Review for Exam 2. IF Blocks. Nested IF Blocks. School of Business Eastern Illinois University. Represent computers abilities to make decisions

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1 School of Business Eastern Illinois University Review for Exam 2 - IF Blocks - Do s - Select Case Blocks (Week 10, Friday 3/21/2003) Abdou Illia, Spring 2003 IF Blocks 2 Represent computers abilities to make decisions Allow a program to decide on a course of action Based on whether a certain condition is true or false Simplest form (Single- Syntax If Condition Then alternative decision): If Credits < 10 Then Tuition = 100 * Credits Condition is an expression that is evaluated by the computer If Condition is true, are executed;otherwise are skipped Nested IF Blocks 3 Nested IF Blocks (IF Blocks contained inside others): Syntax If condition1 Then [] If condition2 Then If Credits > 10 Then Tuition = 1000 If Credits > 15 Then Message = "Over load" Note: In the nested If Blocks, each If must have its own statement Credits Tuition Message 10 Fill in this table indicating the values of variables Tuition and Message for each value of Credits

2 Conditions 4 Expression involving: Relational operators (<, >, >=,.) Logical operators (And, Or, Not) lettergrade = txtgrade.text If ( lettergrade = "A") Or (lettergrade = "B") Then picoutput.print "Good Work" ElseIf (lettergrade = "C") Then picoutput.print " Average Work" Else picoutput.print "Poor Work" Relational operators 5 Mathematical Notation Visual Basic Notation = = # <> < < > > <= >= Numeric Meaning Equal to Unequal to Less than Greater than Less than or equal to Greater than or equal to Applied to numbers. Also applied to strings Relational operators 6 Computer uses a special coding system to compare character strings String1 is said to be less than String2 if String1 precede String2 alphabetically according to ANSI table (See Appendix A). "Chase" < "Chaz" True : Comparing character strings " Cat" < "Cat" True "Pay" < "Pay " True "Jones" <> "James" True "Hope" < "Hopeful" True

3 Logical operators 7 The three Logical Operators are: Not, And, Or Not: Negates a single expression. : Suppose answer = "Y" Not (answer = "y") is true And: Combines two expressions; each expression must be True for the entire expression to be True. : Suppose answer = "Y" (answer = "Y") And (answer = "y") is False Or: Combines two expressions; either expression (or both expressions) must be True for the entire expression to be True. : Suppose answer = "Y" (answer = "Y") Or (answer = "y") is True VB operators hierarchy 8 First, Arithmetic operations (^, *, /, +, -) are carried out Second, Expressions involving relational operators (>, <, =, ) are evaluated to True or False Third, Logical operators are applied in the order Not, And, Or. In the event of a tie, the leftmost operator is applied. Note: Expressions in parentheses evaluated first 9 Determine whether the following conditions are true or false? 1 <= 1 "car" < "cat" (because alphabetically, "car" precedes "cat") "Dog" < "dog" (because Uppercase precedes lowercase) ("Y" < > "X") And ( < ) Answer: False

4 10 Determine whether the following conditions are true or false? (0 = 14) Or (6 ^ 2-3 <= 4 / 2 + 8) Answer: False Not (6 = 7) And ( 44 > 33) In the next two cases, suppose that n = 4 (2 < n) And (n < 6) (2 < n) Or (n = 6) Answer: true 11 Determine whether the following conditions are true or false? In the next cases, assume a = 2 and b = 3 3 * a = 2 * b (5 a) * b < 7 Answer: False b <= 3 a ^ b = b ^ a Answer: false 12 Determine whether the following conditions are true or false? In the next cases, assume a = 2 and b = 3 a ^ (5 2) > 7 (a < b) Or (b < a) (a * a < b) Or Not (a * a < a) Not (a < b) Or Not (a < (b + a)) Answer: False

5 Determine the output displayed in the picture box when the command button is clicked. 13 Dim a As Single a = 5 If 3 * a 4 < 9 Then picoutput.print "Remember, " picoutput.print "Tomorrow is another day." Answer: Tomorrow is another day. Determine the output displayed in the picture box when the command button is clicked. 14 Dim Gpa As Single Gpa = 3.49 If Gpa >= 3.5 Then picoutput.print "Honors"; picoutput.print "Student" Answer: Student Determine the output displayed in the picture box when the command button is clicked. 15 Dim a As Single a = 5 If (a > 2) And (a = 3 Or a <7) Then picoutput.print "Hi" Answer: Hi

6 Do s (using While) 16 Used to repeat a sequence of statements while a condition is True Syntax 1 Do While Condition Syntax 2 Do While Condition Condition involve: Relational operators (<, >, >=,.) Logical operators (And, Or, Not) Dim Num As Integer ' Display the numbers from 1 to 10 Num = 1 Do While Num <= 10 picnumbers.print Num; Num = Num + 1 Same rules than Condition in IF Blocks (seen before Spring Break) Do s (using Until) 17 Used to repeat a sequence of statements until a condition becomes True Syntax 3 Do Until conditon Dim Num As Integer ' Display the numbers from 1 to 10 Num = 1 Do Until Num > 10 Syntax 4 picnumbers.print Num; Do Num = Num + 1 Until condition Note: To get the same result using While and Until, Conditions should be opposites. For instance, While Num <= 10 is the same as Until Num > 10 Do s 18 Used to display all or selected items from a file Using EOF function Phone.txt "Bert", " " "Ernie", " " "Grover", " " "Oscar", " " Dim Name As String, Phone As String picphones.cls Open "A:\Phone.txt" For Input As #1 Do While Not EOF(1) Input #1, Name, Phone picphones.print Name, Phone Close #1

7 Replace each statement containing Until with an equivalent statement containing a While, and vice versa. Until AccountBalance >= 1200 Answer: While AccountBalance < 1200 Do While Amount = 100 Answer: Do Until Amount < > 100 Do Until Name = "Bob" Answer: Do While Name < > "Bob" Do While (a > 1) And (a < 3) Answer: Do Until (a <= 1) Or (a >= 3) Do Until (Answer < > "Y") Or (n >= 7) Answer: Do While (Answer = "Y") And (n < 7) 19 Identify the errors 20 Dim Num As Integer ' Display the numbers from 1 to 10 Do While Num >= 10 Num = 1 picoutut.print Num; Num = Num + 1 Answer: Program never stops. Statement Num = 1 should appear before Do Dim q As Single q = 1 Do While q > 0 q = 3 * q - 1 picoutput.print q; Answer: Program never stops because q = 2 within the loop all time. Identify the errors 21 Dim Num As Single Open DATA.TXT For Input As #1 Do While (Not EOF (1)) And (Num > 0) Input #1, Num picoutut.print Num; Close #1 Note: Assume that DATA.TXT contains: 7, 6, 0, -1, 2 Answer: statement is missing. Also, loop cannot be entered because the (default) value of Num is 0 Dim Num As Integer ' Display numbers Do While 1 < Num < 5 Num = 1 picoutut.print Num; Num = Num + 1 Answer: Invalid condition. Condition should be (1 < Num) And (Num < 5)

