1. If/Else Statements

2. Blocks
A Block is a set of 0 or more statements between braces { } It allows several statements to syntactically operate as one statement.

3. Blocks
Blocks usually mark the begin and end of some control statement, such as the main() program void main() { // 0 or more statements here }

4. Blocks Style 1: recommended
The braces should be on their own line, lined up with each other and the control statement, with all statements between indented:
void main() {
// 0 or more statements here, indented }

5. Blocks
Style 2: common (space saver) Another common style is to put the { at the end of the control statement, the } on a line below, lined up with the control statement, and all lines between indented. void main() { // 0 or more statements here }

6. Conditional Expressions
A Conditional Expression is an expression that evaluates to true or false. Relational Operators are used to create conditional expressions. Logical Operators may also be used.

7. Relational Operators
Relational Operators compare two values of compatible types and result in the value true or false.
C++ operator
Meaning
<
Less Than
<=
Less Than or Equal To
>
Greater Than
>=
Greater Than or Equal To ==
Equal To !=
Not Equal To

8. Relational Operators
= vs. == x = 3 is a command: Change the value of x to 3 x == 3 is a question: Is x equal to 3? (yes or no)

9. Relational Operators
Examples: 3 == 3.0 true 4 < 4 false string x=”Apple”; x == ”apple” false (case sensitive)

10. Logical Operators
operate on one or two Conditional Expressions and result in true or false.
C++ Operator
Meaning and Syntax
&&
AND: Syntax: CondEx && CondEx ||
OR: Syntax: CondEx || CondEx !
NOT: Syntax: !CondEx

11. Logical Operators Semantics: The Truth Table A B A && B A || B ! A
true
false

12. Logical Operators
Examples: (4 > 5) || (3 != 3) false (4 > 5) || (3 == 3) true (4 > 5) && (3 == 3) false (4 < 5) && (3 == 3) true !(4 != 5) false

13. if/else statements
if/else statements are used to determine whether or not certain actions are carried out. They work the same as in Matlab, Python and other languages; the syntax is slightly different.

14. if/else statements
Syntax: if (conditionalExpression) oneStatement_T else oneStatement_F The else oneStatement_F is optional. Note the parentheses are ALWAYS required.

15. if/else statements
Syntax: oneStatement can be either: - Exactly one statement with a semicolon Or - A Block (no semicolon after the } )

16. if/else statements
Semantics: When the conditionalExpression is true - execute oneStatement_T - skip oneStatement_F When the conditionalExpression is false - skip oneStatement_T - execute oneStatement_F (when it exists)

17. if/else statements Style: one statement if (conditionalExpression)
oneStatement_T; //indent
else //line up with if
oneStatement_F; //indent

18. if/else statements Style: blocks #1 if (conditionalExpression)
{ //line up with if
statements //indent
} //line up with {
else
oneStatement_F;

19. if/else statements Style: blocks #2 if (conditionalExpression) {
statements //indent
} //line up with if
else
oneStatement_F;

20. if/else statements Style: blocks #2 if (conditionalExpression) {
statements //indent
} //line up with if
else
oneStatement_F;

21. if/else statements Examples: int a = 3;
if ((a >= 2) || (a < 0)) Prints:
cout << ”Apple\n”; Apple
else Banana
cout << ”Orange\n”;
cout << ”Banana\n”; // STYLE doesn’t matter!

22. if/else statements Examples: int a = 3;
if ((a >= 2) || (a < 0)) Prints:
cout << ”Apple\n”; Apple
else {
cout << ”Orange\n”;
cout << ”Banana\n”; }

23. if/else statements Examples: int a = 3;
if ((a >= 2) && (a < 0)) { Prints:
cout << ”Apple\n”; Banana
cout << ”Orange\n”; }
cout << ”Banana\n”;

24. if/else statements Examples: Nested if/else int a = 3, b = 2;
if (a < 0) Prints:
if (b > 3) Banana
cout << ”Apple\n”;
else // proper style
cout << ”Orange\n”;
cout << ”Banana\n”;

25. if/else statements Examples: Nested if/else int a = 3, b = 2;
if (a < 0) Prints:
if (b > 3) Banana
cout << ”Apple\n”;
else // improper style, but
cout << ”Orange\n”; // no effect on semantics
cout << ”Banana\n”;

26. if/else statements Examples: Nested if/else int a = 3, b = 2;
if (a < 0) { Prints:
if (b > 3) Orange
cout << ”Apple\n”; Banana }
else
cout << ”Orange\n”;
cout << ”Banana\n”;

27. Multiway Decisions
Instead of just “this or that”, sometimes one of several (3 or more) paths needs to be chosen.
The following slide has an example of setting a letter grade based on a percentage (no D’s in this course!)

28. Multiway Decisions
if (perc >= 90) // Multiway Style: grade = ’A’; // just a different else if (perc >=80) // style grade = ’B’; else if (perc >=70) grade = ’C’; else //default decision grade = ’F’;

29. Multiway Decisions
if (perc >= 90) // ”Standard” Style grade = ’A’; // same Semantics else if (perc >=80) grade = ’B’; if (perc >=70) grade = ’C’; else //default decision grade = ’F’;

30. switch statement
Used to make a multi-way decision when 1. The decision is based on ONE variable 2. The variable is not string

31. switch statement
Syntax: switch (variable) { case literal1: statement(s) break; // optional case literal2: default: // optional statement(s) // optional }

32. switch statement
Semantics: Top to bottom, checks if variable == literal If true: begins executing statement(s) does NOT stop at the next case If false: tries the next case break; means skip to end }

33. switch statement
Semantics: default: Execute the following statement(s) if the variable did not match ANY literal

34. switch statement
Style: Varies greatly depending on the problem being solved. As always, choose a style to make the code clear. It should allow for “quick spotting” of case literals.

35. switch statement
Example: typical, compact style char letterGrade = ’C’; string s = ”?”; switch (letterGrade) { case ’A’: s = ”Excellent”; break; case ’B’: s = ”Good”; break; case ’C’: s = ”Average”; break; default: s = ”Invalid”; }

36. switch statement
Example: multiple values per “case” (2 styles) char letterGrade = ’C’; string s=”?”; switch (letterGrade) { case ’A’: // long style case ’a’: s = ”Excellent”; break; case ’B’: case ’b’: s = ”Good”; break; }

37. switch statement
Example: without breaks char letterGrade = ’B’; switch (letterGrade) { Prints: case ’A’: cout << ”Excellent\n”; Good case ’B’: cout << ”Good\n”; Average case ’C’: cout << ”Average\n”; Invalid default: cout << ”Invalid\n”; }

38. Vocabulary Term Definition Block
Set of 0 or more statements between braces. Syntactically acts as one statement
Conditional Expression
Expression that evaluates to TRUE or FALSE
Relational Operator
Operators that compare two values and evaluate to TRUE or FALSE. Ex: < <= > >= == !=
Logical Operator
Operators that operate on one or two conditional expressions and evaluate to TRUE or FALSE. Ex: && || !
Nested
When one statement is inside the control of another statement of the same type. Ex: if/else inside an if/else.