void displayValue(int)
void main(void)
{
cout << "I am passing 5 to displayValue.\n";
displayValue(5);
//Call displayValue with argument 5
cout << "Now I am back in main.\n";
}
Program Continues to next slide
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Starting Out with C++, 3rd Edition
Program 6-6
//*********************************************
// Definition of function displayValue.
// It uses an integer parameter whose value is displayed.
//*********************************************
*
*
void displayValue(int num)
{
cout << “The value is “ << num << endl;
}
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Starting Out with C++, 3rd Edition
Program Output
I am passing 5 to displayValue.
The value is 5
Now I am back in main.
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Starting Out with C++, 3rd Edition
Figure 6-5
displayValue(5);
void displayValue(int num)
{
cout << “The value is “ << num << endl;
}
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Starting Out with C++, 3rd Edition
Program 6-7
// This program demonstrates a function with a parameter.
#include <iostream.h>
// Function Prototype
void displayValue(int);
void main(void)
{
cout << "I am passing several values to displayValue.\n";
displayValue(5); // Call displayValue with argument 5
displayValue(10); // Call displayValue with argument 10
displayValue(2); // Call displayValue with argument 2
displayValue(16); // Call displayValue with argument 16
cout << "Now I am back in main.\n";
}
Program continues on next slide
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Starting Out with C++, 3rd Edition
Program 6-7 Continued
//*********************************************************
// Definition of function displayValue.
*
// It uses an integer parameter whose value is displayed. *
//*********************************************************
void displayValue(int num)
{
cout << "The value is " << num << endl;
}
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Starting Out with C++, 3rd Edition
Program Output
I am passing several values to displayValue.
The value is 5
The value is 10
The value is 2
The value is 16
Now I am back in main.
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Starting Out with C++, 3rd Edition
Program 6-8
// This program demonstrates a function with three parameters.
#include <iostream.h>
// Function prototype
void showSum(int, int, int);
void main(void)
{
int value1, value2, value3;
cout << "Enter three integers and I will display ";
cout << "their sum: ";
cin >> value1 >> value2 >> value3;
showSum(value1, value2, value3); // Call showSum with
// 3 arguments
}
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Starting Out with C++, 3rd Edition
Program continues
//************************************************************
// Definition of function showSum.
*
// It uses three integer parameters. Their sum is displayed. *
//************************************************************
void showSum(int num1, int num2, int num3)
{
cout << (num1 + num2 + num3) << endl;
}
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Starting Out with C++, 3rd Edition
Program Output with Example Input
Enter three integers and I will display their sum: 4 8 7
[Enter]
19
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Starting Out with C++, 3rd Edition
Figure 6-6
showSum(value1, value2, value3);
void showSum(int num1, int num2, int num3)
{
cout << num1 + num2 + num3 << endl;
}
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Starting Out with C++, 3rd Edition
6.5 Changing the value of a Parameter
• When an argument is passed into a
parameter, only a copy of the argument’s
value is passed. Changes to the parameter
do not affect the original argument. This is
called “passed by value.”
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Starting Out with C++, 3rd Edition
Program 6-9
// This program demonstrates that changes to a function parameter
// have no effect on the original argument.
#include <iostream.h>
// Function Prototype
void changeThem(int, float);
void main(void)
{
int whole = 12;
float real = 3.5;
cout << "In main the value of whole is " << whole << endl;
cout << "and the value of real is " << real << endl;
changeThem(whole, real);
// Call changeThem with 2 arguments
cout << "Now back in main again, the value of ";
cout << "whole is " << whole << endl;
cout << "and the value of real is " << real << endl;
}
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Starting Out with C++, 3rd Edition
Program continues
//**************************************************************
// Definition of function changeThem.
*
// It uses i, an int parameter, and f, a float. The values of *
// i and f are changed and then displayed.
*
//**************************************************************
void changeThem(int i, float f)
{
i = 100;
f = 27.5;
cout << "In changeThem the value of i is changed to ";
cout << i << endl;
cout << "and the value of f is changed to " << f << endl;
}
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Starting Out with C++, 3rd Edition
Program Output
In main the value of whole is 12
and the value of real is 3.5
In changeThem the value of i is changed to 100
and the value of f is changed to 27.5
Now back in main again, the value of whole is 12
and the value of real is 3.5
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Starting Out with C++, 3rd Edition
Figure 6-7
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Starting Out with C++, 3rd Edition
6.6 Focus on Software Engineering: Using
Functions in a Menu-Driven Program
• Functions are ideal for use in menu-driven programs.
