Long Distance Call. Long Distance Call 9/28/2015

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1 VISUAL BASIC PROGRAMMING PROJECT Long Distance Call Long Distance Call DESCRIPTION: Write a program that computes the cost of a long-distance call. The cost of the call is determined according to the following rate schedule: a. Any call started between 8:00 am and 6:00 pm, Monday through Friday, is billed at a rate of $0.40 per minute. b. Any call starting before 8:00 am or after 6:00 pm, Monday through Friday, is charged at a rate of $0.25 per minute. c. Any call started on a Saturday or Sunday is charged at a rate of $0.15 per minute. The input will consist of the day of the week, the time the call started, and the length of the call in minutes. The output will be the cost of the call. The time is to be input in 24-hour notation, so the time 1:30 pm is input as 13:30 The number of minutes will be input as a value of type Integer. (You can assume that the user rounds the input to a whole number of minutes.) 1

2 Analyze the Problem O Break it up into smaller pieces O Identify the Inputs and Outputs O Determine the Processing and any additional variables O See if anything special needs to be done with the inputs or outputs DESCRIPTION: Identify the Inputs and Outputs Write a program that computes the cost of a long-distance call. The cost of the call is determined according to the following rate schedule: a. Any call started between 8:00 am and 6:00 pm, Monday through Friday, is billed at a rate of $0.40 per minute. b. Any call starting before 8:00 am or after 6:00 pm, Monday through Friday, is charged at a rate of $0.25 per minute. c. Any call started on a Saturday or Sunday is charged at a rate of $0.15 per minute. The input will consist of the day of the week, the time the call started, and the length of the call in minutes. The output will be the cost of the call. INPUT PROCESSING OUTPUT DayOfWeek TimeStarted LengthOfCall CostOfCall 2

3 Determine the Processing DESCRIPTION: Write a program that computes the cost of a long-distance call. The cost of the call is determined according to the following rate schedule: a. Any call started between 8:00 am and 6:00 pm, Monday through Friday, is billed at a rate of $0.40 per minute. b. Any call starting before 8:00 am or after 6:00 pm, Monday through Friday, is charged at a rate of $0.25 per minute. c. Any call started on a Saturday or Sunday is charged at a rate of $0.15 per minute. INPUT PROCESSING OUTPUT DayOfWeek TimeStarted LengthOfCall If DayOfWeek = Mo through Fr If time >= 800 and time <= 1800 Then rate = 0.40 else if time < 800 or time > 1800 rate = 0.25 Else If DayOfWeek = Sa or DayOfWeek = Su rate = 0.15 CostOfCall = rate * LengthOfCall CostOfCall Get The Inputs The inputs for this program are just a little complicated: O DayOfWeek is a collection of RadioButtons. Only one RadioButtion can be active at a time. O TimeStarted is input like 7:35 an integer for the hour, a colon character and an integer for minutes O LengthOfCall in minutes. This is a simple one. You input the value using an Integer. 3

4 RadioButtons 9/28/2015 Sample Program Design Label used for the program's output. Set the AutoSize property to False Name Each Control (You can use different names, but the names you choose must be consistent the entire program) radsu radmo radtu radwe radth radfr radsa txtcallstart txtlengthofcall btncompute lblcostofcall 4

5 Create the Button's Event Handler Display the Design view. Double-click the 'Compute' button to create the code for the Compute button Event Handler. Define Constants for Billing Rates Use constants to define the billing rates. Place the constants at the top of the program. Since the billing rates have digits past the decimal, use either the Double or Decimal data type. 5

6 Define Variables Used in the Program Since the hour and minute are separated by a colon character in the user's input (example 17:35 is entered for 5:35pm), the variables for hour and minute will be defined a little later. Separate the Hour and Minute The start time is entered by the user into the txtcallstart TextBox in 24-hour format. For example, 5:35pm is entered as 17:35. The TextBox contains a collection of characters. It does not contain numeric values. The program needs to find the colon character and set the hours to the characters before the colon, and the minutes to the characters after the colon. These two character String values can then be converted into Integer values for use by the program. 6

7 Define Additional Variables Define some additional variables that will be used for parsing (separating parts of a string) the Start Time string. Place these variables after the variables that have already been defined. Find the Position of the Colon ":" The String library in Visual Basic has several Methods (functions or subroutines) that can be used to manipulate strings. The InStr method is used to find the position of one string within another string. For Example, if the contents of txtcallstart.text is "17:43" Dim ColonPosition As Integer ColonPosition = InStr(txtCallStart.Text, ":") The variable ColonPosition would be set to a 3 after InStr executes. 17:43 7

8 The Mid String Method The Mid String method is used to extract one string from the middle of another string. There are two ways of calling the Mid string method: 1) With two arguments The original string is the first argument and the starting position is the second argument. Mid returns all of the characters from the start position to the end of the string. 2) With three arguments The original string is the first argument the starting position is the second argument, and the number of characters to be returned is the third argument. The Mid String Method The Mid String method is used to extract one string from the middle of another string. There are two ways of calling the Mid string method: 1) With two arguments The original string is the first argument and the starting position is the second argument. Mid returns all characters from the start position to the end of the string. 2) With three arguments The original string is the first argument the starting position is the second argument, and the number of characters to be returned is the third argument. NewString = Mid(OriginalString, StartPos, CharCount) Optional 8

9 Get the Hour value The InStr method finds the position of the colon ":" and then Mid is used to get all of the characters up to but not including the ":" For Example, if the contents of txtcallstart.text is "17:43" Dim ColonPosition As Integer Dim HourString As String Dim Hour As Integer ColonPosition = InStr(txtCallStart.Text, ":") HourString = Mid(txtCallStart.Text, 1, ColonPosition - 1) Hour = CInt(HourString) Use -1 for up to but not Start Position including the colon 17:43 Get the Minute Value The Mid is used to get all of the characters after the colon ":" until the end of the string. For Example, if the contents of txtcallstart.text is "17:43" Dim ColonPosition As Integer Dim HourString As String Dim Hour As Integer Dim MinuteString As String Dim Minute As Integer ColonPosition = InStr(txtCallStart.Text, ":") HourString = Mid(txtCallStart.Text, 1, ColonPosition - 1) Hour = CInt(HourString) MinuteString = Mid(txtCallStart.Text, ColonPosition + 1) Minute = Cint(MinuteString) Use +1 to start after the colon. With only 2 parameters, Mid returns the rest of the string. 17:43 9

10 Define Out of Range Exception The InStr, Mid and Cint methods have built-in detection of when they are not able to process their input data. In these cases, they will throw an exception within a Try block that can detected by the Catch block. An out of range value, such as the 57 th hour in a day (57:32) will not be caught because the value 57 is a legal integer even though it is out of range for the number of hours in a day. The program can use an If statement to detect out of range values and then use a Throw statement to exit out of the Try block and into the Catch block. The Exception must first be defined. Dim IllegalTime As Exception = New Exception("Illegal Input Value") If Hour < 0 Or Hour > 23 Then Throw IllegalTime End If The Program So Far (Includes an Exception for out of range Hour or Minute) 10

11 Input the Length Of Call Determine the Billing Rate These are fairly straight forward. Make sure that you use the names of the RadioButtons the way they were defined when the form was being designed. Compute and Display the Bill These are fairly straight forward. Make sure that you use the names of the RadioButtons the way they were defined when the form was being designed. 11

12 The Entire Program 1/2 The Entire Program 2/2 12

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