Starting Out with C++, 3 rd Edition 1 Chapter 4. Making Decisions

1

Starting Out with C++, 3rd Edition

Chapter 4. Making Decisions

2


4.1 Relational Operators

• Relational operators allow you to compare numeric values and determine if one is greater than, less than, equal to, or not equal to another.

3


Table 4-1

Relational Operators(in Order of Precedence)

Meaning

><> =< == =!=

Greater thanLess thanGreater than or equaltoLess than or equal toEqual toNot equal to

4


Table 4-2

Expression What the Expression Means

X > YX < YX > = YX < = YX = = YX != Y

Is X greater than Y ?Is X less than Y ?Is X greater than or equal to Y ?Is X less than or equal to Y ?Is X equal to Y ?Is X not equal to Y ?

5


The Value of a Relationship

• Relational expressions are also know as a Boolean expression

• Warning! The equality operator is two equal signs together

==

6


Table 4-3

Expression Value

X < Y False, because X is not less than Y .

X > Y True, because X is greater than Y .

X > = Y True, because X is greater than or equal to Y .

X < = Y False, because X is not less than or equal to Y .

Y != X True, because Y is not equal to X .

7


Program 4-1// This program displays the values of true and false

// states.

#include <iostream.h>

void main(void)

{int trueValue, falseValue, x = 5, y = 10;

trueValue = X < Y;falseValue = Y == X;

cout << "True is " << trueValue << endl;cout << "False is " << falseValue << endl;

}Program OutputTrue is 1False is 0

8


Table 4-4 (Assume x is 10, y is 7, a and b are ints)

Statement Outcome

Z = X < Y Z is assigned 0 because X is not less than Y .

c o u t < < (X > Y ); Displays 1 because X is greater than Y .

A = X > = Y ; A is assigned 1 because X is greater than orequal to Y .

c o u t < < (X < =Y );

Displays 0 because X is not less than orequal to Y .

B = Y != X ; B is assigned 1 because Y is not equal to X .

9


4.2 The if Statement

• The if statement can cause other statements to execute only under certain conditions.

10


Program 4-2// This program averages 3 test scores#include <iostream.h>

void main(void){

int score1, score2, score3;float average;

cout << "Enter 3 test scores and I will average them: ";cin >> score1 >> score2 >> score3;average = (score1 + score2 + score3) / 3.0;cout.precision(1);cout.setf(ios::showpoint | ios::fixed);cout << "Your average is " << average << endl;if (average > 95)

cout << "Congratulations! That's a high score!\n";

}

11


Program Output with Example Input

Enter 3 test scores and I will average them: 80 90 70 [Enter]Your average is 80.0

Program Output with Other Example InputEnter 3 test scores and I will average them: 100 100 100 [Enter]Your average is 100.0

Congratulations! That's a high score!

12


Table 4-5

Statements Outcome

if (H o u rs > 4 0 ) O v e rT im e = 1 ;

Assigns 1 to O v erT im e only when H o u rs is greater than 40

if (V a lu e > 3 2 ) co u t < < " In v a lid n u m b er \n " ;

Displays the message “Invalid number” only when V a lu e is greater than 32

if (O v e rT im e = = 1 ) P ay R a te * = 2 ;

Multiplies P ay R a te by 2 only when O v erT im e is equal to 1

13


Be Careful With Semicolons

if (expression)

statement;• Notice that the semicolon comes after the

statement that gets executed if the expression is true; the semicolon does NOT follow the expression

14


Program 4-3// This program demonstrates how a misplaced semicolon// prematurely terminates an if statement.#include <iostream.h>

void main(void){

int x = 0, y = 10;cout << “x is " << x << " and y is " << y << endl;if (x > y); // misplaced semicolon!

cout << “x is greater than y\n"; // Always executed

}

Program OutputX is 0 and Y is 10

X is greater than Y

15


Programming Style and the if Statement

• The conditionally executed statement should appear on the line after the if statement.

