ASP Tutorials - Lesson 8: Procedures and Functions

	Procedures and Functions

Introduction to Procedures

Procedures

One of the techniques used for effective programming is to divide a big assignment in (relatively small) sub-assignments. Each sub-assignment is meant to (possibly completely) solve a particular problem so that other sub-assignments of the program can simply request its result or refer to it when necessary. Such a sub-assignment is called a procedure. There are two categories of procedures you will use in your programs: those that have already been created thus made available to you, and those you will create yourself.

Some languages like VBScript and Pascal consider that there are two types of procedures: functions and sub routines (some other languages like C++ and C# don't explicitly differentiate both categories).

Practical Learning: Introducing Sub Procedures

Start Notepad or your text editor and type the following:

<%@ Language="VBScript" %>
<html>

<head>

<title>Geometry: The Square</title>
</head>

<body>

<h1>Geometric Figures: The Square</h1>
<p>A square is a geometric figure made of 4 equal sides joined at their ends to
form 4 right angles.</p>

<form action="square2.asp" method="get">
  <table border="0" width="316">
    <tr>
      <td width="109">Side:</td>
      <td width="52"><input type="text" name="txtSide" size="14"
        value = <% =Request.QueryString("txtSide") %> >
      </td>
      <td width="68"><input type="submit" value="Calculate" name="btnCalculate"></td>
      <td width="67"><input type="reset" value="Restart" name="btnReset"></td>
    </tr>
  </table>
</form>

</body>

</html>

Save the file as square2.asp in your Geometry and Algebra folder (from Lesson 4)
To preview it, open your browser and change the address to http://localhost/geometry/square2.asp
Return to Notepad

Introduction to Sub-Procedures

A sub procedure is an assignment that is carried but doesn't give back a result. To create a sub procedure, you start the section with the Sub keyword followed by a name (like everything else, a procedure must have a name). The name of a procedure is always followed by parentheses. At the end of the sub procedure, you must type End Sub. Therefore, the formula of a sub procedure is:

Sub ProcedureName()

End Sub

The name of a procedure follows the same rules we reviewed for variables. In addition, there are some suggestions you can use when naming your procedures:

If the procedure performs an action that can be represented with a verb, you can use that verb to name it. Here are examples: show, display
To make the name of a procedure stand, you should start it in uppercase. Examples are Show, Play, Dispose, Close
You should use explicit names that identify the purpose of the procedure. If a procedure would be used as a result of another procedure, reflect it on the name of the sub procedure. Examples would be: afterupdate, longbefore.
If the name of a procedure is a combination of words, you should start each word in uppercase. Examples are: AfterUpdate, SayItLoud

On the right side of the name of the procedure, you can add parentheses or omit them. The section between the Sub and the End Sub lines is referred to as the body of the procedure. Here is an example:

<%
Sub ShowFullName

End Sub
%>

The body of the procedure is used to define what assignment and how the assignment should be carried. For example, if you need to use a variable, you can declare it and specify the kind of variable you need. There is no restriction on the type of variables that can be declared in a procedure. Here is an example in which a variable is declared in the body of a sub routine:

<%
Sub ShowFullName
  Dim FirstName
End Sub
%>

In the same way, you can declare as many variables as you need inside of a procedure. The actions you perform inside of a procedure depend on what you are trying to accomplish. For example, a procedure can simply be used to create a string. The above procedure can be changed as follows:

<%
Sub ShowFullName
  Dim FirstName
  Dim LastName
  Dim FullName

  FirstName = "Paul"
  LastName  = "Motto"
  FullName  = LastName & ", " & FirstName
  Response.Write("Person Name: " & FullName)
End Sub
%>

Practical Learning: Creating a Sub Procedure

To create a sub procedure, change the file as follows:

<%@ Language="VBScript" %>
<html>

<head>

<title>Geometry: The Square</title>
</head>

<body>

<h1>Geometric Figures: The Square</h1>
<p>A square is a geometric figure made of 4 equal sides joined at their ends to
form 4 right angles.</p>

<form action="square2.asp" method="get">
  <table border="0" width="316">
    <tr>
      <td width="109">Side:</td>
      <td width="52"><input type="text" name="txtSide" size="14"
        value = <% =Request.QueryString("txtSide") %> >
      </td>
      <td width="68"><input type="submit" value="Calculate" name="btnCalculate"></td>
      <td width="67"><input type="reset" value="Restart" name="btnReset"></td>
    </tr>
  </table>
</form>

<%
' This procedure is used to calculate and display
' the perimeter of a square based on the side from the form
Sub SquarePerimeter()
    Dim dblSide
    Dim dblPerimeter

