Chapter 6 Functions

1
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 int main()
  is called the function header.

4
Figure 6-1
5
Calling a Function

• Function Header
• void displayMessage()
• Function Call
• displayMessage()

6
Program 6-1

• include ltiostreamgt
• using namespace std
• // Definition of function displayMessage.
• // This function displays a greeting.
• void displayMessage()
• cout ltlt "Hello from the function
  displayMessage.\n"
•  
• int main()
• cout ltlt "Hello from main.\n"
• displayMessage()
• cout ltlt "Back in function main again.\n"
• return 0

7
Program Output

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

8
Figure 6-2
void displayMessage() cout ltlt Hello from the
function displayMessage.\n
int main() cout ltlt Hello from
main.\n displayMessage() cout ltlt Back in
function main again.\n return 0
9
Program 6-2

• //The function displayMessage is repeatedly
  called from a loop
• include ltiostreamgt
• using namespace std
•  
• void displayMessage()
• cout ltlt "Hello from the function
  displayMessage.\n"
•  
• int main()
• cout ltlt "Hello from main.\n"
• for (int count 0 count lt 5 count)
• displayMessage() // Call displayMessage
• cout ltlt "Back in function main again.\n"
• return 0

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 ltiostreamgt
• using namespace std
• // Definition of function first.
• // This function displays a message.
•  
• void first()
• cout ltlt "I am now inside the function first.\n"

12
 Program continues

• // Definition of function second. This function
  displays a message.
• void second()
• cout ltlt "I am now inside the function
  second.\n"
•  
• int main()
• cout ltlt "I am starting in function main.\n"
• first() // Call function first
• second() // Call function second
• cout ltlt "Back in function main again.\n"return
  0

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 6-3
void first() cout ltlt I am now inside
function first.\n
void second() cout ltlt I am now inside
function second.\n
int main() cout ltlt I am starting in
function main.\n first() second()
cout ltlt Back in function main again.\n
return 0
15
Program 6-4

• // This program has three functions main, deep,
  and deeper
•  
• include ltiostreamgt
• using namespace std
• // Definition of function deeper.
• // This function displays a message.
•  
• void deeper()
• cout ltlt "I am now inside the function
  deeper.\n"

16
 Program continues

• // Definition of function deep.
• // This function calls the function deeper.
•  void deep()
• cout ltlt "I am now inside the function deep.\n"
• deeper() // Call function deeper
• cout ltlt "Now I am back in deep.\n"
•  int main()
• cout ltlt "I am starting in function main.\n"
• deep() // Call function deep
• cout ltlt "Back in function main again.\n"
• return 0

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 6-4
void deep() cout ltlt I am now inside
function deep.\n deeper() cout ltlt Now I
am back in deep.\n
void deeper() cout ltlt I am now inside
function deeper.\n
int main() cout ltlt I am starting in
function main.\n deep() cout ltlt Back in
function main again.\n return 0
19
6.3 Sending Information Into a Function

• When a function is called, the program may send
  values into the function.

20
Program 6-5

•  include ltiostreamgt
• using namespace std
• // Definition of function displayValue.
• // It uses an integer parameter whose value is
  displayed.
• void displayValue(int num)
• cout ltlt "The value is " ltlt num ltlt endl
•  
• int main()
• cout ltlt "I am passing 5 to displayValue.\n"
• displayValue(5) // Call displayValue with
  argument 5
• cout ltlt "Now I am back in main.\n"
• return 0

21
Program Output

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

22
Figure 6-5
displayValue(5)
void displayValue(int num) cout ltlt The
value is ltlt num ltlt endl
23
Program 6-6

• // This program demonstrates a function with a
  parameter.
• include ltiostreamgt
• using namespace std
•  
• // Definition of function displayValue.
• // It uses an integer parameter whose value is
  displayed.
• void displayValue(int num)
• cout ltlt "The value is " ltlt num ltlt endl

24
Program continues

• int main()
• cout ltlt "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 ltlt "Now I am back in main.\n"
• return 0

25
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.

