CSI 101 Spring 2009 Review and Recap of Visual Basic Wednesday, April 29 th

List of Concepts Variables and Data types Conditional processing Looping Specialized functions –Type Conversion –String Manipulation –File Processing –Formatting –Date processing

List of Concepts, cont Subroutines and functions Classes and objects Events and event procedures Using properties

What you’re good at Variables and data types IF statements Setting up functions (FUNCTION statement) File processing

What we’ll skip Classes and objects –Covered pretty well in previous lecture Type conversion –List in inside front cover of text –Encountered in class examples and homework Formatting –For aesthetic output, not functionally important

Quick recap - Conditional SELECT statement –Alternative to IF –Allows large number of alternatives –Condition tested is a VALUE, not a Yes or No response

SELECT example Check if a string starts with a letter or digit

SELECT example Check if a string starts with a letter or digit SELECT CASE Left(testString,1) CASE “A” to “Z” MsgBox(“Starts with letter”) CASE “a” to “z” MsgBox(“Starts with letter”) CASE “0” to “9” MsgBox(“Starts with digit”) End Select

Looping Recap DO or FOR DO has two conditions –Until or While –Can be placed at beginning (with DO) or end (with Loop) Do ends with Loop For ends with Next

For example with array Calculate the average of the values in an array Need a running sum Use Length method on arrays to get count

For example with array - code Dim index As Byte, sum as Integer = 0 For index = 1 to array.length sum += array(index) Next index Dim average As Decimal = sum/array.length

For example with strings Count number of lowercase letter ‘s’ in a particular string Need to look at EACH character in the string at a time Need running count Use a variable much like an array index to mark where we are in the string

For example with strings - code Dim count As Byte = 0 Dim index As Byte For index = 1 to Len(testString) If Mid(testString,index,1) = “s” then count += 1 End if Next index

String function Recap Most common ones: –Len(string) – returns number of characters in string –Mid(string,start,len) – returns substring starting at start position and for length of len –Left(string,len) – returns substring which is first len characters of string –Trim(string) – remove leading and trailing blanks

Properties and Dates Let’s finish last ones with an interesting example: –We’ll read employee records from a file –Assume we already have an employee structure –If date of last raise is greater than 18 months, increase salary by 4% –Place employee name and new salary into text boxes on the form –This is contained in the event procedure for the NEXT button

Needs Open file OUTSIDE of event procedure –Procedure looks for NEXT employee who requires a raise –Reopening file would start us back at the beginning Remember to Refresh

Code Example Code outside of event procedure: –Definition of Employee structure Key fields: –Name –LastRaise –Salary –Opening file: FileOpen(1, “Employees”)

Code Example, cont Within procedure: Sub btnNext_Click() Dim inEmp As Employee Dim found As Boolean = False Do until found = True Or EOF(1) FileGet(1,inEmp) If DateDiff(“m”,inEmp.LastRaise, Now()) >= 18 then inEmp.Salary *=.04

Code example, cont. found = True txtName.Text = inEmp.Name txtSalary.Text = CStr(inEmp.Salary) End if Loop ‘Check if not found If found = False then txtName.Text = “DONE” Refresh End Sub