    ' Get the measure of the side from the form
    dblSide = Request.QueryString("txtSide")
    ' Calculate the perimeter
    dblPerimeter = dblSide * 4
    ' Display the perimeter in the browser
    Response.Write("Perimeter: " & dblPerimeter & "<br>") 
End Sub

' This procedure is used to calculate and display
' the area of a square based on the side from the form
Sub SquareArea
    Dim dblSide
    Dim dblArea

    ' Get the measure of the side from the form
    dblSide = Request.QueryString("txtSide")
    ' Calculate the area
    dblArea = dblSide * dblSide
    ' Display the are in the browser
    Response.Write("Area:      " & dblArea) 
End Sub
%>
</body>

</html>

Save the file

Sub Procedure Call

Once you have a procedure, whether you created it or it is part of VBScript, you can use it. Using a procedure is also referred to as calling it. Before calling a procedure, you should first locate the section of code in which you want to use it. To call a simple procedure, simply type its name in the section where you want to use. Here is an example:

<%
Sub ShowFullName
  Dim FirstName
  Dim LastName
  Dim FullName

  FirstName = "Paul"
  LastName  = "Motto"
  FullName  = LastName & ", " & FirstName
  Response.Write("Person Name: " & FullName)
End Sub
%>

<% ShowFullName %>

You add or omit parentheses on the right side of the name of the procedure when calling it.

Practical Learning: Calling a Sub Procedure

To call a procedure, change the file as follows:

<%@ Language="VBScript" %>
<html>

<head>

<title>Geometry: The Square</title>
</head>

<body>

<h1>Geometric Figures: The Square</h1>
<p>A square is a geometric figure made of 4 equal sides joined at their ends to
form 4 right angles.</p>

<form action="square2.asp" method="get">
  <table border="0" width="316">
    <tr>
      <td width="109">Side:</td>
      <td width="52"><input type="text" name="txtSide" size="14"
        value = <% =Request.QueryString("txtSide") %> >
      </td>
      <td width="68"><input type="submit" value="Calculate" name="btnCalculate"></td>
      <td width="67"><input type="reset" value="Restart" name="btnReset"></td>
    </tr>
  </table>
</form>

<%
' This procedure is used to calculate and display
' the perimeter of a square based on the side from the form
Sub SquarePerimeter()
    Dim dblSide
    Dim dblPerimeter

    ' Get the measure of the side from the form
    dblSide = Request.QueryString("txtSide")
    ' Calculate the perimeter
    dblPerimeter = dblSide * 4
    ' Display the perimeter in the browser
    Response.Write("Perimeter: " & dblPerimeter & "<br>") 
End Sub

' This procedure is used to calculate and display
' the area of a square based on the side from the form
Sub SquareArea
    Dim dblSide
    Dim dblArea

    ' Get the measure of the side from the form
    dblSide = Request.QueryString("txtSide")
    ' Calculate the area
    dblArea = dblSide * dblSide
    ' Display the are in the browser
    Response.Write("Area:      " & dblArea) 
End Sub
%>

<% SquarePerimeter %>

<% SquareArea() %>
</body>

</html>

Save the file
Return to the browser and refresh it
Type a value as the side of the square and click Calculate
Return to your text editor

Server-Side Processing

So far, we wrote our procedures in the same file that request the values being processed. Another way you can perform this type of job, as we saw in Lesson 4, is to divide the assignment among different files. For example, you can write your code in one file that would request some values from the user. Once the user clicks the sending button, another file would receive the values and process them. This second file can then optionally display the values to the user or it can send the value to another file. Everything is done as you see fit. Perhaps planning is one of the most important aspects of implementing this type of scenarios.

Practical Learning: Using Various Files

Start a new file in your text editor and type the following:

<%@ Language="VBScript" %>
<html>

<head>

<title>Geometry: The Circle</title>
</head>

<body>

<h1>Geometric Figures: The Sphere</h1>
<p>Based on the radius you provided, the results of your circle are:</p>

<%

Function Diameter()
  Dim Radius

  Radius = CDbl(Request.QueryString("txtRadius"))
  Diameter = Radius * 3.14159
End Function

Function Circumference
  Dim Radius

  Radius = CDbl(Request.QueryString("txtRadius"))
  Circumference = Radius * 2 * 3.14159
End Function

Function Area
  Dim Radius

  Radius = CDbl(Request.QueryString("txtRadius"))
  Area = Radius * 2 * 3.14159
End Function
%>

