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CSI 101 Elements of Computing Spring 2009

Lecture #13 Programming in Visual Basic March 25 th – April 4 th , 2009. CSI 101 Elements of Computing Spring 2009. Development Steps. Determine algorithm Know what you're doing before you start Define data What do I get from the user? What do I give to the user? Decide needed functions

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CSI 101 Elements of Computing Spring 2009

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  1. Lecture #13 Programming in Visual Basic March 25th – April 4th, 2009 CSI 101Elements of ComputingSpring 2009

  2. Development Steps • Determine algorithm • Know what you're doing before you start • Define data • What do I get from the user? • What do I give to the user? • Decide needed functions • What is already available in the language? • What do I need to create? • Design Forms • What should the user see? • Don't put too much on one Form • Make it easy to read 2

  3. Defining Data • List input and output • Determine best data type • For instance, a Name would be a String • Look for opportunities to create composite types • These are the user-defined types you saw earlier, like Ualb_Student or Employee • Why? Easier to catalog and associate • Fewer “loose” variables running around • Figure out source of information • Files, databases, or user input 3

  4. Library Functions • These are functions that come with the compiler • Supposed to make life easier for developers, as they don't have to “reinvent the wheel” • Main categories: • Mathematical • Type conversion • String manipulation • File manipulation (which we've already seen) • Formating • Date manipulation • There are others, but we won't discuss them in this course 4

  5. Type conversion functions • Probably most important, since all data in text boxes on Form are String • Need to convert to appropriate variable to perform calculations and arithmetic operations • All have form Ctype, where type is the data type desired • CByte, CInt, CLng – convert to Byte, Integer, Long • CDec, CSng, CDbl – convert to Decimal, Single, Double • CBool – converts 0, 1, “True”, “False”, “Yes”, “No” • CDate – converts from valid date format string 5

  6. Conversion Examples • CDate(“01/01/09”) • CDate(“September 11, 2001”) • CBool(1) • CBool(“True”) • CBool(“no”) • CInt(Text1.Text) 6

  7. Mathematical Functions • All trig functions • Log() and exp() • These we might use: • Abs() - returns absolute value • Sqrt() - returns Decimal with square root 7

  8. String Manipulation Functions • Len(String) : returns number of characters in string • Left(String, Int) : returns substring of first Int characters of String • Right(String, Int) : returns substring of last Int characters of String • LCase(String) : returns String in all lowercase • UCase(String) : returns String in all upper case • Mid(String,Pos,Len) : returns substring starting at Pos with Len characters 9

  9. String Manipulation Functions, cont • Mid(String, Pos) : returns substring starting at Pos containing the rest of String • Example: Mid(“ABCDEFG”, 3) returns “CDEFG” • StrComp(String1, String2) • Returns 0 if both strings are the same • Returns 1 if String2 would be alphabetically sorted before String1 • Returns -1 if String1 would be alphabetically sorted before String2 • LTrim(String) : returns String without leading blanks 10

  10. Last String Manipulation Functions • RTrim(String) : returns String without trailing blanks • Trim(String) : returns String without extra blanks at either end • StrReverse(String) : returns String in reverse order • InStr(String1, String2) : returns integer start position of String2 in String1 • Returns 0 if not there • InStr(“ABCDEF”,”B”) returns 2 11

  11. Format function • Format(Value, form) : returns Value formatted in the specified form • Form can be a string or a predefined format • String ex: • Format(454, “#,##0.00”) • Format(ThisDate, “mm/dd/yyyy”) • Predefined ex: • Format(ThisDate, “Long Date”) • Format(454, “Currency”) • Note value can be a String, Date, or numerical value or variable • Form is always a String 12

  12. Numerical Predefined Formats • “General” or “G” : displays without thousand separator • “Currency” or “C” : displays dollar sign, separator, and two decimal places • “Fixed” or “F” : displays at least one digit to the left of decimal and two digits after decimal • “Standard” or “S” : displays thousand separator and two decimal digits • “Percent” : Multiplies number by 100 and displays with percent sign immediately following • “P” : Multiplies number by 100 and displays with percent sign behind number, with a space in between • “Scientific” : Displays in scientific notation with two decimal digits • “E” : Displays in scientific notation with up to six decimal digits 13