8 Simple program using a Do loop 22 The world population reached 6 billion people in 1999 and was growing at the rate of 1.4 percent each year. Assuming that the population will continue to grow at the same rate, write a program to determine when the population will exceed 10 billion. Private Sub cmdcalculate_click( ) Dim Year As Integer, Population As Single Year = 1999 Population = 6 Do Until Population > 10 Population = Population + (0.014 * Population) Year = Year + 1 picoutput.print "The answer is: "; Year For Next 23 Repeats a group of statements a specified number of times For Next are used when we know exactly how many times a loop should be executed. For counter = start To end Where: counter is a numeric variable used as a loop counter start is the initial value of counter Next [counter] end is the final value of counter Dim i As integer pictable.cls For i = 1 To 5 pictable.print i; i^2 Next i Same example using Do loop Dim i As integer pictable.cls i = 1 Do While i <= 5 pictable.print i; i^2 i = i + 1 Select Case Blocks 24 Very efficient decision-making structures: Simplifies choosing among several actions Avoid using Nested IF and ElseIf statements Actions based on the value of an expression called selector Syntax Select Case Selector Case ValueList1 Action1 Case ValueList2 Action2 : Case Else Action of last resort Age = Val(txtAge.Text) Select Case Age Case 5 Category = "5-year old" Case 13 To 19 Category = "Teenager" Case Is > 65 Category = "Senior" Case Else Category = "Everyone else"

9 Syntax Select Case Selector Case ValueList1 Action1 Select Case Statements Case ValueList2 Action2 : Case Else Action of last resort Selectors can be: Numeric or string variables. : Select Case FirstName Expressions. : Select Case Left(EmployeeName, 1) ValueList items must be separated by commas ValueList can be: A constant An expression An inequality sign preceded by Is and followed by a constant, a variable, or an expression A range expressed in the form a To b. Grade = Val(txtBox.Text) Select Case Grade Case 60 To 89 picoutput.print "Pass" 25 x = 2 : y = 3 Num = Val(txtNumber.Text) Select Case Num Case y x, x picoutput.print "Buckle my shoes" Grade = Val(txtBox.Text) Select Case Grade Case Is >= 90 picoutput.print "A" Problem 1: Assigning letter grades (To be done in class) 26 Write a Click event procedure associated to the command button cmdshow that asks the user to type in an exam score and: Assigns a letter grade based on the scale in the table below. The variable to be assigned the letter grade as value should be named Grade Displays the score typed by the user and the letter grade in picbox. txtscore Score Letter grade A B C D 0-59 F cmdshow picbox Problem 1: Assigning letter grades Private Sub cmdshow_click() Dim Score As Single Score = Val(txtScore.Text) Select Case Score Case 90 To 100 Grade = "A" Case 80 To 89 Grade = "B" Case 70 To 79 Grade = "C" Case 60 To 69 Grade = "D" Case 0 To 59 Grade = "F" picbox.print Score; Grade Score Letter grade A B C D 0-59 F txtscore cmdshow picbox 27

10 Problem 2: IRS 28 IRS informants are paid cash rewards based on the value of the money recovered. Write a Click event procedure associated to the command button cmdreward that asks the user to type in the Amount recovered and: Determine the Reward based on the following rule: 10% for up to $75000 recovered, 15% for a recovered amount greater than but less than $100000; and 18% for more than $ Displays the calculated reward in picreward. txtamount picreward cmdshow Problem 2: IRS picreward cmdshow Private Sub cmdshowreward_click() Dim Amount As Single Amount = Val(txtAmount.Text) Select Case Amount Case Is <= Reward = 0.1 * Amount Case Is <= Reward = 0.15 * Amount Case Is > Reward = 0.18 * Amount picreward.print "The reward is "; Reward txtamount 29 Identify the errors. 30 Dim num As Single num = 2 Select Case num picoutput.print "Two" Answer: Case statement is missing.

11 Identify the errors. 31 Dim num As Single num = 5 Select Case num Case 5, Is <>5 picoutput.print "Five" Case Is > 5 picoutput.print "Greater than 5" Answer: - First Case statement is executed every time, no matter the value of num - Should have an. Suppose the selector of a Select Case statement, 32 word, evaluates to a string value. Determine whether the Case clause is valid. Case Left("abc", 1) Answer: Valid Case word < > "No" Answer: Invalid. Should be Case Is < > "No" Case 0 To 9 Answer: Invalid (because 0 To 9 doesn t refer to a string value) Case "Hello", Is < "goodbye" Answer: Valid Case "un" & "til" Answer: Valid (because "un" & "til" will give until)