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Relational Expressions

Relational Expressions. Decision-making: comparison of two numerical values Relational expression Also known as a condition Evaluates to 1 (true) or 0 (false) Simple type: two operands and relational operator Six relational operators: <, >, <=, >=, = =, !=

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Relational Expressions

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  1. Object-Oriented Program Development Using C++

  2. Relational Expressions • Decision-making: comparison of two numerical values • Relational expression • Also known as a condition • Evaluates to 1 (true) or 0 (false) • Simple type: two operands and relational operator • Six relational operators: <, >, <=, >=, = =, != • Char type coerced to int for comparison • Strings compared at character level Object-Oriented Program Development Using C++

  3. Figure 5-1 Anatomy of a Simple Relational Expression Object-Oriented Program Development Using C++

  4. Table 5-1 Relational Operators for Primitive Data Types Object-Oriented Program Development Using C++

  5. Logical Operators • Complex expressions • Comprised of simple relational expressions • Logical connectors required • AND ( && ), OR ( | | ), NOT (!) • Precedence • AND and OR lower than relational operators • NOT (unary) higher than relational operators • Associativity • AND and OR: left to right • NOT: right to left Object-Oriented Program Development Using C++

  6. Table 5-2 Operator Precedence Object-Oriented Program Development Using C++

  7. Table 5-3 Equivalent Expressions Object-Oriented Program Development Using C++

  8. A Numerical Accuracy Problem • Caveat: equality comparison of floating-point types • Avoid use of equality operator • Computer representation slightly inaccurate • Work around problem • If possible, replace floating-point data with integers • If not, use alternative syntax • abs (operandOne - operandTwo) < EPSILON • EPSILON is very small value such as .0000001 Object-Oriented Program Development Using C++

  9. The if-else Statement • if-else statement: fundamental selection structure • Purpose: alter instruction sequence • Syntax: if (expression) statement1; else statement2; • Expression • Relational expression • May consist of single variable, such as type bool Object-Oriented Program Development Using C++

  10. Figure 5-2 The if-else Flowchart Object-Oriented Program Development Using C++

  11. Compound Statements • Compound statement • Sequence of statements enclosed by braces • Supports construction of complex selection structures • Syntax: if (expression){ //sequence of statements } else{ //sequence of statements } Object-Oriented Program Development Using C++

  12. Block Scope • Code block • Set of compound statements • May be nested • Variable scope • Variable meaningful between closing braces • Name conflict resolved by location • Inner block takes precedence over outer • Compiler seeks declaration moving inside out Object-Oriented Program Development Using C++

  13. One-Way Selection • One-way selection: excludes else portion • Syntax: if (expression) statement; // code block might follow • Non-zero expression triggers statement execution Object-Oriented Program Development Using C++

  14. Figure 5-3 Flowchart for the One-Way if Statement Object-Oriented Program Development Using C++

  15. Problems Associated with the if-else Statement • Semantic problems • Logical form • Correct by reviewing original design • Syntax problems • Misuse of assignment operator (=) in expression • Assigns value to operand • Non-zero assignments always evaluate to true • Use equality operator (= =) for comparisons Object-Oriented Program Development Using C++

  16. Nested if Statements • Selection structures may be nested • if or if-else statements nest in either (or both) parts of larger if-else statement • Nesting may be deeper than one level • Syntax caveat • Use braces to define logical unit • Misused (or missing) braces may cause fatal logical error Object-Oriented Program Development Using C++

  17. Figure 5-4a The if-else Nested Within the if Part Object-Oriented Program Development Using C++

  18. Figure 5-4b The if-else Nested Within the else Part Object-Oriented Program Development Using C++

  19. The if-else chain • if-else chain: useful, readable form of nesting • Syntax: if (expression1) statement1; // may be code block else if (expression2) statement2; // may be code block else statement3; // may be code block • Additional else-if components may be added Object-Oriented Program Development Using C++

  20. The Switch Statement • Switch statement • Variation on chained if-else statement • Control “switches” to case based on condition • Caveat: condition evaluates to an integer • Cases may include complex structures • Break statement follows each case • Default statement is optional Object-Oriented Program Development Using C++

  21. Figure 5-5 The Expression Determines an Entry Point Object-Oriented Program Development Using C++

  22. Program Design and Development: Introduction to UML • Think and plan before coding • Primary concern: classes and objects needed • Uniform Modeling Language (UML) • Supports object-oriented design • Set of rules and diagrams • Focus on four UML diagrams • Class, object, state, and sequence • Analogy to specialized blueprints Object-Oriented Program Development Using C++

