Dates are always defined using month/day/year format, even if your system is set to display dates in a different format (for example, day/month/year).
If you use a message box to display a date, it's displayed according to your system's short date format. Similarly, a time is displayed according to your system's time format (either 12- or 24-hour). You can modify these system settings by using the Regional Settings option in the Windows Control Panel.
Assignment Statements
An assignment statement is a VBA instruction that evaluates an expression and assigns the result to a variable or an object. Excel's Help system defines expression as “a combination of keywords, operators, variables, and constants that yields a string, number, or object. An expression can perform a calculation, manipulate characters, or test data.”
Much of the work done in VBA involves developing (and debugging) expressions. If you know how to create formulas in Excel, you'll have no trouble creating expressions in VBA. With a worksheet formula, Excel displays the result in a cell. The result of a VBA expression, on the other hand, can be assigned to a variable or used as a property value.
VBA uses the equal sign (=) as its assignment operator. The following are examples of assignment statements (the expressions are to the right of the equal sign):
x = 1 x = x + 1 x = (y * 2) / (z * 2) FileOpen = True FileOpen = Not FileOpen Range("TheYear").Value = 2010
TIP
Expressions can be complex. You may want to use the line continuation sequence (space followed by an underscore) to make lengthy expressions easier to read.
Often, expressions use functions. These functions can be built-in VBA functions, Excel's worksheet functions, or custom functions that you develop in VBA. We discuss built-in VBA functions later in this chapter (see the upcoming section “Built-in Functions”).
Operators play a major role in VBA. Familiar operators describe mathematical operations, including addition (+), multiplication (*), division (/), subtraction (–), exponentiation (^), and string concatenation (&). Less familiar operators are the backslash (\) operator (used in integer division) and the Mod operator (used in modulo arithmetic). The Mod operator returns the remainder of one number divided by another. For example, the following expression returns 2:
17 Mod 3
VBA also supports the same comparison operators used in Excel formulas: equal to (=), greater than (>), less than (<), greater than or equal to (>=), less than or equal to (<=), and not equal to (<>).
With one exception, the order of precedence for operators in VBA is exactly the same as in Excel (see Table 3.3). And, of course, you can use parentheses to change the default order of precedence.
TABLE 3.3 Operator Precedence
| Operator | Operation | Order of Precedence |
^
|
Exponentiation | 1 |
* and /
|
Multiplication and division | 2 |
+ and -
|
Addition and subtraction | 3 |
| & | Concatenation | 4 |
| =, <, >, <=, >=, <> | Comparison | 5 |
CAUTION
The negation operator (a minus sign) is handled differently in VBA. In Excel, the following formula returns 25:
=-5^2
In VBA, x equals –25 after this statement is executed.
x = -5 ^ 2
VBA performs the exponentiation operation first and then applies the negation operator. The following statement returns 25:
x = (-5) ^ 2
In the statement that follows, x is assigned the value 10 because the multiplication operator has a higher precedence than the addition operator:
x = 4 + 3 * 2
To avoid ambiguity, you may prefer to write the statement as follows:
x = 4 + (3 * 2)
In addition, VBA provides a full set of logical operators, shown in Table 3.4. For complete details on these operators (including examples), use the VBA Help system.
TABLE 3.4 VBA Logical Operators
| Operator | What It Does |
Not
|
Performs a logical negation on an expression |
And
|
Performs a logical conjunction on two expressions |
Or
|
Performs a logical disjunction on two expressions |
Xor
|
Performs a logical exclusion on two expressions |
Eqv
|
Performs a logical equivalence on two expressions |
Imp
|
Performs a logical implication on two expressions |
The following instruction uses the Not operator to toggle the gridline display in the active window. The DisplayGridlines property takes a value of either True or False. Therefore, using the Not operator changes False to True and True to False.
ActiveWindow.DisplayGridlines = Not ActiveWindow.DisplayGridlines
The following expression performs a logical And operation. The MsgBox statement displays True only when Sheet1 is the active sheet and the active cell is in Row 1. If either or both of these conditions aren't true, the MsgBox statement displays False.
MsgBox ActiveSheet.Name = "Sheet1" And ActiveCell.Row = 1
The following expression performs a logical Or operation. The MsgBox statement displays True when either Sheet1 or Sheet2 is the active sheet.
MsgBox ActiveSheet.Name = "Sheet1" Or ActiveSheet.Name