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📚 ASP – VB Functions – Use Built-In VBScript Functions in Classic ASP

🧲 Introduction – What Are VB Functions in Classic ASP?

VBScript functions in Classic ASP are predefined utility methods that simplify common programming tasks—such as string manipulation, math, date formatting, and type conversion. These built-in functions are executed on the server side, making Classic ASP powerful and efficient for dynamic page generation.

🎯 In this guide, you’ll learn:

Most-used VBScript functions in Classic ASP
Syntax and behavior of string, date, math, and conversion functions
How to use them in real-world ASP applications
Output examples and best practices

🔤 String Functions

Function	Description	Example
`Len(string)`	Returns the length of a string	`Len("ASP")` → 3
`LCase(string)`	Converts to lowercase	`LCase("HELLO")` → “hello”
`UCase(string)`	Converts to uppercase	`UCase("asp")` → “ASP”
`Trim(string)`	Removes leading and trailing spaces	`Trim(" asp ")` → “asp”
`Left(str, n)`	Returns the leftmost n characters	`Left("Hello", 2)` → “He”
`Right(str, n)`	Returns the rightmost n characters	`Right("Hello", 2)` → “lo”
`Mid(str, start, length)`	Extracts substring from position	`Mid("Classic", 2, 3)` → “las”
`Replace(str, find, replace)`	Replaces substrings	`Replace("dog", "d", "l")` → “log”
`InStr(string1, string2)`	Finds position of substring	`InStr("Hello", "e")` → 2

🔢 Math Functions

Function	Description	Example
`Abs(number)`	Absolute value	`Abs(-5)` → 5
`Sqr(number)`	Square root	`Sqr(25)` → 5
`Int(number)`	Returns integer part of a number	`Int(7.8)` → 7
`Rnd()`	Returns random number between 0 and 1	`Rnd()` → 0.534 (example)
`Round(number)`	Rounds to nearest whole number	`Round(2.6)` → 3
`Fix(number)`	Truncates decimal part	`Fix(-3.5)` → -3

🗓️ Date & Time Functions

Function	Description	Example
`Now()`	Current date and time	`Now()` → 06/11/2025 04:15:32 PM
`Date()`	Current date only	`Date()` → 06/11/2025
`Time()`	Current time only	`Time()` → 04:15:32 PM
`DateAdd(interval, number, date)`	Adds time to a date	`DateAdd("d", 5, Date())` → +5 days
`DateDiff(interval, date1, date2)`	Difference between two dates	`DateDiff("d", "06/01/2025", Date())`
`Day(date)`	Extracts day of the month	`Day(Date())` → 11
`Month(date)`	Extracts month	`Month(Date())` → 6
`Year(date)`	Extracts year	`Year(Date())` → 2025

🔁 Conversion Functions

Function	Description	Example
`CInt(expr)`	Converts to integer	`CInt("5")` → 5
`CLng(expr)`	Converts to long integer	`CLng("1000")` → 1000
`CSng(expr)`	Converts to single-precision float	`CSng("12.5")` → 12.5
`CDbl(expr)`	Converts to double-precision float	`CDbl("3.1415")` → 3.1415
`CStr(expr)`	Converts to string	`CStr(100)` → “100”
`IsNumeric(expr)`	Checks if value is numeric	`IsNumeric("123")` → True
`TypeName(expr)`	Returns the type name of a variable	`TypeName(100)` → “Integer”

📥 Example – Combine VB Functions in ASP

<%
Dim name, age, birthday, today, years

name = " Alice "
age = "30"
birthday = "06/11/1995"
today = Date()
years = DateDiff("yyyy", birthday, today)

Response.Write "Welcome, " & Trim(name) & "!<br>"
Response.Write "Age from input: " & CInt(age) & "<br>"
Response.Write "You are approximately " & years & " years old."
%>

🧪 Output:

Welcome, Alice!  
Age from input: 30  
You are approximately 30 years old.

📘 Best Practices for VB Functions in ASP

✅ Do:

Use Trim, UCase, CInt, etc., when processing form input
Use IsNumeric and TypeName for safe data conversion
Combine DateDiff and Now() for logs or age calculations

❌ Avoid:

Using CInt on empty strings or non-numeric values (causes errors)
Ignoring case when comparing input (use LCase() for safety)
Skipping type conversion before math operations

📌 Summary – Recap & Next Steps

Classic ASP comes with a rich set of VBScript functions for strings, numbers, dates, and type handling. Knowing when and how to use them makes your server-side scripts clean, robust, and efficient.

🔍 Key Takeaways:

Len, UCase, and Replace help clean and format strings
CInt, IsNumeric, and CStr are vital for user input
DateDiff and Now() help you calculate durations and timestamps

⚙️ Real-world Use Cases:

User registration and form processing
Logging timestamps for auditing
Formatting invoices and messages

❓ FAQs – ASP VB Functions

❓ Are VBScript functions built into Classic ASP?
✅ Yes. Classic ASP uses the VBScript engine, so these functions are built-in.

❓ Can I create custom functions too?
✅ Absolutely. Use Function and Sub in ASP to define your own.

❓ Do VBScript functions work in client-side HTML?
❌ No. VBScript functions run on the server, not in the browser.

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