Chapter 6 Functions

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Transcript Chapter 6 Functions

Chapter 6 Functions

Starting Out with C++, 3 rd Edition

6.1 Focus on Software Engineering: Breaking Up Your Programs

• Programs may be broken up into many manageable functions.

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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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Figure 6-1

Return Type Parameter List (This one is empty) Name Body void main(void) { cout << “Hello World\n”; } 4

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Calling a Function

• Function Header void displayMessage() • Function Call displayMessage(); 5

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Program 6-1

#include //****************************************** // 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"; } 6

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Program Output

Hello from main.

Hello from the function displayMessage.

Back in function main again.

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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”; } 8

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Program 6-2

//The function displayMessage is repeatedly called from a loop #include //****************************************** // 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"; } 9

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Program Output

Hello from main.

Hello from the function displayMessage.

Back in function main again.

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Program 6-3

// This program has three functions: main, first, and second.

#include //************************************* // Definition of function first. * // This function displays a message. * //************************************* void first(void) { cout << "I am now inside the function first.\n"; } 11

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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 first second(); // Call function second cout << "Back in function main again.\n"; } 12

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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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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” } 14

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Program 6-4

// This program has three functions: main, deep, and deeper #include //************************************** // Definition of function deeper. * // This function displays a message. * //************************************** void deeper(void) { cout << "I am now inside the function deeper.\n"; } 15

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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"; } 16

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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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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” } 18

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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); 19

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Program 6-5

// This program has three functions: main, first, and second.

#include // Function Prototypes void 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

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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”; } 21

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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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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; } 23

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Program 6-6

// This program demonstrates a function with a parameter.

#include // 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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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; } 25

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Program Output

I am passing 5 to displayValue.

The value is 5 Now I am back in main.

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Figure 6-5

displayValue(5); void displayValue(int num) { cout << “The value is “ << num << endl; } 27

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Program 6-7

// This program demonstrates a function with a parameter.

#include // 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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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; } 29

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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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Program 6-8

// This program demonstrates a function with three parameters.

#include // 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 31

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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; } 32

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Program Output with Example Input

Enter three integers and I will display their sum:

4 8 7 [Enter]

19 33

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Figure 6-6

showSum(value1, value2, value3); void showSum(int num1, int num2, int num3) { cout << num1 + num2 + num3 << endl; } 34

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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.” 35

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Program 6-9

// This program demonstrates that changes to a function parameter // have no effect on the original argument.

#include // 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; } 36

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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; } 37

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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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Figure 6-7

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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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Program 6-10

// This is a menu-driven program that makes a function call // for each selection the user makes.

#include // Function Prototypes void adult(int); void child(int); void senior(int); void main(void) { int choice, months; 41

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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; 42

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Program continues

if (choice != 4) { cout << "For how many months? "; cin >> months; } switch (choice) { case 1: adult(months); break; case 2: case 3: case 4: child(months); break; senior(months); break; cout << "Thanks for using this "; cout << "program.\n"; break; 43

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}

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; } 44

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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; } 45

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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; } 46

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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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6.7 The return Statement

• The return statement causes a function to end immediately.

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Program 6-11

// This program demonstrates a function with a return statement.

#include // Function prototype void halfway(void); void main(void) { cout << "In main, calling halfway...\n"; halfway(); cout << "Now back in main.\n"; } 49

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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"; } 50

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Program Output In main, calling halfway...

In halfway now.

Now back in main.

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Program 6-12

// This program uses a function to perform division. If division // by zero is detected, the function returns.

#include // 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); 52

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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; } 53

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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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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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Figure 6-10

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Program 6-13

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

#include //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; } 57

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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; } 58

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Program Output with Example Input

Enter a number and I will square it:

20 [Enter]

20 squared is 400 59

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Figure 6-11

result = square(value);

int square(int number) { return number * number; } 60

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6.9 Returning Boolean Values

• Function may return true or false values.

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Program 6-15

// This program uses a function that returns true or false.

#include // 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"; 62

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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; 63

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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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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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Program 6-16

// This program shows that variables declared in a function // are hidden from other functions.

#include 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; } 66

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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; } 67

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Program Output

In main, num is 1 In func, num is 20 Back in main, num is still 1 68

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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 .

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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 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; } 70

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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; } 71

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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 72

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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 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"; } 73

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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; } 74

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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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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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Program 6-19

// This program has an uninitialized global variable.

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

void main(void) { cout << "globalNum is " << globalNum << endl; } 77

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globalNum is 0

Program Output

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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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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 // 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"; } 80

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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"; 81

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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"; 82

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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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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 void ringUpSale(void); // Function prototype // Global Variables const float taxRate = 0.06; float tax, sale, total; void main(void) { char again; 84

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}

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; 85

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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 86

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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; 87

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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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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 89

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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 90

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Program 6-22

// This program shows that local variables do not retain // their values between function calls.

#include // Function prototype void showLocal(void); void main(void) { showLocal(); showLocal(); } 91

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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; 92

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Program Output localNum is 5 localNum is 5 93

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Program 6-23

//This program uses a static local variable.

#include 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++; 94

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Program Output

statNum is 0 statNum is 1 statNum is 2 statNum is 3 statNum is 4 95

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Program 6-24

// This program shows that a static local variable is only // initialized once.

#include void showStatic(void); // Function prototype void main(void) { for (int count = 0; count < 5; count++) showStatic(); } 96

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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++; 97

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Program Output statNum is 5 statNum is 6 statNum is 7 statNum is 8 statNum is 9 98

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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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Program 6-25

// This program demonstrates default function arguments.

#include // Function prototype with default arguments void displayStars(int = 10, int = 1); void main(void) { displayStars(); cout << endl; displayStars(5); cout << endl; displayStars(7, 3); } 100

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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; } } 101

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Program Output ********** ***** ******* ******* ******* 102

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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.

103

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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.

104

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Example:

void doubleNum(int &refVar) { refVar *= 2; } // The variable refVar is called // “a reference to an int” 105

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Program 6-26

// This program uses a reference variable as a function // parameter.

#include // 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; } 106

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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; } 107

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Program Output In main, value is 4 Now calling doubleNum...

Now back in main. value is 8 108

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Program 6-27

// This program uses reference variables as function // parameters.

#include // 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; } 109

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//************************************************************* // 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; } 110

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Program Output with Example Input Enter a number:

12 [Enter]

That value doubled is 24 112

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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 // 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); 115

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// 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

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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 // 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”; 118

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} { 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; } 119

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//*********************************************************** // 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’); } 120

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//*********************************************************** // 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; } 121

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//*********************************************************** // 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; } 122

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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 #include // For exit void function(void); // Function prototype void main(void) { function(); } 125

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//*********************************************************** // 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"; } 126

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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 #include // 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; 128

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} if (response == 'S') { cout << "Exiting with EXIT_SUCCESS.\n"; exit(EXIT_SUCCESS); } else { cout << "Exiting with EXIT_FAILURE.\n"; exit(EXIT_FAILURE); } 129

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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"; } 132

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