When the user selects an item from a menu, the program
can call the appropriate function.
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Starting Out with C++, 3rd Edition
Program 6-10
// This is a menu-driven program that makes a function call
// for each selection the user makes.
#include <iostream.h>
// Function Prototypes
void adult(int);
void child(int);
void senior(int);
void main(void)
{
int choice, months;
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Starting Out with C++, 3rd Edition
Program continues
cout.setf(ios::fixed | ios::showpoint);
cout.precision(2);
do
{
cout << "\n\t\tHealth Club Membership Menu\n\n";
cout << "1. Standard adult Membership\n";
cout << "2. child Membership\n";
cout << "3. senior Citizen Membership\n";
cout << "4. Quit the Program\n\n";
cout << "Enter your choice: ";
cin >> choice;
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Starting Out with C++, 3rd Edition
Program continues
if (choice != 4)
{
cout << "For how many months? ";
cin >> months;
}
switch (choice)
{
case 1:
adult(months);
break;
case 2:
child(months);
break;
case 3:
senior(months);
break;
case 4:
cout << "Thanks for using this ";
cout << "program.\n";
break;
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Starting Out with C++, 3rd Edition
Program continues
default:
cout << "The valid choices are 1-4. ";
cout << "Try again.\n";
}
} while (choice != 4);
}
//***********************************************************
// Definition of function adult. Uses an integer parameter, mon.
*
// mon holds the number of months the membership should be
*
// calculated for. The cost of an adult membership for that many
*
// months is displayed.
*
//******************************************************************
void adult(int mon)
{
cout << "The total charges are $";
cout << (mon * 40.0) << endl;
}
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Starting Out with C++, 3rd Edition
Program continues
//********************************************************************
// Definition of function child. Uses an integer parameter, mon.
*
// mon holds the number of months the membership should be
*
// calculated for. The cost of a child membership for that many
*
// months is displayed.
*
//*************************************************************
void child(int mon)
{
cout << "The total charges are $";
cout << (mon * 20.0) << endl;
}
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Starting Out with C++, 3rd Edition
Program continues
//*******************************************************************
// Definition of function senior. Uses an integer parameter, mon.
*
// mon holds the number of months the membership should be
*
// calculated for. The cost of a senior citizen membership for
*
// that many months is displayed.
*
//************************************************************
void senior(int mon)
{
cout << "The total charges are $";
cout << (mon * 30.0) << endl;
}
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Starting Out with C++, 3rd Edition
Program Output with Example Input
Health Club Membership Menu
1. Standard adult Membership
2. child Membership
3. senior Citizen Membership
4. Quit the Program
Enter your choice: 1
For how many months 12
The total charges are $480.00
Health Club Membership Menu
1. Standard adult Membership
2. child Membership
3. senior Citizen Membership
4. Quit the Program
Enter your choice: 4
Thanks for using this program.
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Starting Out with C++, 3rd Edition
6.7 The return Statement
• The return statement causes a function to
end immediately.
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Starting Out with C++, 3rd Edition
Program 6-11
// This program demonstrates a function with a return
statement.
#include <iostream.h>
// Function prototype
void halfway(void);
void main(void)
{
cout << "In main, calling halfway...\n";
halfway();
cout << "Now back in main.\n";
}
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Starting Out with C++, 3rd Edition
Program continues
//*********************************************************
// Definition of function halfway.
*
// This function has a return statement that forces it to *
// terminate before the last statement is executed.
*
//*********************************************************
void halfway(void)
{
cout << "In halfway now.\n";
return;
cout <<"Will you ever see this message?\n";
}
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Starting Out with C++, 3rd Edition
Program Output
In main, calling halfway...
In halfway now.
Now back in main.
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Starting Out with C++, 3rd Edition
Program 6-12
// This program uses a function to perform division. If division
// by zero is detected, the function returns.
#include <iostream.h>
// Function prototype.
void divide(float, float);
void main(void)
{
float num1, num2;
cout << "Enter two numbers and I will divide the first\n";
cout << "number by the second number: ";
cin >> num1 >> num2;
divide(num1, num2);
}
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Starting Out with C++, 3rd Edition
Program continues
//****************************************************************
// Definition of function divide.