  13. Special Numerical Formats • “D” : display numerical value as a string with two decimal digits • “X” : display numerical value as a hexadecimal value • Displays in Base 16 with an X following • In Base 16, 10-15 are displayed as A-F • “True/False” : displays False if value = 0, otherwise True • “Yes/No” : displays No if value = 0, otherwise Yes • “On/Off” : displays Off if value = 0, otherwise On 14

  14. Numerical Format symbols • “0” : display that digit location, even if value is 0 • Format(45,”000”) displays 045 • “#” : displays digit if there, nothing if not • Format(45, “##0”) displays 45 • “.” : decimal placeholder. What follows is number of decimal digits to display • Format(45,”0.00”) displays 45.00 • “,” : thousand separator. If value > 1000, puts comma after thousand digit • “%” : multiplies value by 100 and displays percent sign afterwards 15

  15. Predefined Date/Time formats • “General Date” or “G” : Displays in standard m(m)/d(d)/yyyy format with time following • 10/29/2008 6:50:00 PM • “Long Date” or “D” : displays whole date • Wednesday, October 29, 2008 • “Short Date” or “d” : displays standard date • 10/29/2008 • “M” : display just month and day • October 29 • “Y” : display just month and year • October, 2008 16

  16. Date/Time Format symbols • “d” : displays day without leading zero • “dd” : displays two digits for day • “ddd” : displays day as abbreviated text • Ex: “Wed” • “dddd” : displays full name for day • Month has same format, but with M • Format(Today,”MMM dd”) displays Oct 29 • Format(Today, “MM/dd”) displays 10/29 • Year has same format, but with y • Format(Today,”M/d/yy”) displays 10/29/08 17

  17. Special Format functions • FormatCurrency(value) : returns string with value in currency format • FormatPercent(value) : returns string with value in percent format • FormatDateTime(value, DateFormat) : returns string with value in specified date format: • DateFormat.GeneralDate • DateFormat.LongDate • DateFormat.ShortDate 18

  18. Date Manipulation Functions • Now() : returns current day • Today = Now() • Month(date) : returns integer value for month • Month(Today) returns 10 • MonthName(date,abbr) : returns string name of month • Abbr is a Boolean which says whether to return abbreviated name • MonthName(Today,True) returns Oct • Day(date) : returns integer value of day • Year(date) : returns integer value of year 19

  19. More Date Manipulation Functions • Weekday(date) : returns integer value of day of week (Sunday is 1) • Weekday(Today) returns 4 • WeekdayName(date,abbr) : returns string name of day of week • Abbr is Boolean – should I abbreviate? • WeekdayName(Today) returns Wed 20

  20. Date Arithmetic Functions • DateAdd(interval, amount, date) : Adds amount of interval to date and returns new date • Intervals: • “d” for day • “w” for weekday • “m” for month • “q” for quarter (three months) • “yyyy” for year • DateAdd(“m”, 1, Today) returns Nov 29, 2008 • DateDiff(interval, date1, date2) : returns integral number of intervals between date1 and date2 • DateDiff(“d”,Yesterday,Today) is 1 • DateDiff(“d”,Today,Yesterday) is -1 21

  21. Time Functions • There are functions dealing with time, but we won’t cover them in this course • See the Visual Basic Reference on www.msdn.com 22

  22. Let’s Practice • The rest of this lecture is a demonstration of creating the Form and code for the following problem statement: • “Obtain a name from the user. Search for that name in file Employee. When found, display the employee’s date of hire, current Manager, and current salary.” 23

  23. Steps • Get requirements • Determine algorithm • Define data • Map Form • Write code • Test

  24. Get requirements • Initial problem statement seems fine • Check source file to determine additional questions

  25. Employee file • Each record has these fields: • First Name • Last Name • Manager’s Name • Office number • Office phone number • Date of hire • Salary

  26. Questions to user • Since Employee name is split, do you want to search on either first name or last name? • Answer: “Yes” • Does the user need to specify the exact name, or will a “fuzzy” search do? • Answer: “fuzzy search”

  27. Okay, let’s get to work… • The rest is done on Notepad, in Visual Studio, or on whiteboard. • Slides showing Notepad and whiteboard work will be added to the end of this lecture after the Practice is complete.

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