1. Chapter 3 Control Statements
DDC 2133 Programming II

2. Objectives
To declare bool type and write Boolean expressions using comparison operators .
To implement selection control using simple if statements.
To combine conditions using logical operators (&&, ||, and !).
To implement selection control using if ... else statements.
To implement selection control using nested if statements.
DDC 2133 Programming II

3. Objectives (cont.)
To implement selection control using switch statements.
To write expressions using the conditional operator.
To display formatted output using the stream manipulators.
To know the rules governing operand evaluation order, operator precedence, and operator associativity.
DDC 2133 Programming II

4. The bool Type and Operators
Values: true, false
C++ provides six relational operators (also known as comparison operators) to compare two values.
bool done; bool isGreater;
done = false; isGreater = 5 < 3; //isGreater == false
DDC 2133 Programming II

5. Comparison Operators
DDC 2133 Programming II

6. Simple if Statements if (radius >= 0) {
area = radius * radius * PI;
cout << "The area for the circle of " <<
" radius " << radius << " is " << area; }
if (booleanExpression) { statement(s); }
DDC 2133 Programming II

7. Compound Condition
DDC 2133 Programming II

8. Examples
Build a program that checks whether a number is even or odd. The program prompts the user to enter an integer and displays “number is even” if it is even and “number is odd” if it is odd.
DDC 2133 Programming II

9. #include <iostream> using namespace std; int main() {
int number;
cout << "Enter an integer: ";
cin >> number;
if (number % 2 == 0)
cout << number << " is even.";
if (number % 2 != 0)
cout << number << " is odd.";
return 0; }
DDC 2133 Programming II

10. Caution
Adding a semicolon at the end of an if clause is a common mistake.
This mistake is hard to find, because it is not a compilation error or a runtime error, it is a logic error.
DDC 2133 Programming II

11. Boolean Operators Operator Name ! not && and || or
DDC 2133 Programming II

12. Truth Table for Operator !
DDC 2133 Programming II

13. Truth Table for Operator &&
DDC 2133 Programming II

14. Truth Table for Operator ||
DDC 2133 Programming II

15. Examples
Build a program that checks whether a number is divisible by 2 and 3, whether a number is divisible by 2 or 3, and whether a number is divisible by 2 or 3 but not both:
DDC 2133 Programming II

16. #include <iostream> using namespace std; int main() {
int number;
cout << "Enter an integer: ";
cin >> number;
if (number % 2 == 0 && number % 3 == 0)
cout << number << " is divisible by 2 and 3." << endl;
if (number % 2 == 0 || number % 3 == 0)
cout << number << " is divisible by 2 or 3." << endl;
if ((number % 2 == 0 || number % 3 == 0) &&
!(number % 2 == 0 && number % 3 == 0))
cout << number << " divisible by 2 or 3, but not both." << endl;
return(0); }
DDC 2133 Programming II

17. The if...else Statement
if (booleanExpression) { statement(s)-for-the-true-case; } else { statement(s)-for-the-false-case;
DDC 2133 Programming II

18. Examples
Build a program that lets the user enter a year and checks whether it is a leap year.
A year is a leap year if it is divisible by 4 but not by 100 or if it is divisible by 400. So you can use the following Boolean expression to check whether a year is a leap year:
(year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)
DDC 2133 Programming II

19. #include <iostream> using namespace std; int main() {
cout << "Enter a year: ";
int year;
cin >> year;
// Check if the year is a leap year
bool isLeapYear =
(year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
// Display the result in a message dialog box
if (isLeapYear)
cout << year << " is a leap year.";
else
cout << year << " is a not leap year."<<endl;
return 0; }
DDC 2133 Programming II

20. Multiple Alternative if Statements
DDC 2133 Programming II

21. Trace if-else statement
animation
Trace if-else statement
Suppose score is 70.0
The condition is false
if (score >= 90.0)
grade = 'A';
else if (score >= 80.0)
grade = 'B';
else if (score >= 70.0)
grade = 'C';
else if (score >= 60.0)
grade = 'D';
else
grade = 'F';
DDC 2133 Programming II

22. Trace if-else statement
animation
Trace if-else statement
Suppose score is 70.0
The condition is false
if (score >= 90.0)
grade = 'A';
else if (score >= 80.0)
grade = 'B';
else if (score >= 70.0)
grade = 'C';
else if (score >= 60.0)
grade = 'D';
else
grade = 'F';
DDC 2133 Programming II

