learn visual basic -- 4.1, variables and operators

here, we are going into a fundamental step in programming -- variables. variables determine how much memory, or RAM (random access memory) your program needs from the computer. they are also "containers" which hold information for the program, be it input or output.

if you followed my articles closely, try to remember this:

greeting = txt1.txt

the word greeting is a variable. it is not enclosed by quots. it is simply a word which could, preferably, be identified with what value it holds. for example, the varable greeting here, will contain a string value (a sentence enclosed by quots, see previous chapter), which is actually a greeting for the Hello World program when the user clicks on the greet button.

the operator, =, assigns the value of txt1.text, which is the value of the property text of the textbox, to the variable greeting. so far so good. then, consider another situation:

answer = 1 + 1

arithmathically, answer equals to 2. and correct! answer is really 2. the variable, answer, is assigned the value of 1 + 1, which is 2. the operator, +, adds the values together. you can guess that:

- for subtract
/ for divide
* for multiply

and it is true for all integer values (numbers and decimals, both negative and positive). note that integer values are not between quots. if not, check this:

var1 = "1" + "1"
var2 = "1 + 1"

the value of var1, a variable, is "11". this is a string. the quots forced the program to read the numbers "1" as a string and the operator + joins the two together forming the string value "11".

for var2, the value it is assigned is "1 + 1" as it is. because the whole expression is in quots which means it is a string. a string always appears as it is and is not affected by operators.

however consider these:

var3 = "1" - "1"
var4 = "1" / "1"

var3 is definitely not "0" and var4 is ridiculous. you cannot take a sentence and divide it by another sentence. your maths teacher didn't teach you this.

for the plus sign (+) in var1, it acts as a concatenation operator, joining two strings or more together. however a better or rather professional way is to use the ampersand (&). you can try this: below:

create a new project (see preivous chapters if you don' know how). then create a command button on the form. change the properties to:

commandbutton1
name -- cmd1
caption -- click me

form1
name -- frm1
caption -- My VB program

double click on the command button and type in the following code:

Private Sub cmd1_Click()
var1 = "I am a number "
var2 = 1
var3 = "Visual Basic "
var4 = "programmer!"
message = var1 & var2 & var3 & var4
MsgBox message, , var2
End Sub

run the program by clicking on the run sub/userform button on the tool bar. click on "click me" and a message box comes up shows the message "I am a Visual Basic programmer!" and the title is "Visual Basic". notice how we used variables in the MsgBox funtion. yes, a function. i'll talk about functions in intermediate stages.

all the variables we just discussed are not declared explicitly. they are used, because you happen to need one only here in the program, you probably did not plan to have it. but what if you planned to have a variable that can only take some values? you declare it by using the dim key word like this:

dim variable

what if you want it to take only a particular value?

dim variable as type

the as type keyword or phrase is used to define and restrict the value of the variable. this would ensure that the value type will not be changed by other procedures accidentally and cause an error in the program. try this:

Private Sub cmd1_Click()
Dim var1 As String
Dim var2 As Integer
Dim var3 As String, var4 As String
var1 = "I am a number "
var2 = 1
var3 = " Visual Basic "
var4 = "programmer!"
message = var1 & var2 & var3 & var4
MsgBox message, , var3
End Sub

notice that you can declare, with the dim keyword, one variable on each line or, a series of variables on one line separated by commas. also not that even when the variables on a single lines carries the same value type, you still have to enter the as type keyword for every variable on that line and not:

Dim var3, var4 As String

in this case, only var4 is of String type and var3 can contain any type of information. using the Dim statement is advantages as it allocates memory for you program to prevent memory shortages. other types include:

As Boolean
true or false. any value not 0 is true (except negative numbers) and 0 is false.

As Double
a decimal number.

As Float
a decimal number also, but smaller than Double and requires less memory than Double.

continue next chapter