<table border="0" width="316">
  <tr>
    <td width="109">Radius:</td>
    <td width="52"><input type="text" name="txtRadius" size="14"
        value='<%= Request.QueryString("txtRadius") %>' >
    </td>
    <td width="135"></td>
  </tr>
  <tr>
    <td width="109">Diameter:</td>
    <td width="52"><input type="text" name="txtDiameter" size="14"
        value='<% =Diameter() %>' >
    </td>
    <td width="135"></td>
  </tr>
  <tr>
    <td width="109">Circumference:</td>
    <td width="52"><input type="text" name="txtCircumference" size="14"
        value='<% =Circumference() %>' >
    </td>
    <td width="135"></td>
  </tr>
  <tr>
    <td width="109">Area:</td>
    <td width="52"><input type="text" name="txtArea" size="14"
        value='<% =Area() %>' >
    </td>
    <td width="135"></td>
  </tr>
</table>

<p><a href="circle2.asp">Return</a></p>

</body>

</html>

Save it as circleresults2.asp in your Geometry and Algebra folder

Start a new file and type the following:

<html>

<head>

<title>Geometry: The Circle</title>
</head>

<body>

<h1>Geometric Figures: The Circle</h1>
<p>A circle is a geometric figure made of various points with the following
rules:</p>

<ul>
  <li>There is a point of this figure called the Center</li>
  <li>All points that form the circle are positioned at an equal distance from
    the center</li>
</ul>

<form action="circleresults2.asp" method="get">
  <table border="0" width="316">
    <tr>
      <td width="109">Radius:</td>
      <td width="52"><input type="text" name="txtRadius" size="14" value="0.00">
      </td>
      <td width="68"><input type="submit" value="Submit" name="btnSubmit"></td>
      <td width="67"><input type="reset" value="Reset" name="btnReset"></td>
    </tr>
  </table>
</form>

</body>

</html>

Save it as circle2.asp in your Geometry and Algebra folder
Access your browser and change its address to http://localhost/geometry/circle2.asp
Press Enter and type a number, such as 28.46, in the Radius text box
Click Calculate
Return to your text editor

Arguments and Parameters

Introduction

So far, to use a value in a procedure, we had to declare it. In some cases, a procedure may need an external value in order to carry its assignment. A value that is supplied to a procedure is called an argument.

When creating a procedure that will use an external value, declare the argument that represents that value between the parentheses of the procedure. For a sub routine, the formula you use would be:

Sub ProcedureName(Argument)
      
End Sub

The argument must be declared as a normal variable, omitting only the Dim keyword. Here is an example that creates a function that takes a string as argument:

<%
Sub ShowFullName(FirstName)
 
End Sub
%>

A certain procedure can take more than one argument. In this case, in the parentheses of the procedure, separate the arguments with a comma. Here is an example of a sub routine that takes two arguments:

<%
Sub ShowFullName(FirstName, LastName)
  Dim FullName

  FullName  = LastName & ", " & FirstName
  Response.Write(FullName)
End Sub
%>

In the body of a procedure that takes one or more arguments, use the argument(s) as you see fit as if they were locally declared variables. For example, you can involve them with values inside of the procedure. You can also exclusively use the values of the arguments to perform the assignment.

Calling a Procedure With Argument

If you or someone else created a procedure you want to use in your code, when calling it, make sure you provide a value for that argument. The way you call this procedure depends on some factors such as whether the procedure is a sub or a function, the number of arguments.

To call a sub procedure that takes only one argument, you can type its name followed by space, and followed by the value of the argument. If you have that value, you can provide it. If the value is a number and you have the number already, you can type it after the name of the procedure. If the value is a string, make sure you provide it in double-quotes. Here is an example:

<%
Sub ShowCountryName(Name)
  Response.Write(Name)
End Sub
%>

<% ShowCountryName "Emirats Arabes Unis" %>

This would produce:

As an alternative, when calling a sub procedure you can precede it with the Call keyword. In this case, the argument(s) must be passed in parentheses. With this technique, the above procedure would be called as follows:

<%
Sub ShowCountryName(Name)
  Response.Write(Name)
End Sub
%>

<% Call ShowCountryName("Emirats Arabes Unis") %>

You can also pass the name of a variable that holds the string to be passed as argument. Here is an example:

<%
Sub ShowCountryName(Name)
  Response.Write(Name)
End Sub
%>

<%
  Dim CName

  CName = "Mexico"
  ShowCountryName CName
%>

If you are calling a sub procedure that takes more than one argument, when passing the arguments, separate them with a comma. If you know the values to be passed as argument when you call the procedure, provide each value. Here is an example:

<%
Sub ShowFullName(FirstName, LastName)
  Dim FullName

  FullName  = LastName & ", " & FirstName
  Response.Write(FullName)
End Sub
%>

<% ShowFullName "Beltrami", "Ramirez" %>

If the values are numbers, provide their values. If you use a mix of values, because VBScript doesn't provide a mechanism to identify the values, it is your responsibility to make sure that each value is properly passed.

