Csc153 chapter 04
- 1. Microsoft Visual C# 2010 Fourth Edition Chapter 4 Making Decisions
- 2. Objectives • Understand logic-planning tools and decision making • Learn how to make decisions using the if statement • Learn how to make decisions using the if-else statement • Use compound expressions in if statements Microsoft Visual C# 2010: Fourth Edition 2
- 3. Objectives (cont'd.) • Make decisions using the switch statement • Use the conditional operator • Use the NOT operator • Learn to avoid common errors when making decisions • Learn about decision-making issues in GUI programs Microsoft Visual C# 2010: Fourth Edition 3
- 4. Understanding Logic-Planning Tools and Decision Making • Pseudocode – Tool that helps programmers plan a program’s logic by writing plain English statements • Flowchart – You write the steps in diagram form as a series of shapes connected by arrows • Sequence structure – One step follows another unconditionally – Sometimes, logical steps do not follow in an unconditional sequence Microsoft Visual C# 2010: Fourth Edition 4
- 5. Understanding Logic-Planning Tools and Decision Making (cont'd.) Microsoft Visual C# 2010: Fourth Edition 5
- 6. Understanding Logic-Planning Tools and Decision Making (cont'd.) • Decision structure – Involves choosing between alternative courses of action based on some value within a program – All computer decisions are yes-or-no decisions • When reduced to their most basic form Microsoft Visual C# 2010: Fourth Edition 6
- 7. Understanding Logic-Planning Tools and Decision Making (cont'd.) Microsoft Visual C# 2010: Fourth Edition 7
- 8. Making Decisions Using the if Statement • if statement – Used to make a single-alternative decision • Block – One or more statements contained within a pair of curly braces Microsoft Visual C# 2010: Fourth Edition 8
- 9. Making Decisions Using the if Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 9
- 10. Making Decisions Using the if Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 10
- 11. Making Decisions Using the if Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 11
- 12. Making Decisions Using the if Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 12
- 13. Making Decisions Using the if Statement (cont'd.) • Nested if – One decision structure is contained within another Microsoft Visual C# 2010: Fourth Edition 13
- 14. Making Decisions Using the if Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 14
- 15. Making Decisions Using the if Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 15
- 16. Making Decisions Using the if-else Statement • Dual-alternative decisions – Have two possible outcomes • if-else statement – Used to perform one action when a Boolean expression evaluates as true • And an alternate action when it evaluates as false Microsoft Visual C# 2010: Fourth Edition 16
- 17. Making Decisions Using the if-else Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 17
- 18. Making Decisions Using the if-else Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 18
- 19. Using Compound Expressions in if Statements • You can combine multiple decisions into a single if statement – Using a combination of AND and OR operators Microsoft Visual C# 2010: Fourth Edition 19
- 20. Using the Conditional AND Operator • Conditional AND operator – Determines whether two expressions are both true – Written as two ampersands (&&) – You must include a complete Boolean expression on each side of the operator • Short-circuit evaluation – Expressions in each part of an AND expression are evaluated only as much as necessary • To determine whether the entire expression is true or false Microsoft Visual C# 2010: Fourth Edition 20
- 21. Using the Conditional AND Operator (cont'd.) Microsoft Visual C# 2010: Fourth Edition 21
- 22. Using the Conditional OR Operator • Conditional OR operator – Used when you want some action to occur even if only one of two conditions is true – Written as || Microsoft Visual C# 2010: Fourth Edition 22
- 23. Using the Conditional OR Operator (cont'd.) Microsoft Visual C# 2010: Fourth Edition 23
- 24. Using the Logical AND and OR Operators • Boolean logical AND (&) and Boolean logical inclusive OR (|) operators – Work just like their && and || (conditional AND and OR) counterparts – They do not support short-circuit evaluation – Can lead to a side effect (unintended consequence) • Avoid writing expressions that contain side effects Microsoft Visual C# 2010: Fourth Edition 24
- 25. Combining AND and OR Operators Microsoft Visual C# 2010: Fourth Edition 25