23. Trace if-else statement
animation
Trace if-else statement
Suppose score is 70.0
The condition is true
if (score >= 90.0)
grade = 'A';
else if (score >= 80.0)
grade = 'B';
else if (score >= 70.0)
grade = 'C';
else if (score >= 60.0)
grade = 'D';
else
grade = 'F';
DDC 2133 Programming II

24. Trace if-else statement
animation
Trace if-else statement
Suppose score is 70.0
grade is C
if (score >= 90.0)
grade = 'A';
else if (score >= 80.0)
grade = 'B';
else if (score >= 70.0)
grade = 'C';
else if (score >= 60.0)
grade = 'D';
else
grade = 'F';
DDC 2133 Programming II

25. Trace if-else statement
animation
Trace if-else statement
Suppose score is 70.0
Exit the if statement
if (score >= 90.0)
grade = 'A';
else if (score >= 80.0)
grade = 'B';
else if (score >= 70.0)
grade = 'C';
else if (score >= 60.0)
grade = 'D';
else
grade = 'F';
DDC 2133 Programming II

26. Note
The else clause matches the most recent if clause in the same block.
DDC 2133 Programming II

27. Nested if Statements
if (i > k) { if (j > k) cout << "i and j are greater than k"; } else cout << "i is less than or equal to k";
DDC 2133 Programming II

28. Note, cont.
Nothing is printed from the preceding statement. To force the else clause to match the first if clause, you must add a pair of braces:
int i = 1; int j = 2; int k = 3;
if (i > j) {
if (i > k)
cout << "A"; }
else
cout << "B";
This statement prints B.
DDC 2133 Programming II

29. TIP
DDC 2133 Programming II

30. CAUTION
DDC 2133 Programming II

31. Example: Computing Taxes
The US federal personal income tax is calculated based on the filing status and taxable income. There are four filing statuses: single filers, married filing jointly, married filing separately, and head of household. The tax rates for 2002 are shown in Table 3.6.
DDC 2133 Programming II

32. Example: Computing Taxes, cont.
#include <iostream>
using namespace std;
int main() {
// Prompt the user to enter filing status
cout << "Enter the filing status\n"
<< "(0-single filer, 1-married jointly,\n"
<< "2-married separately, 3-head of household): ";
int status;
cin >> status;
// Prompt the user to enter taxable income
cout << "Enter the taxable income: ";
double income;
cin >> income;
// Compute tax
double tax = 0;
DDC 2133 Programming II

33. // Compute tax for single filers if (income <= 6000)
if (status == 0) {
// Compute tax for single filers
if (income <= 6000)
tax = income * 0.10;
else if (income <= 27950)
tax = 6000 * (income ) * 0.15;
else if (income <= 67700)
tax = 6000 * ( ) *
(income ) * 0.27;
else if (income <= )
( ) * (income ) * 0.30;
else if (income <= )
( ) * ( ) *
(income ) * 0.35;
else
( ) * (income ) * 0.386; }
DDC 2133 Programming II

34. // Compute tax for married file jointly // Left as exercise }
else if (status == 1) {
// Compute tax for married file jointly
// Left as exercise }
else if (status == 2)
// Compute tax for married separately
else if (status == 3)
// Compute tax for head of household
else
cout << "Error: invalid status";
return (0);
// Display the result
cout << "Tax is " << static_cast<int>(tax * 100) / << endl;
DDC 2133 Programming II

35. switch Statements
switch (status) { case 0: compute taxes for single filers; break; case 1: compute taxes for married file jointly; case 2: compute taxes for married file separately; case 3: compute taxes for head of household; default: System.out.println("Errors: invalid status"); System.exit(0); }
DDC 2133 Programming II

36. switch Statement Flow Chart
DDC 2133 Programming II

37. switch Statement Rules
The switch-expression must yield a value of char, byte, short, or int type and must always be enclosed in parentheses.
switch (switch-expression) {
case value1: statement(s)1;
break;
case value2: statement(s)2; …
case valueN: statement(s)N;
default: statement(s)-for-default; }
The value1, ..., and valueN must have the same data type as the value of the switch-expression. The resulting statements in the case statement are executed when the value in the case statement matches the value of the switch-expression. Note that value1, ..., and valueN are constant expressions, meaning that they cannot contain variables in the expression, such as 1 + x.
DDC 2133 Programming II