26
Program 6-7

• // This program demonstrates a function with
  three parameters.
•  
• include ltiostreamgt
• using namespace std
• // Definition of function showSum.
• // It uses three integer parameters. Their sum is
  displayed.
• void showSum(int num1, int num2, int num3)
• cout ltlt (num1 num2 num3) ltlt endl

27
 Program continues

• int main()
• int value1, value2, value3
•   cout ltlt "Enter three integers and I will
  display "
• cout ltlt "their sum "
• cin gtgt value1 gtgt value2 gtgt value3
• showSum(value1, value2, value3) // Call showSum
  with // 3
  arguments
• return 0

28
Program Output with Example Input

• Enter three integers and I will display their
  sum 4 8 7 Enter
• 19

29
Figure 6-6
showSum(value1, value2, value3)
void showSum(int num1, int num2, int num3)
cout ltlt num1 num2 num3 ltlt endl
30
6.4 Changing the value of a Parameter

• When an argument is passed into a parameter, only
  a copy of the arguments value is passed.
  Changes to the parameter do not affect the
  original argument. This is called passed by
  value.

31
Program 6-8

• // This program demonstrates that changes to a
  function parameter
• // have no effect on the original argument.
•  include ltiostreamgt
•  using namespace std
• // 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 ltlt "In changeThem the value of i is changed
  to "
• cout ltlt i ltlt endl
• cout ltlt "and the value of f is changed to " ltlt f
  ltlt endl

32
  Program continues

• int main()
• int whole 12
• float real 3.5
•   cout ltlt "In main the value of whole is " ltlt
  whole ltlt endl
• cout ltlt "and the value of real is " ltlt real ltlt
  endl
• changeThem(whole, real) // Call changeThem with
  2 arguments
• cout ltlt "Now back in main again, the value of "
• cout ltlt "whole is " ltlt whole ltlt endl
• cout ltlt "and the value of real is " ltlt real ltlt
  endl
• return 0

33
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

34
Figure 6-7
35
6.5 Function Prototypes

• A function prototype eliminates the need to place
  a function definition before all calls to the
  function.
• You may optionally list the parameter variable
  names in a function prototype, although the
  compiler only needs the types.
• You must place either the function definition or
  function prototype ahead of all calls to the
  function. Otherwise the program will not compile.

36
Program 6-9

• // This program uses a function prototype for
  showSum
•  
• include ltiostreamgt
• using namespace std
• void showSum(int, int, int) // Function
  prototype
•  
• int main()
• int value1, value2, value3
• cout ltlt "Enter three integers and I will display
  "
• cout ltlt "their sum "
• cin gtgt value1 gtgt value2 gtgt value3
• showSum(value1, value2, value3)
• return 0

37
 Program continues

• // Definition of function showSum.
• // It uses three integer parameters. Their sum is
• // displayed.
•  
• void showSum(int num1, int num2, int num3)
• cout ltlt num1 num2 num3 ltlt endl
•  

38
Program 6-10

• // This program has three functions main, first,
  and second.
•  
• include ltiostreamgt
•  using namespace std
• // Function prototypes
• void first()
• void second()
•  
• int main()
• cout ltlt "I am starting in function main.\n"
• first()
• second()
• cout ltlt "Back in function main again.\n"
• return 0

39
Program continues

• // Definition of function first
• void first()
• cout ltlt "I am now inside the function first.\n"
•  
• // Definition of function second
• void second()
• cout ltlt "I am now inside the function
  second.\n"

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 6-11

• // This is a menu-driven program that makes a
  function call
• // for each selection the user makes.
• include ltiostreamgt
• using namespace std
• // Function Prototypes
• void adult(int)
• void child(int)
• void senior(int)
•  
• int main()
• int months, choice

42
 Program continues

• cout.setf(iosfixed iosshowpoint)
• cout.precision(2)
•   do
• cout ltlt "\n\t\tHealth Club Membership
  Menu\n\n"
• cout ltlt "1. Standard adult Membership\n"
• cout ltlt "2. child Membership\n"
• cout ltlt "3. senior Citizen Membership\n"
• cout ltlt "4. Quit the Program\n\n"
• cout ltlt "Enter your choice "
• cin gtgt choice