• The conditionally executed statement should be indented one “level” from the if statement.

• Note: Each time you press the tab key, you are indenting one level.

16


Comparing Floating Point Numbers

• Round-off errors can cause problems when comparing floating point numbers with the equality operator (==)

17


Program 4-4// This program demonstrates how floating point round-off// errors can make equality comparisons unreliable. #include <iostream.h> void main(void){float result;

result = 6.0 * 0.666666; // Round-off errorif (result == 4.0)cout << "It's true!";

elsecout << "It's false!";

}

Program OutputIt's false!

18


And Now Back to Truth

• When a relational expression is true, it has the value 1.

• When a relational expression is false it has the value 0.

• An expression that has the value 0 is considered false by the if statement.

• An expression that has any value other than 0 is considered true by the if statement.

19


Not All Operators Are “Equal”

• Consider the following statement:if (x = 2) // caution here!

cout << “It is True!”;

• This statement does not determine if x is equal to 2, it assigns x the value 2, therefore, this expression will always be true because the value of the expression is 2, a non-zero value

20


Program 4-5// This program averages 3 test scores. The if statement uses// the = operator, but the == operator was intended.#include <iostream.h>

void main(void){

int score1, score2, score3;float average;

cout << "Enter 3 test scores and I will average them: ";cin >> score1 >> score2 >> score3;average = (score1 + score2 + score3) / 3.0;cout.precision(1);cout.setf(ios::showpoint | ios::fixed);cout << "Your average is " << average << endl;if (average = 100) // Wrong

cout << "Congratulations! That's a high score!\n";

}

21


Program 4-5 Output With Example Input

Program Output with Example InputEnter your 3 test scores and I will average them: 80 90 70[Enter]Your average is 80.0Congratulations! That’s a perfect score!

22


4.3 Flags

• A flag is a variable, usually a boolean or an integer, that signals when a condition exists.

• If your compiler does not support the bool data type, use int instead.

23


Program 4-6// This program averages 3 test scores. It uses the variable highScore as a flag.#include <iostream.h>

void main(void){

int score1, score2, score3;float average;bool highScore = false;

cout << "Enter your 3 test scores and I will average them: ";cin >> score1 >> score2 >> score3;average = (score1 + score2 + score3) / 3.0;if (average > 95)

highScore = true; // Set the flag variablecout.precision(1);cout.setf(ios::showpoint | ios::fixed);cout << "Your average is " << average << endl;if (highScore)

cout << "Congratulations! That's a high score!\n";\} Program Output with Example InputEnter your 3 test scores and I will average them: 100 100 100 [Enter]Your average is 100.0Congratulations! That's a high score!

24


4.4 Expanding the if Statement

• The if statement can conditionally execute a block of statement enclosed in braces.

if (expression)

{

statement;

statement;

// Place as many statements here as necessary.

}

25


Program 4-7// This program averages 3 test scores.// It uses the variable highScore as a flag.#include <iostream.h>

void main(void){

int score1, score2, score3;float average;bool highScore = false;cout << "Enter 3 test scores and I will average them: ";cin >> score1 >> score2 >> score3;average = (score1 + score2 + score3) / 3.0;if (average > 95)

highScore = true; // Set the flag variable

Program continues on next slide…

26


Program continued from previous slide

cout.precision(1);cout.setf(ios::showpoint | ios::fixed);cout << "Your average is " << average << endl;if (highScore){

cout << "Congratulations!\n";cout << "That's a high score.\n";cout << "You deserve a pat on the back!\

n";}

}

27



Enter your 3 test scores and I will average them: 100 100 100 [Enter]

Your average is 100.0Congratulations!That's a high score.

You deserve a pat on the back!

Program Output with Different Example Input

Enter your 3 test scores and I will average them: 80 90 70 [Enter]

Your average is 80.0

28


Don’t Forget the Braces!

• If you intend to execute a block of statements with an if statement, don’t forget the braces.

