VB Quick Reference
Programming Usable
Interfaces (05-630/05-430)
Spring 2004
[Includes material
from http://www.garybeene.com/vb/tutor.htm]
Declarations
·
Dim - Used to define a variable
as a certain type. DIM is that simplest way to declare a variable.
Dim varName
as VarType
Possible
types include Integer, String, Double (floating point), Boolean
VB
will let you leave off the VarType declaration, or let you use Object
(the equivalent was called Variant in VB6) as the type (can store
any type). Both of these options are bad ideas: then YOU have to
keep track of the type of the variable and make sure you do the right thing. Uuse
types so that VB can help you find your bugs.
In
VB.Net, you can declare the variable and initialize it in one step:
Dim myInt as Integer = 42
VB 6 only
Option
Explicit - Instructs VB to force an explicit declaration of all variables
Make sure you use this, so VB can catch your typos!
Use Tools->Options->Require
Variable Declaration to turn on Option Explicit for all your projects.
· Const - Creates a variable whose value is fixed
Const kgToPound = 2.205
· Call - Transfers control to a Sub or Function (is optional)
Call Procedure 1
Since the use of CALL is optional, you can ignore this.
· Sub - Defines a method which can execute a block of code
Sub methodName (var1 as VarType, var2 as VarType, var3 as VarType)
Be sure to check out HELP for how to handle Sub arguments.
· Function - Declares a procedure which can return a value
Function functionName (var1 as VarType, var2 as VarType) as VarType
This is the most versatile of the Sub/Function procedure types. It can do anything a Sub can do as well as returning a value for use in an expression.
To return a value:
VB 6 functionName = value
VB.Net return value
VB 6 only
·
Array – A
function that returns an array that has been filled with data from a list. It
allows you to put the actual data values in the code to avoid having
the user input it or to avoid having to read it from
a file
ArrayName =
Array (10, 20, 30)
Operators
/ -
\ -
Integer division (truncates the answer)
^ -
Exponentiation operator
* -
Multiply
+ -
Plus
- -
Minus
= -
Equal
> -
Greater Than
< -
Less Than
<>
- Not Equal
>=
- Greater than or equal
<=
- Less than or equal
AND -
Defines a boolean value that is the AND of two values
result =
expression1 AND expression2
OR -
Defines a boolean value that is the OR of two values
result =
expression1 OR expression2
IS -
Determines if 2 variables reference the same object
result =
object1 IS object2
LIKE -
Determines if one string matches a pattern
result =
string LIKE pattern
More about operators (MSDN).
Math
Math.Round - Rounds a number to a selectable number of
decimal places
result = Math.Round
( tempvariable,2 )
·
Called
Round in VB6
result = Math.Round ( tempvariable,2 )
Val - Returns the numerical content of a string
result = Val
("123.4")
Int - Returns an integer by truncating
i = int (
tempvariable )
Math.Sqrt - Returns the square root of a number
tempvariable1 = Math.Sqrt ( tempvariable2 )
·
Called Sqr
in VB6
tempvariable1 = Math.Sqrt ( tempvariable2 )
Math summary (MSDN).
Type Conversions
CBool, CByte, CCur, CDate, CDbl,
CDec, CInt, CLng, CSng, CStr, Cvar
See documentation
(MSDN).
Strings
VB 6:
Str – Returns a string representation of a number.
VB.Net
value.ToString() returns the string representation of value
Left -
Returns the left n characters of a string
temp = Left
( teststring, 4 )
Right
- Returns the right n characters of a string
temp = Right
( teststring, 4 )
Trim -
Removes leading and trailing spaces of a string
temp = Trim
( teststring )
LTrim
- Removes only the leading spaces of a string
temp = LTrim
( teststring )
RTrim
- Removes only the trailing spaces of a string
temp = Rtrim
( teststring )
UCase
- Makes all characters upper case
temp = Ucase
( teststring )
LCase
- Makes all characters lower case
temp = Lcase
( teststring )
Mid -
Returns n characters from a string, starting a any position
temp = Mid
( teststring, 1, 4 )
Len -
Returns the length of a string (how many characters it has)
temp = Len
( teststring )
VB.Net:
Can also use temp =
teststring.Length
LSet -
Positions a string inside another, flush to the left
temp =
lset ( teststring )
RSet -
Positions a string inside another, flush to the right
temp =
rset ( teststring )
Format
- Returns a string formatted according to a user-defined format
temp =
format ( teststring, "####.0" )
String
-
temp =
left ( teststring, 4 )
Chr -
Returns the string representation of a number
temp = str
( 32 )
Asc -
Returns the ASCII code of a single character
temp = asc
( "A" )
Space
- Returns n spaces
temp =
space ( 15 )
Instr
- Determines if one string is found within a second string
i = Instr (starthere, string1,
string2)
InStrRev
- Determine if one string is found in a second, starting at the end
i = InStrRev (string1, string2,
start)
StrComp
- Compares two strings
result =
StrComp (string1, string2)
StrConv
- Converts the case of a string's characters
StrConv (string, vbuppercase)
StrReverse
- Reverses character order in a string
StrReverse (string1)
Replace
- Replaces each occurrence of a string
Replace (bigstring,
searchstring, replacementstring)
String
function examples (MSDN)
Boolean
Expressions (MSDN)
Misc
MsgBox
- A built-in dialog box that gives a message and allows a user input
x = msgbox "Read this!", vbokonly, "Test Message"
The result of which button the
user clicked is saved in x.
InputBox
- A built-in dialog box that allows entry of a text string
inputbox
"Input a value!", 5
VB 6:
Load - Load an object
load form1
Unload - Unload an object
Unload
form1
RGB -
Returns a color value by inputting the red, green, and blue parts
form1.backcolor = RGB
(12,128,256)
Me -
Refers to the current object, usually the active form
VB 6 print Me.caption
VB.Net Debug.WriteLine(Me.Text)
Loops and Conditional Decisions
If..Then..Else - Performs code based
on the results of a test
If A>5 Then Print "A is
a bit number!"
For...Next
- Loops a specified number of times
For i = 1 to 5: print #1, i:
next i
For Each ... Next - Walks through a collection
For Each X in Form1.controls:
Next X
While...Wend
- Loops until an event is false
while i
< 5: i = i +1: wend
Select
Case - Takes an action based on a value of a parameter
select case
i
case 1 :
print "it was a 1"
case 2 :
print "it was a 2"
end
select
Do...Loop
- Loops until conditions are met
do while
i < 5 : i = i + 1 : loop
Choose
- Selects and returns a value from a list of arguments
Choose (index, "answer1",
"answer2", "answer3")
With -
Executes a series of statements on a single object
With textbox1
.Height = 100
.Width = 500
End With
End -
Immediately stops execution of a program
End
Stop -
Pauses execution of a program (can restart without loss of data)
Stop
VB6 Tips
Use Debug.Print to print out
data values. Results are shown in the Immediate window
while the program is running
Debug.Print
varName1, varName2, …, varNameN
Make VB save your program when you
run it
Tools->Options->Environment
tab
In the "When a program starts", chose either "Save
Changes" or "Prompt to Save Changes"
VB.Net tips
Use Debug.WriteLine
to print out data values. Results are shown in the Output window while the
program is running. You must pass WriteLine a string, so compose the string by concatenating
other strings using the + operator.
Example: Debug.WriteLine("Value of x: " + x.ToString)