*
// Uses two parameters: arg1 and arg2. The function divides arg1 *
// by arg2 and shows the result. If arg2 is zero, however, the
*
// function returns.
*
//****************************************************************
void divide(float arg1, float arg2)
{
if (arg2 == 0.0)
{
cout << "Sorry, I cannot divide by zero.\n";
return;
}
cout << "The quotient is " << (arg1 / arg2) << endl;
}
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Starting Out with C++, 3rd Edition
Program Output with Example Input
Enter two numbers and I will divide the first
number by the second number: 12 0 [Enter]
Sorry, I cannot divide by zero.
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Starting Out with C++, 3rd Edition
6.8 Returning a value From a Function
• A function may send a value back to the
part of the program that called the function.
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Starting Out with C++, 3rd Edition
Figure 6-10
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Starting Out with C++, 3rd Edition
Program 6-13
// This program uses a function that returns a value.
#include <iostream.h>
//Function prototype
int square(int);
void main(void)
{
int value, result;
cout << "Enter a number and I will square it: ";
cin >> value;
result = square(value);
cout << value << " squared is " << result << endl;
}
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Starting Out with C++, 3rd Edition
Program continues
//****************************************************
// Definition of function square.
*
// This function accepts an int argument and returns *
// the square of the argument as an int.
*
//****************************************************
int square(int number)
{
return number * number;
}
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Starting Out with C++, 3rd Edition
Program Output with Example Input
Enter a number and I will square it: 20 [Enter]
20 squared is 400
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Starting Out with C++, 3rd Edition
Figure 6-11
result = square(value);
20
int square(int number)
{
return number * number;
}
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Starting Out with C++, 3rd Edition
6.9 Returning Boolean Values
• Function may return true or false
values.
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Starting Out with C++, 3rd Edition
Program 6-15
// This program uses a function that returns true or false.
#include <iostream.h>
// Function prototype
bool isEven(int);
void main(void)
{
int val;
cout << "Enter an integer and I will tell you ";
cout << "if it is even or odd: ";
cin >> val;
if (isEven(val))
cout << val << " is even.\n";
else
cout << val << " is odd.\n";
}
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Starting Out with C++, 3rd Edition
Program continues
//*********************************************************************
// Definition of function isEven. This function accepts an
*
// integer argument and tests it to be even or odd. The function
*
// returns true if the argument is even or false if the argument is
*
// odd.
*
// The return value is bool.
*
//*********************************************************************
bool isEven(int number)
{
bool status;
if (number % 2)
status = false; // The number is odd if there's a remainder.
else
status = true; // Otherwise, the number is even.
return status;
}
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Starting Out with C++, 3rd Edition
Program Output
Enter an integer and I will tell you if it is even or odd: 5
[Enter]
5 is odd.
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Starting Out with C++, 3rd Edition
6.10 Local and Global Variables
• A local variable is declared inside a
function, and is not accessible outside the
function.
• A global variable is declared outside all
functions and is accessible in its scope.
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Starting Out with C++, 3rd Edition
Program 6-16
// This program shows that variables declared in a function
// are hidden from other functions.
#include <iostream.h>
void func(void);
// Function prototype
void main(void)
{
int num = 1;
cout << "In main, num is " << num << endl;
func();
cout << "Back in main, num is still " << num << endl;
}
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Starting Out with C++, 3rd Edition
Program continues
//*********************************************************
// Definition of function func.
*
// It has a local variable, num, whose initial value, 20, *
// is displayed.
*
//*********************************************************
void func(void)
{
int num = 20;
cout << "In func, num is " << num << endl;
}
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Starting Out with C++, 3rd Edition
Program Output
In main, num is 1
In func, num is 20
Back in main, num is still 1
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Starting Out with C++, 3rd Edition
Figure 6-8
Function main
num = 1
This num variable is only
visible in function main.
Function func
num = 20
This num variable is only
visible in function func.
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Starting Out with C++, 3rd Edition
Program 6-17
// This program shows that a global variable is visible
// to all the functions that appear in a program after
// the variable's declaration.
#include <iostream.h>
void func(void); // Function prototype
int num = 2; // Global variable
void main(void)
{
cout << "In main, num is " << num << endl;
func();
cout << "Back in main, num is " << num << endl;
}
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Starting Out with C++, 3rd Edition
Program continues
//*****************************************************
// Definition of function func.