• Without the braces, the if statement only executes the very next statement.

29


Program 4-8// This program averages 3 test scores.// It uses the variable highScore as a flag.#include <iostream.h>

void main(void){

int score1, score2, score3;float average;bool highScore = false;

cout << "Enter 3 test scores and I will average them: ";cin >> score1 >> score2 >> score3;average = (score1 + score2 + score3) / 3.0;if (average > 95)

highScore = true; // Set the flag variable


30



cout.precision(1);cout.setf(ios::showpoint | ios::fixed);cout << "Your average is " << average << endl;

// The following if statement is // missing its braces!

if (highScore)cout << "Congratulations!\n";cout << "That's a high score.\n";cout << "You deserve a pat on the back!\

n";

}

31



Enter your 3 test scores and I will average them: 100 100 100[Enter]Your average is 100Congratulations!That’s a high score.You deserve a pat on the back!


Enter your 3 test scores and I will average them: 80 90 70[Enter]Your average is 100Congratulations!That’s a high score.You deserve a pat on the back!

32


4.5 The if/else Statement

• The if/else statement will execute one group of statements if the expression is true, or another group of statements if the expression is false.

if (expression)

statement or block of statements;

else


33


Program 4-9

// This program uses the modulus operator to determine// if a number is odd or even. If the number is evenly divided// by 2, it is an even number. A remainder indicates it is odd.#include <iostream.h>

void main(void){

int number;cout << "Enter an integer and I will tell you if it\n";cout << "is odd or even. ";cin >> number;if (number % 2 == 0)

cout << number << " is even.\n";else

cout << number << " is odd.\n";

}

34



Enter an integer and I will tell you if itis odd or even. 17 [Enter]17 is odd.

35


Program 4-10// This program asks the user for two numbers, num1 and num2.// num1 is divided by num2 and the result is displayed.// Before the division operation, however, num2 is tested// for the value 0. If it contains 0, the division does not// take place.#include <iostream.h>

void main(void){

float num1, num2, quotient;

cout << "Enter a number: ";cin >> num1;cout << "Enter another number: ";cin >> num2;


36


Program continued from previous slide.

if (num2 == 0){

cout << "Division by zero is not possible.\n";cout << "Please run the program again and enter\n";cout << "a number besides zero.\n";

}else{

quotient = num1 / num2;cout << "The quotient of " << num1 << " divided by ";cout << num2 << " is " << quotient << ".\n";

}

}

37


Program Output

(When the user enters 0 for num2)Enter a number: 10 [Enter]Enter another number: 0 [Enter]Division by zero is not possible.Please run the program again and enter

a number besides zero.

38


4.6 The if/else if Construct

The if/else if statement is a chain of if statements. The perform their tests, one after the other, until one of them is found to be true.

If (expression)


else if (expression)


// put as many else it’s as needed here

else if (expression)


39


Program 4-11// This program uses an if/else if statement to assign a// letter grade (A, B, C, D, or F) to a numeric test score.#include <iostream.h>

void main(void){

int testScore;char grade;

cout << "Enter your numeric test score and I will\n";cout << "tell you the letter grade you earned: ";cin >> testScore;


40


if (testScore < 60)grade = 'F';

else if (testScore < 70)grade = 'D';

else if (testScore < 80)grade = 'C';

else if (testScore < 90)grade = 'B';

else if (testScore <= 100)grade = 'A';

cout << "Your grade is " << grade << ".\n";

}


41



Enter your test score and I willtell you the letter grade you earned: 88 [Enter]Your grade is B.

42


Program 4-12// This program uses independent if/else statements to assign a// letter grade (A, B, C, D, or F) to a numeric test score.// Do you think it will work?#include <iostream.h>

void main(void){

int testScore;char grade;

cout << "Enter your test score and I will tell you\n";cout << "the letter grade you earned: ";cin >> testScore;


43


if (testScore < 60)grade = 'F';

if (testScore < 70)grade = 'D';

if (testScore < 80)grade = 'C';

if (testScore < 90)grade = 'B';

if (testScore <= 100)grade = 'A';

cout << "Your grade is " << grade << ".\n";

}


44



Enter your test score and I will tell youthe letter grade you earned: 40 [Enter]Your grade is A.

