Today's Goals

Understand variables
Know the common data types
Declare and use variables
Understand scope

Key Concepts

1. Declaring Variables

A variable is a name for a value you can read and change while the code runs. VBA declares variables with Dim:

vba
Dim variableName As DataType

Names start with a letter (Chinese characters work too) and take no spaces, periods, or reserved words. Option Explicit at the top of a module forces declaration before use — keep it on.

2. Common Data Types

Data Type	Description	Example
Integer	Whole numbers (-32,768 to 32,767)	Dim i As Integer
Long	Long integer (about ±2.1 billion)	Dim l As Long
String	Text	Dim s As String
Double	Double-precision floating point	Dim d As Double
Boolean	True / False	Dim b As Boolean
Date	Dates and times	Dim dt As Date

Rules of thumb: Long for whole numbers, Double for money and decimals; date literals go between hash marks, e.g. #1999-1-1#. An untyped variable becomes a Variant — avoid that when you can.

3. Assignment, Concatenation, and Conversion

= assigns, & joins strings and numbers, vbCrLf breaks a line, and a trailing _ continues a statement. Cell and InputBox values arrive as text — convert before doing math: CInt, CDbl, CStr, Val.

4. Variable Scope

Procedure-level: Dim inside a procedure — visible only there, gone when it ends
Module-level: Dim at the top of a module — visible to that module's procedures
Global: Public at the top of a module — visible to the whole project

Use the smallest scope that works.

Today's Code

vba
Sub 变量示例()
    ' Declare variables
    Dim name As String
    Dim age As Integer
    Dim price As Double
    Dim isStudent As Boolean

    ' Assign values
    name = "张三"
    age = 25
    price = 99.5
    isStudent = True

    ' Use them
    MsgBox "姓名: " & name & vbCrLf & _
           "年龄: " & age & vbCrLf & _
           "价格: " & price
End Sub

Real-World Scenario

The setup: a sales rep quotes an order — unit price 199.9, three units at 20% off, payable amount exact to the cent.

vba
Sub 计算订单金额()
    Dim 单价 As Double, 数量 As Long, 折扣 As Double, 应付 As Double

    单价 = 199.9
    数量 = 3
    折扣 = 0.8

    应付 = 单价 * 数量 * 折扣
    MsgBox "应付金额: " & Format(应付, "0.00") & " 元"
End Sub

Result: 199.9 × 3 × 0.8 = 479.76. Format(应付, "0.00") forces two decimal places so no floating-point tail shows, and a later price or discount change touches only the assignment lines — that is why variables beat hard-coded numbers.

Exercises

Declare variables that store your name and age
Write a program that adds two numbers
Try variables of different data types

Exercise Solutions

Declare with Dim — Dim name As String, age As Integer — then assign each.
Declare two numeric variables, run sum = a + b, and show the result with MsgBox.
Declare Integer, String, Boolean, and Date variables, assign values, and watch what each holds.

Extension Exercises

Ask for a birth year with InputBox, then calculate and show the age (Year(Date) gives the current year).
Swap two variables through a temporary variable.

Common Errors and Troubleshooting

Error / Symptom	Cause	Fix
`Run-time error '13': Type mismatch`	Non-numeric text assigned to a numeric variable	Check the source; convert with Val/CInt
`Compile error: Variable not defined`	Undeclared or misspelled variable	Add a Dim; check the spelling
Two "numbers" concatenate instead of adding	The cell values are text	Convert with `Val()` before calculating

Summary

Declare first, pick the right type, keep the scope tight — and convert cell data before doing math on it.

由在线工具箱(www.vba.net)整理制作

🌱 Day02 - Variables and Data Types