*
// func changes the value of the global variable num *
//*****************************************************
void func(void)
{
cout << "In func, num is " << num << endl;
num = 50;
cout << "But, it is now changed to " << num << endl;
}
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Starting Out with C++, 3rd Edition
Program Output
In main, num is 2
In func, num is 2
But, it is now changed to 50
Back in main, num is 50
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Starting Out with C++, 3rd Edition
Program 6-18
// This program shows that a global variable is visible
// to all the functions that appear in a program after
// the variable's declaration.
#include <iostream.h>
void func(void); // Function prototype
void main(void)
{
cout << "In main, num is not visible!\n";
func();
cout << "Back in main, num still isn't visible!\n";
}
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Starting Out with C++, 3rd Edition
Program continues
int num = 2; // Global variable
//*****************************************************
// Definition of function func
*
// func changes the value of the global variable num. *
//*****************************************************
void func(void)
{
cout << "In func, num is " << num << endl;
num = 50;
cout << "But, it is now changed to " << num << endl;
}
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Starting Out with C++, 3rd Edition
Program Output
In main, num is not visible!
In func, num is 2
But, it is now changed to 50
Back in main, num still isn't visible!
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Starting Out with C++, 3rd Edition
Global Variables are Initialized to
Zero by Default
• Unless you explicitly initialize numeric
global variables, they are automatically
initialized to zero.
• Global character variables are initialized to
NULL, or ASCII code 0.
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Starting Out with C++, 3rd Edition
Program 6-19
// This program has an uninitialized global variable.
#include <iostream.h>
int globalNum; // Global variable. Automatically set to zero.
void main(void)
{
cout << "globalNum is " << globalNum << endl;
}
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Starting Out with C++, 3rd Edition
Program Output
globalNum is 0
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Starting Out with C++, 3rd Edition
Local and Global Variables with the
Same Name
• If a function has a local variable with the
same name as a global variable, only the
local variable can be seen by the function.
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Starting Out with C++, 3rd Edition
Program 6-20
// This program shows that when a local variable has the
// same name as a global variable, the function only sees
// the local variable.
#include <iostream.h>
// Function prototypes
void texas();
void arkansas();
int cows = 10;
void main(void)
{
cout << "There are " << cows << " cows in main.\n";
texas();
arkansas();
cout << "Back in main, there are " << cows << " cows.\n";
}
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Starting Out with C++, 3rd Edition
Program continues
//******************************************
// Definition of function texas.
*
// The local variable cows is set to 100. *
//******************************************
void texas(void)
{
int cows = 100;
cout << "There are " << cows << " cows in texas.\n";
}
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Starting Out with C++, 3rd Edition
Program continues
//******************************************
// Definition of function arkansas.
*
// The local variable cows is set to 50.
*
//******************************************
void arkansas(void)
{
int cows = 50;
cout << "There are " << cows << " cows in arkansas.\n";
}
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Starting Out with C++, 3rd Edition
Program Output
There are 10 cows in main.
There are 100 cows in texas.
There are 50 cows in arkansas.
Back in main, there are 10 cows.
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Starting Out with C++, 3rd Edition
Program 6-21
// This program has local and global variables. In the function
// ringUpSale, there is a local variable named tax. There is
// also a global variable with the same name.
#include <iostream.h>
void ringUpSale(void); // Function prototype
// Global Variables
const float taxRate = 0.06;
float tax, sale, total;
void main(void)
{
char again;
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Starting Out with C++, 3rd Edition
Program continues
cout.precision(2);
cout.setf(ios::fixed | ios::showpoint);
do
{
ringUpSale();
cout << "Is there another item to be purchased? ";
cin >> again;
} while (again == 'y' || again == 'Y');
tax = sale * taxRate;
total = sale + tax;
cout << "The tax for this sale is " << tax << endl;
cout << "The total is " << total << endl;
}
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Starting Out with C++, 3rd Edition
Program continues
//******************************************************************
// Definition of function ringUpSale.
*
// This function asks for the quantity and unit price of an item. *
// It then calculates and displays the sales tax and subtotal
*
// for those items.