Functions

Introduction

Like a sub procedure, a function is used to perform an assignment. The main difference between a sub procedure and a function is that, after carrying its assignment, a function gives back a result. We also say that a function "returns a value". To distinguish both, there is a different syntax you use for a function.

Practical Learning: Introducing Function

Start a new file in your text editor and type the following:

<%@ Language="VBScript" %>
<html>

<head>

<title>Rectangle</title>
</head>

<body>

<h1>Geometric Figures: The Rectangle</h1>
<form method="GET" action="rectangle1.asp">
  <table border="0" width="276">
    <tr>
      <td width="79">Length:</td>
      <td width="105"><input type="text" name="txtLength" size="12"
        value = <%=Request.QueryString("txtLength")%> ></td>
      <td width="72"></td>
    </tr>
    <tr>
      <td width="79">Height:</td>
      <td width="105"><input type="text" name="txtHeight" size="12"
       value = <%=Request.QueryString("txtLength")%> ></td>
      <td width="72"><input type="submit" value="Submit" name="B1"></td>
    </tr>
    <tr>
      <td width="79">Perimeter:</td>
      <td width="105"><input type="text" name="txtPerimeter" size="12"
        value = "0.00" ></td>
      <td width="72"></td>
    </tr>
    <tr>
      <td width="79">Area:</td>
      <td width="105"><input type="text" name="txtArea" size="12"
        value = "0.00" ></td>
      <td width="72"><input type="reset" value="Reset" name="B2"></td>
    </tr>
  </table>
</form>

</body>

</html>

Save the file as rectangle1.asp in your Geometry and Algebra folder (from Lesson 4)
To preview it, open your browser and change the address to http://localhost/geometry/rectangle1.asp
Return to Notepad

Function Creation

To create a function, you use the Function keyword followed by a name and parentheses. Based on this, the minimum formula used to create a function is:

Function FunctionName()
    
End Function

The name of a function follows the same rules and suggestions we reviewed for sub procedures. As mentioned already, the section between the Function and the End Function lines is the body of the function. It is used to describe what the function does. As done on a sub procedure, one of the actions you can perform in a function is to declare a (local) variable and use it as you see fit. Here is an example:

<%
Function GetFullName
  Dim FirstName

  FirstName = "Paul"
End Function
%>

After performing an assignment in a function, to indicate the value it returns, somewhere after the assignment and before the End Function line, type the name of the function, followed by the assignment operator "=" , followed by the value the function returns. Here is an example:

<%
Function GetFullName
  Dim FirstName
  Dim LastName

  FirstName = "Paul"
  LastName  = "Motto"
  GetFullName = LastName & ", " & FirstName
End Function
%>

You can also use some local variables in the function to perform an assignment and then assign their result to the name of the function. Here is an example:

<%
Function GetFullName
  Dim FirstName
  Dim LastName
  Dim FullName

  FirstName = "Paul"
  LastName  = "Motto"
  FullName  = LastName & ", " & FirstName
  GetFullName = FullName
End Function
%>

Practical Learning: Creating a Function

To create a function, type the following in the file:

<%@ Language="VBScript" %>
<html>

<head>

<title>Rectangle</title>
</head>

<body>

<h1>Geometric Figures: The Rectangle</h1>
<form method="GET" action="rectangle1.asp">
  <table border="0" width="276">
    <tr>
      <td width="79">Length:</td>
      <td width="105"><input type="text" name="txtLength" size="12"
        value = <%=Request.QueryString("txtLength")%> ></td>
      <td width="72"></td>
    </tr>
    <tr>
      <td width="79">Height:</td>
      <td width="105"><input type="text" name="txtHeight" size="12"
       value = <%=Request.QueryString("txtLength")%> ></td>
      <td width="72"><input type="submit" value="Submit" name="B1"></td>
    </tr>

<%
' This procedure is used to calculate and display
' the perimeter of a rectangle based on the sides from the form
Function RectanglePerimeter()
    Dim dblLength, dblHeight
    Dim dblPerimeter

    ' Get the measures of the length and Height from the form
    dblLength = CDbl(Request.QueryString("txtLength"))
    dblHeight = CDbl(Request.QueryString("txtHeight"))
    ' Calculate the perimeter
    dblPerimeter = (dblLength + dblHeight) * 2
    ' Return the perimeter of the rectangle
    RectanglePerimeter = dblPerimeter
End Function