  23. Figure 5-7 Basic UML Symbols and Notation Object-Oriented Program Development Using C++

  24. Class and Object Diagrams • Commonality of class and object diagrams • Both employ rectangular containers • Names, attributes, behaviors found in both • Chief differences • Class diagram: describes classes and relationships • Object diagram: describes objects and relationships • Class at higher level of abstraction • One class can generate many particular objects Object-Oriented Program Development Using C++

  25. Figure 5-6 A Class and Object Representation Object-Oriented Program Development Using C++

  26. Figure 5-8 Including Attributes in UML Class and Object Diagrams Object-Oriented Program Development Using C++

  27. Class and Object Diagrams (continued) • Two aspects to class attributes • Data type: may be primitive or class • Visibility: where variable may be seen (or used) • Plus (+) sign indicates public • Minus (-) sign indicates private • No sign for protected status • Operations • Become methods that transform attributes • Follow attribute sign convention for visibility Object-Oriented Program Development Using C++

  28. Figure 5-9 A Class with Attributes Object-Oriented Program Development Using C++

  29. Figure 5-10 Including Operations in Class Diagrams Object-Oriented Program Development Using C++

  30. Relationships • Three basic relationships • Association, aggregation, generalization • Association • Signified by phrases such as “works for”, “has a” • Indicated by straight line connecting classes/ objects • Multiplicity • Numerical relationship between objects/classes • Quantities: 0, 1, many, unlimited Object-Oriented Program Development Using C++

  31. Figure 5-11 An Association Object-Oriented Program Development Using C++

  32. Table 5-4 UML Association Notation Object-Oriented Program Development Using C++

  33. Relationships (continued) • Aggregation • One class/object consists of other classes/objects • Visualize as relation of whole to parts • Symbolized by diamond • Generalization • Relationship between class and its refinement • Ford Taurus is a type of automobile Object-Oriented Program Development Using C++

  34. Figure 5-12 Single-Level Aggregation Object-Oriented Program Development Using C++

  35. Figure 5-13 Another Single-Level Aggregation Object-Oriented Program Development Using C++

  36. Figure 5-14 Multi-Level Aggregation Object-Oriented Program Development Using C++

  37. Figure 5-15 A Generalization Relationship Object-Oriented Program Development Using C++

  38. Application: A Date Class • Stage one: identify and name objects • Stage two • Define attributes • Month, day, and year • Integer data types • Stage three • Create object diagram • Object diagram shows assignment of values Object-Oriented Program Development Using C++

  39. Figure 5-16 Initial Date Class Diagram Object-Oriented Program Development Using C++

  40. Figure 5-17 First Refinement-Date Class Diagram Object-Oriented Program Development Using C++

  41. Figure 5-18 A Date Object Diagram Object-Oriented Program Development Using C++

  42. Application: A Date Class (continued) • Stage four • Identify operations that become methods • Basic operations: constructor, mutator, accessor • Additional operations: queries with comparisons • Stage five • Construct second refinement of class diagram • Name, attributes, operations detailed • Visibility denoted Object-Oriented Program Development Using C++

  43. Table 5-5 Required Operations for the Date Class Object-Oriented Program Development Using C++

  44. Figure 5-19 Second Refinement-Date Class Diagram Object-Oriented Program Development Using C++

  45. Explanation of the Basic Date Class • Default constructor • Initializes month, day, year • cout object echo prints default data • Overloaded constructor • Initializes Date object with parameterized interface • cout object echo prints default data • setDate( ): almost identical to overloaded constructor • showDate( ): accessor manipulates output stream Object-Oriented Program Development Using C++

  46. Using the Basic Date Class • Constructors instantiate two Date objects • Syntax of object declaration • If default constructor used, follow primitive form • If overloaded constructor used, supply arguments • Accessors retrieve data in attributes • Output modified according to current values Object-Oriented Program Development Using C++

  47. Simplifying the Code • Opportunities for optimization exist • Call internal methods when possible • Eliminate redundant code • Do not reinvent your own wheel • Example: call setDate( ) in constructors • Dealing with other redundancies • Target common or repeated actions • Fold action into method Object-Oriented Program Development Using C++

  48. Adding Additional Class Methods • Virtue of OO programming: scalability • Add isLeapYear ( ) • Based on leap year algorithm • Returns a Boolean value • Add dayOfWeek ( ) • Based on Zeller’s algorithm • Returns an integer value • Include appropriate declarations, definition, visibility Object-Oriented Program Development Using C++

  49. A Closer Look at Program Testing • Added complexity increases likelihood of errors • Selection structures introduce new control paths • Ideally, programmer tests each path • Not physically possible • Growth of test paths: 2n • n corresponds to number of if-else statements • Choose critical elements to test • Legal and limiting input values Object-Oriented Program Development Using C++

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