*
//******************************************************************
void ringUpSale(void)
{
int qty;
float unitPrice, tax, thisSale, subTotal;
cout << "Quantity: ";
cin >> qty;
cout << "Unit price: ";
cin >> unitPrice;
thisSale = qty * unitPrice; // Get the total unit price
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Starting Out with C++, 3rd Edition
Program continues
sale += thisSale;
// Update global variable sale
tax = thisSale * taxRate;
// Get sales tax for these items
subTotal = thisSale + tax; // Get subtotal for these items
cout << "Price for these items: " << thisSale << endl;
cout << "tax for these items: " << tax << endl;
cout << "subTotal for these items: " << subTotal << endl;
}
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Starting Out with C++, 3rd Edition
Program Output with Example Input
Quantity: 2 [Enter]
Unit Price: 20.00 [Enter]
Price for these items: 40.00
tax for these items: 2.40
subTotal for these items: 42.40
Is there another item to be purchased? y [Enter]
Quantity: 3 [Enter]
Unit Price: 12.00 [Enter]
Price for these items: 36.00
tax for these items: 2.16
subTotal for these items: 38.16
Is there another item to be purchased? n [Enter]
The tax for this sale is 4.56
The total is 80.56
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Starting Out with C++, 3rd Edition
Be Careful With Global Variables
• It is tempting to make all your variables
global. But don’t do it!
• Using global variables can cause problems.
– It is harder to debug a program that uses global
variables
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6.11 Static Local Variables
• If a function is called more than once in a
program, the values stored in the function’s
local variables do not persist between
function calls.
• To get a variable to keep it’s value even
after the function ends, you must create
static variables
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Program 6-22
// This program shows that local variables do not retain
// their values between function calls.
#include <iostream.h>
// Function prototype
void showLocal(void);
void main(void)
{
showLocal();
showLocal();
}
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Program continues
//***********************************************************
// Definition of function showLocal.
*
// The initial value of localNum, which is 5, is displayed. *
// The value of localNum is then changed to 99 before the
*
// function returns.
*
//***********************************************************
void showLocal(void)
{
int localNum = 5; // Local variable
cout << "localNum is " << localNum << endl;
localNum = 99;
}
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Program Output
localNum is 5
localNum is 5
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Starting Out with C++, 3rd Edition
Program 6-23
//This program uses a static local variable.
#include <iostream.h>
void showStatic(void); // Function prototype
void main(void)
{
for (int count = 0; count < 5; count++)
showStatic();
}
//*************************************************************
// Definition of function showStatic.
*
// statNum is a static local variable. Its value is displayed *
// and then incremented just before the function returns.
*
//*************************************************************
void showStatic(void)
{
static int statNum;
cout << "statNum is " << statNum << endl;
statNum++;
}
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Program Output
statNum is 0
statNum is 1
statNum is 2
statNum is 3
statNum is 4
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Program 6-24
// This program shows that a static local variable is only
// initialized once.
#include <iostream.h>
void showStatic(void); // Function prototype
void main(void)
{
for (int count = 0; count < 5; count++)
showStatic();
}
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Program continues
//***********************************************************
// Definition of function showStatic.
*
// statNum is a static local variable. Its value is displayed
// and then incremented just before the function returns.
*
//***********************************************************
void showStatic()
{
static int statNum = 5;
cout << "statNum is " << statNum << endl;
statNum++;
}
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Starting Out with C++, 3rd Edition
Program Output
statNum is 5
statNum is 6
statNum is 7
statNum is 8
statNum is 9
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6.12 Default Arguments
• Default arguments are passed to parameters
automatically if no argument is provided in
the function call.
• A function’s default arguments should be
assigned in the earliest occurrence of the
function name. This will usually mean the
function prototype.
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Starting Out with C++, 3rd Edition
Program 6-25
// This program demonstrates default function arguments.
#include <iostream.h>
// Function prototype with default arguments
void displayStars(int = 10, int = 1);
void main(void)
{
displayStars();
cout << endl;
displayStars(5);
cout << endl;
displayStars(7, 3);
}
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Program continues
//**************************************************************
// Definition of function displayStars.
*
// The default argument for cols is 10 and for rows is 1.
*
// This function displays a rectangle made of asterisks.
*
//**************************************************************
void displayStars(int cols, int rows)
{
// Nested loop. The outer loop controls the rows
// and the inner loop controls the columns.
for (int down = 0; down < rows; down++)
{
for (int across = 0; across < cols; across++)
cout << "*";
cout << endl;
}
}
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Program Output
**********
*****
*******
*******
*******
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Default Argument Summary
• The value of a default argument must be a constant (either
a literal value of a named constant).
• When an argument is left out of a function call (because it
has a default value), all the arguments that come after it
must be left out too.
• When a function has a mixture of parameters both with and
without default arguments, the parameters with default
arguments must be declared last.
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6.13 Using Reference Variables as
Parameters
• When used as parameters, reference
variables allow a function to access the
parameter’s original argument, changes to
the parameter are also made to the
argument.
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Example:
void doubleNum(int &refVar)
{
refVar *= 2;
}
// The variable refVar is called
// “a reference to an int”
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Program 6-26
// This program uses a reference variable as a function
// parameter.
#include <iostream.h>
// Function prototype. The parameter is a reference variable.
void doubleNum(int &);
void main(void)
{
int value = 4;
cout << "In main, value is " << value << endl;
cout << "Now calling doubleNum..." << endl;
doubleNum(value);
cout << "Now back in main. value is " << value << endl;
}
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Program continues
//************************************************************
// Definition of doubleNum.
*
// The parameter refVar is a reference variable. The value
*
// in refVar is doubled.
*
//************************************************************
void doubleNum (int &refVar)
{
refVar *= 2;
}
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Program Output
In main, value is 4
Now calling doubleNum...
Now back in main. value is 8
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Program 6-27
// This program uses reference variables as function
// parameters.
#include <iostream.h>
// Function prototypes. Both functions use reference variables
// as parameters
void doubleNum(int &);
void getNum(int &);
void main(void)
{
int value;
getNum(value);
doubleNum(value);
cout << "That value doubled is " << value << endl;
}
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Program continues
//*************************************************************
// Definition of getNum.
*
// The parameter userNum is a reference variable. The user is *
// asked to enter a number, which is stored in userNum.
*
//*************************************************************
void getNum(int &userNum)
{
cout << "Enter a number: ";
cin >> userNum;
}
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Program continues
//************************************************************
// Definition of doubleNum.
*
// The parameter refVar is a reference variable. The value
*
// in refVar is doubled.
*
//************************************************************
void doubleNum (int &refVar)
{
refVar *= 2;
}
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Program Output with Example Input
Enter a number: 12 [Enter]
That value doubled is 24
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Reference Argument Warning
• Don’t get carried away with using reference
variables as function parameters. Any time
you allow a function to alter a variable
that’s outside the function, you are creating
potential debugging problems. Reference
variables should only be used as parameters
when the situation demands them.
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6.14 Overloaded Functions
• Two or more functions may have the same
name as long as their parameter lists are
different.
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Program 6-28
#include <iostream.h>
// Function prototypes
int square(int);
float square(float);
void main(void)
{
int userInt;
float userFloat;
cout.precision(2);
cout << "Enter an integer and a floating-point value: ";
cin >> userInt >> userFloat;
cout << "Here are their squares: ";
cout << square(userInt) << " and " << square(userFloat);
}
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Program continues
// Definition of overloaded function square.
// This function uses an int parameter, number. It returns the
// square of number as an int.
int square(int number)
{
return number * number;
}
// Definition of overloaded function square.
// This function uses a float parameter, number. It returns the
// square of number as a float.
float square(float number)
{
return number * number;
}
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Program Output with Example Input
Enter an integer and floating-point value: 12 4.2
[Enter]
Here are their squares: 144 and 17.64
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Program 6-29
// This program demonstrates overloaded functions to calculate
// the gross weekly pay of hourly-paid or salaried employees.
#include <iostream.h>
// Function prototypes
void getChoice(char &);
float calcWeeklyPay(int, float);
float calcWeeklyPay(float);
void main(void)
{
char selection;
int worked;
float rate, yearly;
cout.precision(2);
cout.setf(ios::fixed | ios::showpoint);
cout << “Do you want to calculate the weekly pay of\n";
cout << “(H) an hourly-paid employee, or \n”;
cout << “(S) a salaried employee?\n”;
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Program continues
getChoice(selection);
switch (selection)
{
case ‘H’ :
case ‘h’ :
case ‘S’ :
case ‘s’ :
cout << “How many hours were worked? “;
cin >> worked;
cout << “What is the hour pay rate? “;
cin >> rate;
cout << “The gross weekly pay is “;
cout << calcWeeklyPay(worked, rate);
break;
cout << “What is the annual salary? “;
cin >> yearly;
cout << “The gross weekly pay is “;
cout << calcWeeklyPay(yearly);
break;
}
}
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Program continues
//***********************************************************
// Definition of function getChoice.