38. switch Statement Rules
The keyword break is optional, but it should be used at the end of each case in order to terminate the remainder of the switch statement. If the break statement is not present, the next case statement will be executed.
switch (switch-expression) {
case value1: statement(s)1;
break;
case value2: statement(s)2; …
case valueN: statement(s)N;
default: statement(s)-for-default; }
The default case, which is optional, can be used to perform actions when none of the specified cases matches the switch-expression.
The case statements are executed in sequential order, but the order of the cases (including the default case) does not matter. However, it is good programming style to follow the logical sequence of the cases and place the default case at the end.
DDC 2133 Programming II

39. Trace switch statement
animation
Trace switch statement
Suppose ch is 'a':
switch (ch) {
case 'a': cout << ch;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

40. Trace switch statement
animation
Trace switch statement
ch is 'a':
switch (ch) {
case 'a': cout << ch;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

41. Trace switch statement
animation
Trace switch statement
Execute this line
switch (ch) {
case 'a': cout << ch;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

42. Trace switch statement
animation
Trace switch statement
Execute this line
switch (ch) {
case 'a': cout << ch;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

43. Trace switch statement
animation
Trace switch statement
Execute this line
switch (ch) {
case 'a': cout << ch;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

44. Trace switch statement
animation
Trace switch statement
Execute next statement
switch (ch) {
case 'a': cout << ch;
case 'b': cout << ch;
case 'c': cout << ch; }
Next statement;
DDC 2133 Programming II

45. Trace switch statement
animation
Trace switch statement
Suppose ch is 'a':
switch (ch) {
case 'a': cout << ch;
break;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

46. Trace switch statement
animation
Trace switch statement
ch is 'a':
switch (ch) {
case 'a': cout << ch;
break;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

47. Trace switch statement
animation
Trace switch statement
Execute this line
switch (ch) {
case 'a': cout << ch;
break;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

48. Trace switch statement
animation
Trace switch statement
Execute this line
switch (ch) {
case 'a': cout << ch;
break;
case 'b': cout << ch;
case 'c': cout << ch; }
DDC 2133 Programming II

49. Trace switch statement
animation
Trace switch statement
Execute next statement
switch (ch) {
case 'a': cout << ch;
break;
case 'b': cout << ch;
case 'c': cout << ch; }
Next statement;
DDC 2133 Programming II

50. Conditional Operator if (x > 0) y = 1 else y = -1; is equivalent to
y = (x > 0) ? 1 : -1;
(booleanExpression) ? expression1 : expression2
DDC 2133 Programming II

51. cout << ((num % 2 == 0) ? "num is even" : "num is odd");
Conditional Operator
cout << ((num % 2 == 0) ? "num is even" : "num is odd");
DDC 2133 Programming II

52. Conditional Operator, cont.
(booleanExp) ? exp1 : exp2
DDC 2133 Programming II

53. Formatting Output
DDC 2133 Programming II

54. Operator Precedence How to evaluate 3 + 4 * 4 > 5 * (4 + 3) – 1?
DDC 2133 Programming II

55. Operator Precedence var++, var--
+, - (Unary plus and minus), ++var,--var
(type) Casting
! (Not)
*, /, % (Multiplication, division, and remainder)
+, - (Binary addition and subtraction)
<, <=, >, >= (Comparison)
==, !=; (Equality)
&& (Conditional AND) Short-circuit AND
|| (Conditional OR) Short-circuit OR
=, +=, -=, *=, /=, %= (Assignment operator)
DDC 2133 Programming II

56. Enumerated Types
enum Day {MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY};
Once a type is defined, you can declare a variable of that type:
Day day;
The variable day can hold one of the values defined in the enumerated type. For example, the following statement assigns enumerated value MONDAY to variable day:
day = MONDAY;
DDC 2133 Programming II

57. Enumerated Types
As with any other type, you can declare and initialize a variable in one statement:
Day day = MONDAY;
Furthermore, C++ allows you to declare an enumerated type and variable in one statement. For example,
enum Day {MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY} day = MONDAY;
DDC 2133 Programming II

58. #include <iostream>
using namespace std;
int main() {
enum Day {MONDAY = 1, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY} day;
cout << "Enter a day (1 for Monday, 2 for Tuesday, etc): ";
int dayNumber;
cin >> dayNumber;
switch (dayNumber) {
case MONDAY:
cout << "Play soccer" << endl;
break;
case TUESDAY:
cout << "Piano lesson" << endl;
case WEDNESDAY:
cout << "Math team" << endl;
default:
cout << "Go home" << endl; }
return 0;
DDC 2133 Programming II