Fundamentals of Programming: Variables
||From this point on we are going to drop the
Let's take a look at this program:
1 Dim name As String 2 Dim age As Integer 3 name = "Peter" 4 age = 29 5 Console.WriteLine("Hello " & name & " you are " & age & " years old") 6 Console.WriteLine("This also means you are " & age * 12 & " months old") 7 Console.WriteLine("Bye " & name & "!") 8 Console.ReadLine()
you might be expecting it to print out:
Hello name you are age years old
But instead it says:
What a friendly program! Let's break it down line by line:
dimis a variable declaration, creating a temporary data store, a variable, and calling it
nameIt also makes sure that whatever goes into
namewill be a string by setting it to
- We declare another variable called
ageand make sure it is stored as an integer (a whole number)
- The variable name that we created earlier is now assigned a value and as it's a string we better use speech marks - "Peter"
- The variable age that we created earlier is now assigned a value and as it's an integer we better not use speech marks - 29
- This line writes things to the screen, starting with the text
"Hello "which attaches that variable we saw earlier to, but instead of putting the variable name, it puts the contents of the variable ("Hello Peter"), then it attaches some more text ("Hello Peter you are ") and adds another variable, age. Even though age is an integer we can stick it together with a string ("Hello Peter you are 29"). Then finally it uses the ampersand once more to attach the final piece of text ("Hello Peter you are 29 years old)
- This line works in pretty much the same way, but it does a calculation, working out the age in months. Computers are like giant calculators and you can perform all the sums you can perform on your little pocket calc performed and far far more using them!
- The great things about variables is that we can use them again and again, here we say "Bye " and using an ampersand stick on the name of the person. This is great, by using a variable we only need to write "Peter" once and save it as
name. If someone else came along and wanted to change the program they just need to change the value of
name. Programming is all about being as lazy as possible.
- Good old
console.readline()stops the screen disappearing too fast
What you have just seen is a declaration of two variables, name and age. A variable is a known or unknown value that has been given a symbolic name. This allows the name to be used independently of the value. It is advisable that a meaningful name for readability and convenience. This name is known as the identifier. To declare a variable in VB.NET we do the following:
Dim identifierName As datatype
Most programming languages have rules about identifiers: they generally have to use only Alphanumeric characters (a..Z0..9) and some languages are case sensitive (name != Name).
Once you have declared a variable you need to assign it a value. Assignment, in programming terms, is the giving of a value to a variable, for example:
identifierName = 7
Here we are assigning the value
7 to the variable
identifierName, so when we use
identifierName, we mean the value
1 dim identifierName as integer 2 identifierName = 7 3 console.writeline("The value stored in identifierName is: " & identifierName)
1 dim name as string 2 dim age as integer 3 name = "Syeda" 4 age = 31 5 console.writeline("Hello " & name & " you are " & age & " years old") 6 console.writeline("This also means you are " & age * 12 & " months old") 7 console.writeline("This also means you are " & age * 365 & " days old") 8 console.writeline("This also means you are " & age * 365 * 24 & " hours old") 9 console.writeline("This also means you are " & age * 365 * 24 * 60 & " minutes old") 10 console.writeline("This also means you are " & age * 365 * 24 * 60 * 60 & " seconds old") 11 console.writeline("Bye " & name & "!") 12 console.readline()
To keep track of a changing value that is used in many places but only needs to be updated in one.
A couple of things to note here: