Starting Out with C++, 3 rd Edition 1 Chapter 6 Functions

1

Starting Out with C++, 3rd Edition

Chapter 6 Functions

2


6.1 Focus on Software Engineering: Breaking Up Your Programs

• Programs may be broken up into many manageable functions.

3


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.

4


Figure 6-1

void main(void){

cout << “Hello World\n”;}

Return Type

Name

Parameter List (This one is empty)

Body

5


Calling a Function

• Function Header

void displayMessage()• Function Call

displayMessage();

6


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";

}

7


Program Output

Hello from main.Hello from the function displayMessage.Back in function main again.

8


Figure 6-2

void main(void){

cout << “Hello from main.\n”;displayMessage();cout << “Back in function main again.\n”;

}

void displayMessage(){

cout << “Hello from the function displayMessage.\n”;}

9


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 displayMessagecout << "Back in function main again.\n";

}

10


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.

11


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";

}

12


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 starting in function main.\n";first(); // Call function firstsecond(); // Call function secondcout << "Back in function main again.\n";

}

13


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.

14


Figure 6-3void 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”}

15


Program 6-4// This program has three functions: main, deep, and deeper


//**************************************

// Definition of function deeper. *

// This function displays a message. *

//**************************************

void deeper(void)

{

cout << "I am now inside the function deeper.\n";

}

16


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 deepercout << "Now I am back in deep.\n";

}void main(void){

cout << "I am starting in function main.\n";deep(); // Call function deepcout << "Back in function main again.\n";

}

17


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.

18


Figure 6-4void 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”}

19


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);

20


Program 6-5// This program has three functions: main, first, and second.


// Function Prototypesvoid first(void);void second(void); void main(void){

cout << "I am starting in function main.\n"; first(); // Call function first second(); // Call function second

cout << “Back in function main again.\n";}

Program Continues on next slide

21


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”;}

22


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.

23


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;}

24


Program 6-6 // This program demonstrates a function with a parameter.


// 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

25


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;

}

26


Program Output

I am passing 5 to displayValue.The value is 5Now I am back in main.

27


Figure 6-5

displayValue(5);

void displayValue(int num){ cout << “The value is “ << num << endl;}

28


Program 6-7// This program demonstrates a function with a parameter.#include <iostream.h>

// Function Prototypevoid displayValue(int);

void main(void){

cout << "I am passing several values to displayValue.\n";displayValue(5); // Call displayValue with argument 5displayValue(10); // Call displayValue with argument 10displayValue(2); // Call displayValue with argument 2displayValue(16); // Call displayValue with argument 16cout << "Now I am back in main.\n";

}

Program continues on next slide

29


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;

}

30


Program Output

I am passing several values to displayValue.The value is 5The value is 10The value is 2The value is 16Now I am back in main.

31


Program 6-8// This program demonstrates a function with three parameters. #include <iostream.h>

// Function prototypevoid 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

}

32


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;

}

33


Program Output with Example Input

Enter three integers and I will display their sum: 4 8 7 [Enter]

19

34


Figure 6-6showSum(value1, value2, value3);

void showSum(int num1, int num2, int num3){ cout << num1 + num2 + num3 << endl;}

35


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.”

36


Program 6-9// This program demonstrates that changes to a function parameter// have no effect on the original argument.#include <iostream.h>

// Function Prototypevoid 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 argumentscout << "Now back in main again, the value of ";cout << "whole is " << whole << endl; cout << "and the value of real is " << real << endl;

}

37


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;

}

38


Program Output

In main the value of whole is 12 and the value of real is 3.5In changeThem the value of i is changed to 100 and the value of f is changed to 27.5Now back in main again, the value of whole is 12and the value of real is 3.5

39


Figure 6-7

40


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.

41


Program 6-10// This is a menu-driven program that makes a function call

// for each selection the user makes.


