1.3 Perl Variables (Scalars)

 

Every programming language handles variables differently. In C++ or Java you must declare your variable along with its type. For example:

 

int length; <br> int width; <br> char name[50];

 

would allow you to store an integer in length and width and a name up to 50 characters under name. It would not be possible to say something like:

length = "CS 290W"; <br> name = 500;

 

Why? Because length only accepts numbers and name only accepts characters. In Perl you can forget all those "nasty" type declarations because you do not have int, float, String, char, etc. Instead you have what is known as a scalar variable.

Scalars can contain all types of data. Floats, Strings, Integers, etc to name a few. Although their variable names stay constant throughout the program, a variable may contain an Integer at one point and then a String at another. For this reason it is VERY important to comment Perl scripts well, because can occasionally get a bit confusing.

Scalars begin with a dollar sign and then the variable name. Below are a few examples of scalar variables under Perl:

$Name
 $Bob_Age <br> $Size_At_1

Scalar variables MUST begin with a letter after the dollar sign. After that you may choose whether to use letters, numbers, or underscores. The following are illegal:

$1_Name <br> $2_Bob_Age <br> $3_Size_At_1

Please take particular caution when choosing variable names. A variable such as $a2b3c4 is not very helpful to someone reading your code. But, $Matrix_Rows is helpful.

You may want to also keep track of your variable types. One popular method is known as Hungarian Notation. What this means is that you start every variable with one or two lowercase characters describing its type. For example see if you can tell what type of data the following variables hold:

<font color="#FF0000">$iAge <br> $sName<br> $fDivide</font>

Hopefully you might have guessed that $iAge is an Integer, $sName is a String, and $fDivide is a floating point variable. Using Hungarian Notation will greatly help you in debugging your code by allowing you to distinguish different variable types. Although Perl allows you to do the following...

$sName = "Dave";
$sName = 100;

...we strongly suggest you NOT do that. Instead, create a new variable to hold the integer type to avoid further confusion later on in your program.

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