45


Program 4-13//This program uses an if/else if statement to//assign a letter grade ( A, B, C, D, or F )//to a numeric test score.#include<iostream.h>

void main(void){

int testScore;cout << "Enter your test score and I will tell you\n";cout << "the letter grade you earned: ";cin >> testScore;if (testScore < 60){

cout << "Your grade is F.\n"; cout << "This is a failing grade. Better see your "; cout << "instructor.\n"; } else if (testScore < 70) { cout << "Your grade is D.\n"; cout << "This is below average. You should get "; cout << "tutoring.\n"; }


46


else if (testScore < 80) { cout << "Your grade is C.\n"; cout << "This is average.\n"; } else if(testScore < 90) { cout << "Your grade is B.\n"; cout << "This is an above average grade.\n"; } else if (testScore <= 100) { cout << "Your grade is A.\n"; cout << "This is a superior grade. Good work!\n"; }}


47



Enter your test score and I will tell youthe letter grade you earned: 94 [Enter]Your grade is A.

This is a superior grade. Good work!

48


4.7 Using a Trailing else

• A trailing else, placed at the end of an if/else if statement, provides default action when none of the if’s have true expressions

49


Program 4-14// This program uses an if/else if statement to assign a// letter grade (A, B, C, D, or F) to a numeric test score.// A trailing else has been added to catch test scores > 100.


void main(void){

int testScore;

cout << "Enter your test score and I will tell you\n";cout << "the letter grade you earned: ";cin >> testScore;


50


if (testScore < 60){

cout << "Your grade is F.\n";cout << "This is a failing grade. Better see your ";cout << "instructor.\n";

}else if (testScore < 70){

cout << "Your grade is D.\n";cout << "This is below average. You should get ";cout << "tutoring.\n";

}


51


else if (testScore < 80){

cout << "Your grade is C.\n";cout << "This is average.\n";

}else if (testScore < 90){

cout << "Your grade is B.\n";cout << "This is an above average grade.\n";

}


52


else if (testScore <= 100){

cout << "Your grade is A.\n";cout << "This is a superior grade. Good work!\n";

}else // Default action{

cout << testScore << " is an invalid score.\n";cout << "Please enter scores no greater than 100.\n";

}

}


53



Enter your test score and I will tell you

the letter grade you earned: 104 [Enter]104 is an invalid score.

Please enter scores no greater than 100.

54


4.8 Focus on Software Engineering: Menus

• You can use the if/else if statement to create menu-driven programs. A menu-driven program allows the user to determine the course of action by selecting it from a list of actions.

55


Program 4-15// This program displays a menu and asks the user to make a// selection. An if/else if statement determines which item// the user has chosen.#include <iostream.h>

void main(void){

int choice, months;float charges;

cout << "\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";


56


cout << "Enter your choice: ";cin >> choice;cout.setf(ios::fixed | ios::showpoint);cout.precision(2);if (choice == 1){

cout << "\nFor how many months? ";cin >> months;charges = months * 40.00;cout << "The total charges are $" << charges <<

endl;}


57


else if (choice == 2){

cout << "\nFor how many months? ";cin >> months;charges = months * 20.00;cout << "The total charges are $" << charges << endl;

}else if (choice == 3){

cout << "\nFor how many months? ";cin >> months;charges = months * 30.00;cout << "The total charges are $" << charges << endl;

}


58


else if (choice != 4){

cout << "The valid choices are 1 through 4. Run the\n";cout << "program again and select one of those.\n";

}

}


59



Health Club Membership Menu1. Standard Adult Membership2. Child Membership3. Senior Citizen Membership4. Quit the Program

Enter your choice: 3 [Enter]For how many months? 6 [Enter]The total charges are $180.00

60


4.9 Focus on Software Engineering: Nested if Statements

• A nested if statement is an if statement in the conditionally-executed code of another if statement.