// Function Prototypes

void adult(int);

void child(int);

void senior(int);

void main(void)

{

int choice, months;

42


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;

43


Program continuesif (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;

44


Program continuesdefault: 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;}

45


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;

}

46


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;

}

47


Program Output with Example Input Health Club Membership Menu

1. Standard adult Membership2. child Membership3. senior Citizen Membership4. Quit the Program

Enter your choice: 1 For how many months 12The total charges are $480.00 Health Club Membership Menu

1. Standard adult Membership2. child Membership3. senior Citizen Membership4. Quit the Program

Enter your choice: 4Thanks for using this program.

48


6.7 The return Statement

• The return statement causes a function to end immediately.

49


Program 6-11// This program demonstrates a function with a return

statement.

#include <iostream.h> // Function prototypevoid halfway(void); void main(void){cout << "In main, calling halfway...\n";halfway();cout << "Now back in main.\n";

}

50


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";

}

51


Program Output

In main, calling halfway...In halfway now.Now back in main.

52


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);

}

53


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;

}

54



Enter two numbers and I will divide the firstnumber by the second number: 12 0 [Enter]Sorry, I cannot divide by zero.

55


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.

56


Figure 6-10

57


Program 6-13

// This program uses a function that returns a value.


//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;

}

58


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;

}

59



Enter a number and I will square it: 20 [Enter]20 squared is 400

60


Figure 6-11

result = square(value);

int square(int number){


}

20

61


6.9 Returning Boolean Values

• Function may return true or false values.

62


Program 6-15// This program uses a function that returns true or false.


// 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";

}

63


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;

}

64


Program Output

Enter an integer and I will tell you if it is even or odd: 5 [Enter]

5 is odd.

65


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.

66


Program 6-16

// This program shows that variables declared in a function

// are hidden from other functions.


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;

}

67


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;

}

68


Program Output

In main, num is 1In func, num is 20Back in main, num is still 1

69


Figure 6-8

Function main

num = 1

Function func

num = 20

This num variable is only visible in function main.

This num variable is only visible in function func.

70


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.



int num = 2; // Global variable

void main(void)

{

cout << "In main, num is " << num << endl;

func();

cout << "Back in main, num is " << num << endl;

}

71


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;

}

72


Program Output

In main, num is 2In func, num is 2But, it is now changed to 50Back in main, num is 50

73


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.



void main(void)

{

cout << "In main, num is not visible!\n";

func();

cout << "Back in main, num still isn't visible!\n";

}

74


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;

}

75


Program Output

In main, num is not visible!In func, num is 2But, it is now changed to 50Back in main, num still isn't visible!

76


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.

77


Program 6-19// This program has an uninitialized global variable.


int globalNum; // Global variable. Automatically set to zero.

void main(void)

{

cout << "globalNum is " << globalNum << endl;

}

78


Program Output

globalNum is 0

79


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.

80


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 prototypesvoid 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";

}

81


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";

}

82


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";

}

83


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.

84


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.


void ringUpSale(void); // Function prototype

// Global Variables

const float taxRate = 0.06;

float tax, sale, total;

void main(void)

{

char again;

85


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;

}

86


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

87


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;

}

88


Program Output with Example InputQuantity: 2 [Enter]Unit Price: 20.00 [Enter]Price for these items: 40.00tax for these items: 2.40subTotal for these items: 42.40Is there another item to be purchased? y [Enter]Quantity: 3 [Enter]Unit Price: 12.00 [Enter]Price for these items: 36.00tax for these items: 2.16subTotal for these items: 38.16Is there another item to be purchased? n [Enter]The tax for this sale is 4.56The total is 80.56

89


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

90


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

91


Program 6-22

// This program shows that local variables do not retain

// their values between function calls.


// Function prototype

void showLocal(void);

void main(void)

{

showLocal();

showLocal();

}

92


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;

}

93


Program Output

localNum is 5localNum is 5

94


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++;

}

95


Program Output

statNum is 0statNum is 1statNum is 2statNum is 3statNum is 4

96


Program 6-24// This program shows that a static local variable is only

// initialized once.


void showStatic(void); // Function prototype

void main(void)

{

for (int count = 0; count < 5; count++)

showStatic();

}

97


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++;

}

98


Program Output

statNum is 5statNum is 6statNum is 7statNum is 8statNum is 9

99


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.

100


Program 6-25// This program demonstrates default function arguments.


// Function prototype with default arguments

void displayStars(int = 10, int = 1);

void main(void)

{

displayStars();

cout << endl;

displayStars(5);

cout << endl;

displayStars(7, 3);

}

101


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;}

}

102


Program Output

**********

*****

*******

*******

*******

103


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.

104


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.

105


Example:

void doubleNum(int &refVar)

{

refVar *= 2;

}

// The variable refVar is called

// “a reference to an int”

106


Program 6-26// This program uses a reference variable as a function

// parameter.


// 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;

}

107


Program continues

//************************************************************

// Definition of doubleNum. *

// The parameter refVar is a reference variable. The value *

// in refVar is doubled. *

//************************************************************

void doubleNum (int &refVar)

{

refVar *= 2;

}

108


Program Output

In main, value is 4Now calling doubleNum...Now back in main. value is 8

109


Program 6-27// This program uses reference variables as function// parameters.#include <iostream.h>

// Function prototypes. Both functions use reference variables// as parametersvoid doubleNum(int &);void getNum(int &); void main(void){

int value;getNum(value);doubleNum(value);cout << "That value doubled is " << value << endl;

}

110


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;

}

111


Program continues

//************************************************************

// Definition of doubleNum. *

// The parameter refVar is a reference variable. The value *

// in refVar is doubled. *

//************************************************************

void doubleNum (int &refVar)

{

refVar *= 2;

}

112



Enter a number: 12 [Enter]That value doubled is 24

113


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.

114


6.14 Overloaded Functions

• Two or more functions may have the same name as long as their parameter lists are different.

115


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);

}

116


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)

{


}

// 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)

{


}

117



Enter an integer and floating-point value: 12 4.2 [Enter]

Here are their squares: 144 and 17.64

118


Program 6-29// This program demonstrates overloaded functions to calculate// the gross weekly pay of hourly-paid or salaried employees.#include <iostream.h>

// Function prototypesvoid 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”;

119


Program continues getChoice(selection); switch (selection)

{ case ‘H’ : case ‘h’ : 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; case ‘S’ : case ‘s’ : cout << “What is the annual salary? “; cin >> yearly; cout << “The gross weekly pay is “; cout << calcWeeklyPay(yearly); break; }}

120


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’);}

121


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;

}

122


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;

}

123


Program Output with Example InputDo 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 InputDo 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

124


6.15 The exit() Function

• The exit() function causes a program to terminate, regardless of which function or control mechanism is executing.

125


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();}

126


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";

}

127


Program Output

This program terminates with the exit function.Bye!

128


Program 6-31// This program demonstrates the exit function.


#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;

129


Program continues

if (response == 'S')

{

cout << "Exiting with EXIT_SUCCESS.\n";

exit(EXIT_SUCCESS);

}

else

{

cout << "Exiting with EXIT_FAILURE.\n";

exit(EXIT_FAILURE);

}

}

130


Program Output with Example InputThis program terminates with the exit function.Enter S to terminate with the EXIT_SUCCESS codeor f to terminate with the EXIT_FAILURE code: s [Enter]Exiting with EXIT_SUCCESS.

Program Output With Other Example InputThis program terminates with the exit function.Enter S to terminate with the EXIT_SUCCESS codeor f to terminate with the EXIT_FAILURE code: f [Enter]Exiting with EXIT_FAILURE.

131


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.

132


// 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";

}

Documents

Starting Out with C++, 3 rd Edition 1 Chapter 6 Functions