43
Program continues

• if (choice ! 4)
• cout ltlt "For how many months? "
• cin gtgt months
• switch (choice)
• case 1 adult(months)
• break
• case 2 child(months)
• break
• case 3 senior(months)
• break
• case 4 cout ltlt "Thanks for using this "
• cout ltlt "program.\n"
• break

44
Program continues

• default cout ltlt "The valid choices are 1-4. "
• cout ltlt "Try again.\n"
• while (choice ! 4)
• return 0
•  
• // 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 ltlt "The total charges are "
• cout ltlt (mon 40.0) ltlt 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 ltlt "The total charges are "
• cout ltlt (mon 20.0) ltlt 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 ltlt "The total charges are "
• cout ltlt (mon 30.0) ltlt endl

47
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.

48
6.7 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.

49
Program 6-12

• // This program shows that variables declared in
  a function
• // are hidden from other functions.
• include ltiostreamgt
• using namespace std
• void func() // Function prototype
•  
• int main()
• int num 1
• cout ltlt "In main, num is " ltlt num ltlt endl
• func()
• cout ltlt "Back in main, num is still " ltlt num ltlt
  endl
• return 0

50
 Program continues

• // Definition of function func.
• // It has a local variable, num, whose initial
  value, 20,
• // is displayed.
•  
• void func()
• int num 20
•   cout ltlt "In func, num is " ltlt num ltlt endl
•  

51
Program Output

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

52
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.
53
Program 6-13

• // This program shows that a global variable is
  visible
• // to all the functions that appear in a program
  after
• // the variable's declaration.
•  
• include ltiostreamgt
• using namespace std
• void func() // Function prototype
• int num 2 // Global variable
•  
• int main()
• cout ltlt "In main, num is " ltlt num ltlt endl
• func()
• cout ltlt "Back in main, num is " ltlt num ltlt endl
• return 0

54
 Program continues

• // Definition of function func.
• // func changes the value of the global variable
  num.
• void func()
• cout ltlt "In func, num is " ltlt num ltlt endl
• num 50
• cout ltlt "But, it is now changed to " ltlt num ltlt
  endl
•  

55
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

56
Program 6-14

• // This program shows that a global variable is
  visible
• // to all the functions that appear in a program
  after
• // the variable's declaration.
• include ltiostreamgt
• using namespace std 
• void func() // Function prototype
•  
• int main()
• cout ltlt "In main, num is not visible!\n"
• func()
• cout ltlt "Back in main, num still isn't
  visible!\n"
• return 0

57
 Program continues

• int num 2 // Global variable
• // Definition of function func
• // func changes the value of the global variable
  num.
• void func()
• cout ltlt "In func, num is " ltlt num ltlt endl
• num 50
• cout ltlt "But, it is now changed to " ltlt num ltlt
  endl

58
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!

59
Program 6-15

• // This program has an uninitialized global
  variable.
• include ltiostreamgt
• using namespace std
• int globalNum // Global variable. Automatically
  set to zero.
•  
• int main()
• cout ltlt "globalNum is " ltlt globalNum ltlt endl
• return 0

60
Program Output

• globalNum is 0

61
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.

62
Program 6-16

• // This program shows that when a local variable
  has the
• // same name as a global variable, the function
  only sees
• // the local variable.
•  
• include ltiostreamgt
• using namespace std
• // Function prototypes
• void texas()
• void arkansas()
•  
• int cows 10

63
 Program continues

• int main()
• cout ltlt "There are " ltlt cows ltlt " cows in
  main.\n"
• texas()
• arkansas()
• cout ltlt "Back in main, there are " ltlt cows ltlt "
  cows.\n"
• return 0
•  
• // Definition of function texas.
• // The local variable cows is set to 100.
•  void texas()
• int cows 100
•  
• cout ltlt "There are " ltlt cows ltlt " cows in
  texas.\n"