61


Program 4-16// This program demonstrates the nested if statement.#include <iostream.h>

void main(void){

char employed, recentGrad;cout << "Answer the following questions\n";cout << "with either Y for Yes or ";cout << "N for No.\n";cout << "Are you employed? ";cin >> employed;cout << "Have you graduated from college ";cout << "in the past two years? ";cin >> recentGrad;


62


if (employed == 'Y'){

if (recentGrad == 'Y') // Nested if{

cout << "You qualify for the special ";cout << "interest rate.\n";

}}

}


63



Answer the following questionswith either Y for Yes or N for No.Are you employed? Y[Enter]Have you graduated from college in the past two years? Y[Enter]You qualify for the special interest rate.

64


Program Output with Other Example Input

Answer the following questionswith either Y for Yes or N for No.Are you employed? Y[Enter]Have you graduated from college in the past two years? N[Enter]

65


4.10 Logical Operators

• Logical operators connect two or more relational expressions into one, or reverse the logic of an expression.

66


Table 4-6Operator Meaning Effect

& & AND Connects two expressions into one. Bothexpressions must be true for the overallexpression to be true.

|| OR Connects two expressions into one. One orboth expressions must be true for the overallexpression to be true. It is only necessary forone to be true, and it does not matter which.

! NOT The ! operator reverses the “truth” of anexpression. It makes a true expression false,and a false expression true.

67


Table 4-7

Expression 1 Expression 2 Expression 1 &&Expression 2

TrueFalseFalseTrue

FalseTrueFalseTrue

False (0)False (0)False (0)True (1)

68


Program 4-18// This program demonstrates the && logical operator.#include <iostream.h>

void main(void){ char employed, recentGrad;

cout << "Answer the following questions\n"; cout << "with either Y for Yes or "; cout << "N for No.\n"; cout << "Are you employed? "; cin >> employed;


69


cout << "Have you graduated from college "; cout << "in the past two years? "; cin >> recentGrad; if (employed == 'Y‘ && recentGrad == 'Y') // && Operator { cout << "You qualify for the special "; cout << "interest rate.\n"; } else { cout << "You must be employed and have \n"; cout << "graduated from college in the\n"; cout << "past two years to qualify.\n"; }

}


70



Answer the following questionswith either Y for Yes orN for No.Are you employed? Y[Enter]Have you graduated from college in the past two years? N[Enter]You must be employed and havegraduated from college in thepast two years to qualify.

71


Table 4-8

Expression 1 Expression 2 Expression 1 ||Expression 2

True False True (1)

False True True (1)

False False False (0)

True True True (1)

72


Program 4-19

// This program asks the user for their annual income and // the number of years they have been employed at their current// job. The || operator is used in a if statement that// determines if the income is at least $35,000 or their time// on the job is more than 5 years.


void main(void){

float income;int years;


73


Program continues

cout << "What is your annual income? ";cin >> income;cout << "How many years have you worked at " << "your current job? ";cin >> years;if (income >= 35000 || years > 5) // Use || logical operator

cout << "You qualify.\n";else{

cout << "You must earn at least $35,000 or have\n";cout << "been employed for more than 5 years.\n";

}

}

74



What is your annual income? 40000 [Enter]How many years have you worked at your current job? 2

[Enter]You qualify.

Program Output with Example InputWhat is your annual income? 20000 [Enter]How many years have you worked at your current job? 7

[Enter]You qualify.

75


Table 4-9

Expression !(Expression)

True False (0)

False True (1)

76


Program 4-20//This program asks the user for his annual income and //the number of years he has been employed at his current job. //The ! operator reverses the logic of the expression in the if/else statement.#include <iostream.h>

void main(void){

float income; int years;cout << "What is your annual income? ";cin >> income;cout << "How many years have you worked at " << "your current job? ";cin >> years;if (!(income >= 35000 || years > 5)) // Uses the ! Logical operator{

cout << "You must earn at least $35,000 or have\n";cout << "been employed for more than 5 years.\n";

}else

cout << "You qualify.\n";

}

77


Precedence of Logical Operators

!

&&

||

78


4.11 Checking Numeric Ranges With Logical Operators

• Logical operators are effective for determining if a number is in or out of a range.

79


4.12 Focus on Software Engineering: Validating User Input

• As long as the user of a program enters bad input, the program will produce bad output. Program should be written to filter out bad input.

80


Examples of validation:

• Numbers are check to ensure they are within a range of possible values.

• Values are check for their “reasonableness”.• Items selected from a menu or other set of choices

are check to ensure they are available options.• Variables are check for values that might cause

problems, such as division by zero.

81


4.13 More About Variable Declarations and Scope

• The scope of a variable is limited to the block in which is is declared.

• Variables declared inside a set of braces have local scope or block scope.

82


Program 4-22A//This program demonstrates late variable declaration


void main(void)

{

cout << "What is your annual income? ";

float income; // variable declaration

cin >> income;

cout << "How many years have you worked at "

<< "your current job? ";

int years; // variable declaration

cin >> years;

if (income >= 35000 || years > 5)


else

{

cout << "You must earn at least $35,000 or have\n";

cout << "been employed for more than 5 years.\n";

}

}

83


Program 4-22B

//This program demonstrates late variable declaration


void main(void)

{


float income; // variable declaration

cin >> income;



int years; // variable declaration

cin >> years;

if (income >= 35000 || years > 5)


else

{



}

}

84


Program 4-22C

//This program demonstrates late variable declaration


void main(void)

{


float income;

cin >> income;

int years;



cin >> years;

if (income >= 35000 || years > 5)


else

{



}

}

85


Program 4-23// This program demonstrates a variable declared in an inner block. #include <iostream.h> void main(void){

cout << "What is your annual income? ";float income; // variable declarationcin >> income;if (income >= 35000){

int years; // variable declarationcout << "How many years have you worked at " << "your current job? ";cin >> years;if (years > 5)



86



else

{

cout << "You must have been employed for\n";

cout << "more than 5 years to qualify.\n";

}

}

else

{

cout << "You must earn at least $35,000 to\n";

cout << "qualify.\n";

}

}

87


Variables With the Same Name

• When a block is nested inside another block, a variable declared in the inner block may have the same name as a variable declared in the outer block. The variable in the inner block takes precedence over the variable in the outer block.

88


Program 4-24// This program uses two variables with the name Number.


void main(void)

{

int number;

cout << "Enter a number greater than 0: ";

cin >> number;

if (number > 0)

{

int number;


89



cout << "Now enter another number: ";

cin >> number;

cout << "The second number you entered was ";

cout << number << endl;

}

cout << "Your first number was " << number << endl;

}

90



Enter a number greater than 0: 2 [Enter]

Now enter another number: 7[Enter]

The second number you entered was 7

Your first number was 2

91


4.14 Comparing Strings

• Use the strcmp library function to compare C-strings.

92


Program 4-25// This program illustrates that you cannot compare strings// with relational operators. Although it appears to test the// strings for equality, that is NOT what happens.#include <iostream.h>

void main(void){

char firstString[40], secondString[40]; cout << "Enter a string: ";

cin.getline(firstString, 40);cout << "Enter another string: ";cin.getline(secondString, 40);if (firstString == secondString)

cout << "You entered the same string twice.\n";else

cout << "The strings are not the same.\n";}

93



Enter a string: Alfonso [Enter]

Enter another string: Alfonso [Enter]

The strings are not the same.

94


The strcmp Function

strcmp(string1, string2); // include cstring to use

// this function

• If the two strings are identical, strcmp returns 0.