' This procedure is used to calculate and display
' the area of a square based on the side from the form
Function RectangleArea()
    Dim dblLength, dblHeight
    Dim dblArea

    ' Get the measures of the length and Height from the form
    dblLength = CDbl(Request.QueryString("txtLength"))
    dblHeight = CDbl(Request.QueryString("txtHeight"))
    ' Calculate and return the area of the rectangle
    RectangleArea = dblLength * dblHeight
End Function
%>

    <tr>
      <td width="79">Perimeter:</td>
      <td width="105"><input type="text" name="txtPerimeter" size="12"
        value= "0.00" ></td>
      <td width="72"></td>
    </tr>
    <tr>
      <td width="79">Area:</td>
      <td width="105"><input type="text" name="txtArea" size="12"
        value="0.00" ></td>
      <td width="72"><input type="reset" value="Reset" name="B2"></td>
    </tr>
  </table>
</form>

</body>

</html>

Save the file

Calling a Function

As done for the sub procedure, in order to use a function in your program, you must call it. Like a sub procedure, to call a function, you can simply type its name in the desired section of the program. Here is an example:

<%
Function GetFullName
  Dim FirstName
  Dim LastName
  Dim FullName

  FirstName = "Paul"
  LastName  = "Motto"
  FullName  = LastName & ", " & FirstName
  GetFullName = FullName
End Function
%>

<% Response.Write("Person Name: ") %>
<% =GetFullName %>

Since the primary purpose of a function is to return a value, to better take advantage of such a value, you can assign the name of a function to a variable or to the value attribute of a web control in the section where you are calling the function.

Practical Learning: Calling a Function

To call the functions, change the file as follows:

<%@ Language="VBScript" %>
<html>

<head>

<title>Rectangle</title>
</head>

<body>

<h1>Geometric Figures: The Rectangle</h1>
<form method="GET" action="rectangle1.asp">
  <table border="0" width="276">
    <tr>
      <td width="79">Length:</td>
      <td width="105"><input type="text" name="txtLength" size="12"
        value = <%=Request.QueryString("txtLength")%> ></td>
      <td width="72"></td>
    </tr>
    <tr>
      <td width="79">Height:</td>
      <td width="105"><input type="text" name="txtHeight" size="12"
       value = <%=Request.QueryString("txtLength")%> ></td>
      <td width="72"><input type="submit" value="Submit" name="B1"></td>
    </tr>

<%
' This procedure is used to calculate and display
' the perimeter of a rectangle based on the sides from the form
Function RectanglePerimeter()
    Dim dblLength, dblHeight
    Dim dblPerimeter

    ' Get the measures of the length and Height from the form
    dblLength = CDbl(Request.QueryString("txtLength"))
    dblHeight = CDbl(Request.QueryString("txtHeight"))
    ' Calculate the perimeter
    dblPerimeter = (dblLength + dblHeight) * 2
    ' Return the perimeter of the rectangle
    RectanglePerimeter = dblPerimeter
End Function

' This procedure is used to calculate and display
' the area of a square based on the side from the form
Function RectangleArea()
    Dim dblLength, dblHeight
    Dim dblArea

    ' Get the measures of the length and Height from the form
    dblLength = CDbl(Request.QueryString("txtLength"))
    dblHeight = CDbl(Request.QueryString("txtHeight"))
    ' Calculate and return the area of the rectangle
    RectangleArea = dblLength * dblHeight
End Function
%>

    <tr>
      <td width="79">Perimeter:</td>
      <td width="105"><input type="text" name="txtPerimeter" size="12"
        value= <%=RectanglePerimeter()%> ></td>
      <td width="72"></td>
    </tr>
    <tr>
      <td width="79">Area:</td>
      <td width="105"><input type="text" name="txtArea" size="12"
        value= <%=RectangleArea()%> ></td>
      <td width="72"><input type="reset" value="Reset" name="B2"></td>
    </tr>
  </table>
</form>

</body>

</html>

Save the file
Return to the browser and refresh it
Enter a value for the length and another value for the height
Click Calculate
Return to Notepad

A Function With Arguments

Like a sub procedure, a function can also take one or more arguments. When creating such a function, provide the argument(s) the same way we introduced for the sub procedure. Here is an example:

<%
Function SquareArea(Side)
  SquareArea = Side * Side
End Function
%>

To call a function that takes an argument, you must pass the argument between parentheses. Here is how the above function would be called:

<%
Function SquareArea(Side)
  SquareArea = Side * Side
End Function
%>

<% Response.Write SquareArea(42.58) %>

Just like a sub procedure, a function can take more than one argument. When calling such a function, remember to provide a value for each argument.


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