64
 Program continues

• // Definition of function arkansas.
• // The local variable cows is set to 50.
•  
• void arkansas()
• int cows 50
•   cout ltlt "There are " ltlt cows ltlt " cows in
  arkansas.\n"
•  

65
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.
•  

66
Program 6-17

• // 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 ltiostreamgt
• using namespace std 
• void ringUpSale() // Function prototype
•  
• // Global Variables
• const float taxRate 0.06
• float tax, sale, total
•  
• int main()
• char again

67
 Program continues

• cout.precision(2)
• cout.setf(iosfixed iosshowpoint)
• do
• ringUpSale()
• cout ltlt "Is there another item to be purchased?
  "
• cin gtgt again
• while (again 'y' again 'Y')
• tax sale taxRate
• total sale tax
• cout ltlt "The tax for this sale is " ltlt tax ltlt
  endl
• cout ltlt "The total is " ltlt total ltlt endl
• return 0

68
 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()
• int qty
• float unitPrice, tax, thisSale, subTotal
•  
• cout ltlt "Quantity "
• cin gtgt qty
• cout ltlt "Unit price "
• cin gtgt unitPrice
• thisSale qty unitPrice // Get the total
  unit price

69
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 ltlt "Price for these items " ltlt thisSale ltlt
  endl
• cout ltlt "tax for these items " ltlt tax ltlt endl
• cout ltlt "subTotal for these items " ltlt subTotal
  ltlt endl

70
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

71
Be Careful With Global Variables

• It is tempting to make all your variables global.
  But dont do it!
• Using global variables can cause problems.
• It is harder to debug a program that uses global
  variables

72
6.8 Static Local Variables

• If a function is called more than once in a
  program, the values stored in the functions
  local variables do not persist between function
  calls.
• To get a variable to keep its value even after
  the function ends, you must create static
  variables

73
Program 6-18

• // This program shows that local variables do not
  retain
• // their values between function calls.
•  
• include ltiostreamgt
• using namespace std
• // Function prototype
• void showLocal()
•  
• int main()
• showLocal()
• showLocal()
• return 0

74
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()
• int localNum 5 // Local variable
•  
• cout ltlt "localNum is " ltlt localNum ltlt endl
• localNum 99

75
Program Output

• localNum is 5
• localNum is 5

76
Program 6-19

• //This program uses a static local variable.
• include ltiostreamgt
• void showStatic() // Function prototype
• int main()
• for (int count 0 count lt 5 count)
• showStatic()
• return 0
• // Definition of function showStatic.
• void showStatic()
• static int statNum
• cout ltlt "statNum is " ltlt statNum ltlt endl
• statNum

77
Program Output

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

78
Program 6-20

• // This program shows that a static local
  variable is only
• // initialized once.
• include ltiostreamgt
• using namespace std
• void showStatic() // Function prototype
• int main()
• for (int count 0 count lt 5 count)
• showStatic()return 0

79
 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 ltlt "statNum is " ltlt statNum ltlt endl
• statNum

80
Program Output

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

81
6.9 Default Arguments

• Default arguments are passed to parameters
  automatically if no argument is provided in the
  function call.
• A functions default arguments should be assigned
  in the earliest occurrence of the function name.
  This will usually mean the function prototype.

82
Program 6-21

• // This program demonstrates default function
  arguments.
• include ltiostreamgt
• using namespace std
• // Function prototype with default arguments
• void displayStars(int 10, int 1)
•  
• int main()
• displayStars()
• cout ltlt endl
• displayStars(5)
• cout ltlt endl
• displayStars(7, 3)
• return 0

83
 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 lt rows down)
• for (int across 0 across lt cols across)
• cout ltlt ""
• cout ltlt endl
•  

84
Program Output

•  
•  

85
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.

86
6.10 Using Reference Variables as Parameters

• When used as parameters, reference variables
  allow a function to access the parameters
  original argument, changes to the parameter are
  also made to the argument.