• If string1 < string 2, strcmp returns a negative number.

• If string1 > string 2, strcmp returns a positive number.

95


Program 4-26// This program correctly tests two strings for equality, with

// the strcmp function


#include <string.h>

void main(void)

{

char firstString[40], secondString[40];

cout << "Enter a string: ";

cin.getline(firstString, 40);

cout << "Enter another string: ";

cin.getline(secondString, 40);

if (strcmp(firstString, secondString) == 0)

cout << "You entered the same string twice.\n";

else

cout << "The strings are not the same.\n";

}

96


Program 4-27

// This program uses strcmp to compare the sting entered

// by the user with the valid stereo part numbers.


#include <string.h>

void main(void)

{

const float aprice = 249.0, Bprice = 299.0;

char partNum[8];

cout << "The stereo part numbers are:\n";

cout << "\tBoom Box, part number S147-29A\n";


97



cout << "\tShelf Model, part number S147-29B\n";

cout << "Enter the part number of the stereo you\n";

cout << "wish to purchase: ";

cin.width(9); // So they won't enter more than 8 char's

cin >> partNum;

cout.setf(ios::fixed || ios::showpoint);

cout.precision(2);

if (strcmp(partNum, "S147-29A") == 0) // use of strcmp

cout << "The price is $" << aprice << endl;

else if (strcmp(partNum, "S147-29B") == 0)

cout << "The price is $" << Bprice << endl;

else

cout << partNum << " is not a valid part number.\n";

}

98



The stereo part numbers are:

Boom Box, part number S14729A

Shelf Model, part number S147-29B

Enter the part number of the stereo you

wish to purchase: S147-29B [Enter]

The price is $299.00

99


Program 4-28

// This program uses the return value of strcmp to

// alphabetically sort two strings entered by the user.


#include <string.h>

void main(void)

{

char name1[30], name2[30];

cout << "Enter a name (last name first): ";

cin.getline(name1, 30);

cout << "Enter another name: ";



100



cout << "Here are the names sorted alphabetically:\n";

if (strcmp(name1, name2) < 0)

cout << name1 << endl << name2 << endl;

else if (strcmp(name1, name2) > 0)

cout << name2 << endl << name1 << endl;

else

cout << "You entered the same name twice!\n";

}

101



Enter a name (last name first): Smith, Richard [Enter]

Enter another name: Jones, John [Enter]

Here are the names sorted alphabetically

Jones, John

Smith, Richard

102


Program 4-29//This program uses strcmp to compare the string entered

//by the user with the valid stereo part numbers.

#include<iostream.h>

#include<string>

using namespace std;

void main(void)

{

const float aprice = 249.0, bprice = 299.0;

string partNum;

cout << "The stereo part numbers are:\n";

cout << "Boom box, part number S147-29A\n";

cout << "Shelf model, part number S147-29B\n";

cout << "Enter the part number of the stereo you\n";

cout << "wish to purchase: ";

cin >> partNum;


103



cout.setf(ios::fixed | ios::showpoint); cout.precision(2);

if (partNum == "S147-29A")

cout << "The price is $" << aprice << endl;

else if (partNum == "S147-29B")

cout << "The price is $" << bprice << endl;

else

cout << partNum << " is not a valid part number.";

}

104



The stereo part numbers are:

Boom box, part number S147-29A

Shelf model, part number S147-29B

Enter the part number of the stereo you

wish to purchase: S147-29A

The price is $249.00

105


4.15 The Conditional Operator

• You can use the conditional operator to create short expressions that work like if/else statements

expression ? result if true : result if false;

X < 0 ? Y = 10 : Z = 20;

106


Program 4-30// This program calculates a consultant's charges at $50 per hour,

// for a minimum of 5 hours. The ?: operator adjusts hours to 5 if less

// than 5 hours were worked.


void main(void)

{

const float payRate = 50.0;

float hours, charges;

cout << "How many hours were worked? ";

cin >> hours;

hours = hours < 5 ? 5 : hours;

charges = payRate * hours;

cout.precision(2);

cout.setf(ios::fixed | ios::showpoint);

cout << "The charges are $" << charges << endl;

}

107



How many hours were worked? 10 [Enter]

The charges are $500.00


How many hours were worked? 2 [Enter]

The charges are $250.00

108


Program 4-31// This program uses the return value of strcmp to alphabetically

// sort two strings entered by the user.