- 26. Making Decisions Using the switch Statement • switch structure – Tests a single variable against a series of exact matches • Keywords – switch, case, break, and default • “No fall through rule” – Not allowing code to reach the end of a case – Not allowed in C# – Use a break statement at the end of each case Microsoft Visual C# 2010: Fourth Edition 26
- 27. Making Decisions Using the switch Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 27
- 28. Making Decisions Using the switch Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 28
- 29. Making Decisions Using the switch Statement (cont'd.) • A switch does not need a default case – Good programming practice to include one • You can use multiple labels to govern a list of statements Microsoft Visual C# 2010: Fourth Edition 29
- 30. Making Decisions Using the switch Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 30
- 31. Using an Enumeration with a switch Statement • Using an enumeration with a switch structure can often be convenient Microsoft Visual C# 2010: Fourth Edition 31
- 32. Using an Enumeration with a switch Statement (cont'd.) Microsoft Visual C# 2010: Fourth Edition 32
- 33. Using the Conditional Operator • Conditional operator – Used as an abbreviated version of the if-else statement – A ternary operator • Syntax testExpression ? trueResult : falseResult; Microsoft Visual C# 2010: Fourth Edition 33
- 34. Using the NOT Operator • NOT operator – Written as an exclamation point (!) – Negates the result of any Boolean expression Microsoft Visual C# 2010: Fourth Edition 34
- 35. Avoiding Common Errors When Making Decisions • Most frequent errors include: – Using the assignment operator instead of the comparison operator – Inserting a semicolon after the Boolean expression in an if statement – Failing to block a set of statements with curly braces – Failing to include a complete Boolean expression on each side of an && or || operator Microsoft Visual C# 2010: Fourth Edition 35
- 36. Performing Accurate and Efficient Range Checks • Range check – A series of if statements that determine whether a value falls within a specified range • Problem Microsoft Visual C# 2010: Fourth Edition 36
- 37. Performing Accurate and Efficient Range Checks (cont'd.) • Solution if(saleAmount >= 1000) commissionRate = 0.08; else if(saleAmount >= 500) commissionRate = 0.06; else commissionRate = 0.05; Microsoft Visual C# 2010: Fourth Edition 37
- 38. Using && and II Appropriately • Problem – Print an error message when an employee’s hourly pay rate is under $5.65 and when an employee’s hourly pay rate is over $60 • Solution if(payRate < 5.65 || payRate > 60) Console.WriteLine (“Error in pay rate”); Microsoft Visual C# 2010: Fourth Edition 38
- 39. Using the ! Operator Correctly • Problem – Make sure that if the sales code is not ‘A’ or ‘B’, the customer gets a 10% discount • Solutions if(salesCode != ‘A’ && salesCode != ‘B’) discount = 0.10; if(!(salesCode == ‘A’ || salesCode == ‘B’)) discount = 0.10; Microsoft Visual C# 2010: Fourth Edition 39
- 40. Decision-Making Issues in GUI Programs • Making a decision within a method in a GUI application is no different from making one in a console application • You can use if, if…else, and switch statements in the same ways Microsoft Visual C# 2010: Fourth Edition 40
- 41. Decision-Making Issues in GUI Programs (cont'd.) Microsoft Visual C# 2010: Fourth Edition 41
- 42. Decision-Making Issues in GUI Programs (cont'd.) Microsoft Visual C# 2010: Fourth Edition 42
- 43. You Do It • Activities to explore – Using if-else Statements – Using AND and OR Logic Microsoft Visual C# 2010: Fourth Edition 43
- 44. Summary • A flowchart is a pictorial tool that helps you understand a program’s logic • You use an if statement to make a single- alternative decision • When you make a dual-alternative decision, you can use an if-else statement • Conditional AND operator determines whether two expressions are both true • Use the conditional OR operator when you want some action to occur when one or both of two conditions are true Microsoft Visual C# 2010: Fourth Edition 44
- 45. Summary (cont'd.) • AND operators take precedence • The switch statement tests a single variable against a series of exact matches • The conditional operator is used as an abbreviated version of the if-else statement • You use the NOT operator to negate the result of any Boolean expression • Common errors when making decisions • Decisions within GUI methods are just like ones in console applications Microsoft Visual C# 2010: Fourth Edition 45