87
Example

• void doubleNum(int refVar)
• refVar 2
• // The variable refVar is called
• // a reference to an int

88
Program 6-22

• // This program uses a reference variable as a
  function
• // parameter.
• include ltiostreamgt
• // Function prototype. The parameter is a
  reference variable.
• void doubleNum(int )
•  
• int main()
• int value 4
•   cout ltlt "In main, value is " ltlt value ltlt endl
• cout ltlt "Now calling doubleNum..." ltlt endl
• doubleNum(value)
• cout ltlt "Now back in main. value is " ltlt value
  ltlt endl
• return 0

89
 Program continues

• // Definition of doubleNum.
• // The parameter refVar is a reference variable.
  The value
• // in refVar is doubled.
•  
• void doubleNum (int refVar)
• refVar 2
•  

90
Program Output

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

91
Program 6-23

• // This program uses reference variables as
  function
• // parameters.
• include ltiostreamgt
• // Function prototypes. Both functions use
  reference variables
• // as parameters
• void doubleNum(int )
• void getNum(int )
•  
• int main()
• int value
• getNum(value)
• doubleNum(value)
• cout ltlt "That value doubled is " ltlt value ltlt
  endl
• return 0

92
 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 ltlt "Enter a number "
• cin gtgt userNum

93
 Program continues

• // Definition of doubleNum.
• // The parameter refVar is a reference variable.
  The value
• // in refVar is doubled.
•  
• void doubleNum (int refVar)
• refVar 2

94
Program Output with Example Input

• Enter a number 12 Enter
• That value doubled is 24
•  

95
Reference Argument Warning

• Dont get carried away with using reference
  variables as function parameters. Any time you
  allow a function to alter a variable thats
  outside the function, you are creating potential
  debugging problems. Reference variables should
  only be used as parameters when the situation
  demands them.

96
6.11 The return Statement

• The return statement causes a function to end.

97
Program 6-24

• // This program demonstrates a function with a
  return statement.
• include ltiostreamgt
• using namespace std 
• // Function prototype
• void halfway()
•  
• int main()
• cout ltlt "In main, calling halfway...\n"
• halfway()
• cout ltlt "Now back in main.\n"
• return 0

98
 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()
• cout ltlt "In halfway now.\n"
• return
• cout ltlt"Will you ever see this message?\n"

99
Program Output

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

100
Program 6-25

• // This program uses a function to perform
  division. If division
• // by zero is detected, the function returns.
• include ltiostreamgt
• using namespace std
• // Function prototype.
• void divide(float, float)
•  
• int main()
• float num1, num2
•  
• cout ltlt "Enter two numbers and I will divide the
  first\n"
• cout ltlt "number by the second number "
• cin gtgt num1 gtgt num2
• divide(num1, num2)
• return 0

101
 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 ltlt "Sorry, I cannot divide by zero.\n"
• return
• cout ltlt "The quotient is " ltlt (arg1 / arg2) ltlt
  endl

102
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.

103
6.12 Returning a value From a Function

• A function may send a value back to the part of
  the program that called the function.

104
Figure 6-10
105
Program 6-26

• // This program uses a function that returns a
  value.
• include ltiostreamgt
• using namespace std 
• //Function prototype
• int square(int)
• int main()
• int value, result
• cout ltlt "Enter a number and I will square it "
• cin gtgt value
• result square(value)
• cout ltlt value ltlt " squared is " ltlt result ltlt
  endl
• return 0

106
 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

107
Program Output with Example Input

• Enter a number and I will square it 20 Enter
• 20 squared is 400

108
Figure 6-11
result square(value)
20
int square(int number) return number
number
109
6.13 Returning Boolean Values

• Function may return true or false values.

110
Program 6-28

• // This program uses a function that returns true
  or false.
• include ltiostreamgt
• using namespace std
• // Function prototype
• bool isEven(int)
• int main()
• int val
•  
• cout ltlt "Enter an integer and I will tell you "
• cout ltlt "if it is even or odd "
• cin gtgt val
• if (isEven(val))
• cout ltlt val ltlt " is even.\n"
• else
• cout ltlt val ltlt " is odd.\n"
• return 0

111
 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)
• if (number 2)
• return false // The number is odd if there's a
  remainder.
• else
• return true // Otherwise, the number is even.