#include <string.h>

void main(void)

{

char name1[30], name2[30];

cout << "Enter a name (last name first): ";



109



cout << "Enter another name: ";


cout << "Here are the names sorted alphabetically:\n";

cout << (strcmp(name1, name2) <= 0 ? name1 : name2) << endl;

cout << (strcmp(name1, name2) > 0 ? name1 : name2) << endl;

}

110



Enter a name (last name first): Smith, Richard [Enter]

Enter another name: Jones, John [Enter]

Here are the names sorted alphabetically

Jones, John

Smith, Richard

111


4.16 The switch Statement

• The switch statement lets the value of a variable or expression determine where the program will branch to.

112


Program 4-32// The switch statement in this program tells the user

// something he or she already knows: what they just entered!


void main(void)

{

char choice;

cout << "Enter A, B, or C: ";

cin >> choice;


113


Program continues

switch (choice)

{

case 'A': cout << "You entered A.\n";

break;

case 'B': cout << "You entered B.\n";

break;

case 'C': cout << "You entered C.\n";

break;

default: cout << "You did not enter A, B, or C!\n";

}

}

114



Enter A, B, or C: B [Enter]

You entered B.


Enter a A, B, or C: F [Enter]

You did not enter A, B, or C!

115


Program 4-33// The switch statement in this program tells the user

// something he or she already knows: what they just

// entered!


void main(void)

{

char choice;

cout << "Enter A, B, or C: ";

cin >> choice;


116



switch (choice)

{

case 'A': cout << "You entered A.\n";

case 'B': cout << "You entered B.\n";

case 'C': cout << "You entered C.\n";

default: cout << "You did not enter A, B, or C!\n";

}

}

117



Enter a A, B, or C: A [Enter]

You entered A.

You entered B.

You entered C.



Enter a A, B, or C: C [Enter]

You entered C.


118


Program 4-34// This program is carefully constructed to use the

// "fallthrough" feature of the switch statement.


void main(void)

{

int modelNum;

cout << "Our TVs come in three models:\n";

cout << "The 100, 200, and 300. Which do you want? ";

cin >> modelNum;

cout << "That model has the following features:\n";Program continues on next slide…

119


Program continues

switch (modelNum)

{

case 300: cout << "\tPicture-in-a-picture.\n";

case 200: cout << "\tStereo sound.\n";

case 100: cout << "\tRemote control.\n";

break;

default: cout << "You can only choose the 100,";

cout << "200, or 300.\n";

}

}

120



Our TVs come in three models:The 100, 200, and 300. Which do you want? 100 [Enter]That model has the following features:

Remote control.


Our TVs come in three models:The 100, 200, and 300. Which do you want? 200 [Enter]That model has the following features:

Stereo sound.Remote control.

121


Program 4-35// The switch statement in this program uses the "fallthrough"

// feature to catch both upper and lowercase letters entered

// by the user.


void main(void)

{

char feedGrade;

cout << "Our dog food is available in three grades:\n";

cout << "A, B, and C. Which do you want pricing for? ";

cin >> feedGrade;


122



switch(feedGrade){

case 'a':case 'A': cout << "30 cents per pound.\n"; break;case 'b':case 'B': cout << "20 cents per pound.\n"; break;case 'c':case 'C': cout << "15 cents per pound.\n"; break;default: cout << "That is an invalid choice.\

n";}

}

Documents

Starting Out with C++, 3 rd Edition 1 Chapter 4. Making Decisions