*
// The parameter letter is a reference to a char.
*
// This function asks the user for an H or an S and returns *
// the validated input.
*
//***********************************************************
void getChoice(char &letter)
{
do
{
cout << “Enter your choice (H or S): “;
cin >> letter;
} while (letter != ‘H’ && letter != ‘h’ &&
letter != ‘S’ && letter != ‘s’);
}
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Program continues
//***********************************************************
// Definition of overloaded function calcWeeklyPay.
*
// This function calculates the gross weekly pay of
*
// an hourly-paid employee. The parameter hours hold the
*
// hourly pay rate. The function returns the weekly salary. *
//***********************************************************
void calcWeekly(int hours, float payRate)
{
return hours * payRate;
}
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Program continues
//***********************************************************
// Definition of overloaded function calcWeeklyPay.
*
// This function calculates the gross weekly pay of
*
// a salaried employee. The parameter holds the employee’s *
// annual salary. The function returns the weekly salary.
*
//***********************************************************
void calcWeekly(float annSalary)
{
return annSalary / 52.0;
}
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Program Output with Example Input
Do you want to calculate the weekly pay of
(H) an houly-paid employee, or
(S) a salaried employee? H[Enter]
How many hours were worked? 40[Enter]
What is the hour pay rate? 18.50[Enter]
The gross weekly pay is 740.00
Program Output with Other Example Input
Do you want to calculate the weekly pay of
(H) an houly-paid employee, or
(S) a salaried employee? S[Enter]
What is the annual salary? 48000.00[Enter]
The gross weekly pay is 923.08
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6.15 The exit() Function
• The exit() function causes a program to
terminate, regardless of which function or
control mechanism is executing.
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Program 6-30
// This program shows how the exit function causes a program
// to stop executing.
#include <iostream.h>
#include <stdlib.h> // For exit
void function(void);
// Function prototype
void main(void)
{
function();
}
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Program continues
//***********************************************************
// This function simply demonstrates that exit can be used *
// to terminate a program from a function other than main. *
//***********************************************************
void function(void)
{
cout << "This program terminates with the exit
function.\n";
cout << "Bye!\n";
exit(0);
cout << "This message will never be displayed\n";
cout << "because the program has already terminated.\n";
}
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Program Output
This program terminates with the exit function.
Bye!
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Program 6-31
// This program demonstrates the exit function.
#include <iostream.h>
#include <stdlib.h> // For exit
void main(void)
{
char response;
cout << "This program terminates with the exit function.\n";
cout << "Enter S to terminate with the EXIT_SUCCESS code\n";
cout << "or f to terminate with the EXIT_FAILURE code: ";
cin >> response;
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Program continues
if (response == 'S')
{
cout << "Exiting with EXIT_SUCCESS.\n";
exit(EXIT_SUCCESS);
}
else
{
cout << "Exiting with EXIT_FAILURE.\n";
exit(EXIT_FAILURE);
}
}
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Program Output with Example Input
This program terminates with the exit function.
Enter S to terminate with the EXIT_SUCCESS code
or f to terminate with the EXIT_FAILURE code: s [Enter]
Exiting with EXIT_SUCCESS.
Program Output With Other Example Input
This program terminates with the exit function.
Enter S to terminate with the EXIT_SUCCESS code
or f to terminate with the EXIT_FAILURE code: f [Enter]
Exiting with EXIT_FAILURE.
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6.16 Stubs and Drivers
• Stubs and drivers are very helpful tools for
testing and debugging programs that use
functions.
• A stub is a dummy function that is called
instead of the actual function it represents.
• A driver is a program that tests a function
by simply calling it.
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// Stub for the adult function.
void adult(int months)
{
cout << "The function adult was called with " << months;
cout << " as its argument.\n";
}
// Stub for the child function.
void child(int months)
{
cout << "The function child was called with " << months;
cout << " as its argument.\n";
}
// Stub for the senior function.
void senior(int months)
{
cout << "The function senior was called with " << months;
cout << " as its argument.\n";
}
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