112
Program Output

• Enter an integer and I will tell you if it is
  even or odd 5 Enter
• 5 is odd.
•  

113
6.14 Overloaded Functions

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

114
Program 6-29

• include ltiostreamgt
• using namespace std
• // Function prototypes
• int square(int)
• float square(float)
• int main()
• int userInt
• float userFloat
•  
• cout.precision(2)
• cout ltlt "Enter an integer and a floating-point
  value "
• cin gtgt userInt gtgt userFloat
• cout ltlt "Here are their squares "
• cout ltlt square(userInt) ltlt " and " ltlt
  square(userFloat)
• return 0

115
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

116
Program Output with Example Input

• Enter an integer and floating-point value 12 4.2
  Enter
• Here are their squares 144 and 17.64

117
6.15 The exit() Function

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

118
Program 6-31

• // This program shows how the exit function
  causes a program
• // to stop executing.
•  
• include ltiostreamgt
• include ltcstdlibgt // For exit
• using namespace std
• void function() // Function prototype
•  
• int main()
• function()
• return 0

119
 Program continues

• // This function simply demonstrates that exit
  can be used
• // to terminate a program from a function other
  than main.
• void function()
• cout ltlt "This program terminates with the exit
  function.\n"
• cout ltlt "Bye!\n"
• exit(0)
• cout ltlt "This message will never be
  displayed\n"
• cout ltlt "because the program has already
  terminated.\n"

120
Program Output

• This program terminates with the exit function.
• Bye!

121
Program 6-32

• // This program demonstrates the exit function.
• include ltiostreamgt
• include ltcstdlibgt // For exit
• include ltcctypegt // For toupper
• using namespace std 
• int main()
• char response
•  
• cout ltlt "This program terminates with the exit
  function.\n"
• cout ltlt "Enter S to terminate with the
  EXIT_SUCCESS code\n"
• cout ltlt "or f to terminate with the EXIT_FAILURE
  code "
• cin gtgt response

122
 Program continues

• if (toupper(response) 'S')
• cout ltlt "Exiting with EXIT_SUCCESS.\n"
• exit(EXIT_SUCCESS)
• else
• cout ltlt "Exiting with EXIT_FAILURE.\n"
• exit(EXIT_FAILURE)
• return 0

123
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.

124
6.16 Focus on Software Engineering Multi-File
Programs

• Large programs may be broken into several files.
  The files are compiled separately and linked into
  one executable.

125
Strategy for Creating a Multi-File Program

• Group all specialized functions that perform
  similar tasks into the same files. For example,
  a file might be created for functions that
  perform mathematical operations. Another file
  might contain functions for user input and
  output.
• Group function main and all functions that play a
  primary role into one file.
• Create a separate header file for each file that
  contains function definitions. The header files
  contain prototypes for each function.

126
Figure 6-12
File 1 bank.cpp
File 3 loans.cpp
Contains main and all primary functions.
Contains all functions for processing loans.
File 2 bank.h
File 4 loans.h
Contains prototypes for functions in bank.cpp
Contains prototypes for functions in loans.cpp
File 5 savings.cpp
File 7 checking.cpp
Contains all functions for processing savings
accounts.
Contains all functions for processing checking
accounts.
File 6 savings.h
File 8 checking.h
Contains prototypes for functions in savings.cpp
Contains prototypes for functions in checking.cpp
127
6.17 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.

128

• // Stub for the adult function.
• void adult(int months)
• cout ltlt "The function adult was called with " ltlt
  months
• cout ltlt " as its argument.\n"
• // Stub for the child function.
• void child(int months)
• cout ltlt "The function child was called with " ltlt
  months
• cout ltlt " as its argument.\n"
• // Stub for the senior function.
• void senior(int months)
• cout ltlt "The function senior was called with "
  ltlt months
• cout ltlt " as its argument.\n"