Excel and Visual Basic
Chapter I – The Visual Basic Language
Before we start
Computers store information in memory. The basic memory element is the byte (a set of
8 bits, each bit can have the value 0 or 1). With a byte you can have bits combination
from binary - 00000000 (decimal 0) to binary – 11111111 (decimal 255), 256
combinations in all (having 8 bits you have 2 8 = 256 combinations). In memory you can
only have numbers (in a byte you have a integer number from 0 to 255). So how can
you store information in memory if that information is not an integer number? The
answer is easy, you just store an integer number that represents (codes) that information.
If you want to save 256 different colors in a byte you just code the colors (0 – white, 1 –
black, 2 – yellow, 3 – red, …). You don’t store the color but just the number that
represents it. It’s the same with letters, computers don’t store the letter just a number
that represents it.
So in memory you have only numbers. Information is the way we interpret those
numbers.
1 – Fundamental Data types
A type is a class that represents information with the same characteristics. We group
information with common characteristics in classes. We give a name to each one of
those classes. In a programming language we store information in variables (well,
information is stored in computer memory so variables represent one or more bytes in
memory).
When we say : X is an integer variable - we mean X can store values with the
characteristics of the integer numbers.
Types have two fundamental characteristics:
- The set of values information can take
- Operations you can use with those values
1.1 The integer type
In VB an integer variable can store integer numbers (set of values) from –32768 to
32767
Where this number comes from?
Vb uses two bytes to store integer numbers. We have in all 16 bits so we can have
numbers from binary - 00000000 00000000 (decimal 0) to binary – 11111111
11111111 (decimal 65535 --»»216 -1). Integer number can be negative too, so we must
have a way to represent those numbers. Computers use one of the bits (the one at the
left) to say if the integer number is positive or negative. If that bit is 0 the number is
positive, if the bit is 1 the number is negative. So the biggest positive integer is 0111
1111 1111 1111 (first bit must be 0 to be positive). This is decimal 32767. If we add 1
to this number we will have binary – 1000 0000 0000 000 (decimal 32768). If we look
closer we see that first bit is 1 so this must be a negative number. It is the negative
number –32768.
Valid operations: (operations between integers that also return an integer value)
+ addition
- subtraction
* multiplication
\ integer division
Expression 7 \ 3 results 2
MOD remainder after integer division
Expression 7 MOD 3 results 1
^ power
Expression 2^3 results 8
You can also use normal division (/) between integers but result is no longer an
integer but a floating-point value.
Expression 4 / 2 results 2.0
Some VB functions that return integer values
Function Sintax
Returns
Expression example
Returns
Int(number)
Integer part of number *
Fi x(number)
Integer part of number *
Round(expression
[,numdecimalplaces])
A number rounded to a
specified number of decimal
places
A number rep resented by
string
A number converted fro m
string or expression
Int(8.7)
Int(-8.7)
Fi x(8.7)
Fi x(-8.7)
Round(17.267)
Round(17.6)
Round(17.267, 2)
Val(“123”)
8
-9
8
-8
17
18
17.27
123
Cint(17.6)
Cint(“17.6”)
Asc(“A”)
18
176
65
Asc(“Apple”)
65
Abs(-5)
5
Val(string)
Cint (string or
numeric expression )
Asc(string)
Abs(number)
Integer representing the
char code of the first letter o f
string
Absolute value of number
*The difference between Int and Fix is that if number is negative, Int returns the first negative integer less than or equal
to number, whereas Fix returns the first negative integer greater than or equal to number.
1.2 The long type
Longs are just big integers.
VB uses 4 bytes to store long numbers. We can now represent values from –
2147483648 to 2147483647.
Everything else said for integer type is valid for longs, the only exception is the Cint
function replaced by the Clng function.
1.3 The single type
We can use singles to store single-precision floating-point numbers. Singles range in
value from -3.402823E38 to -1.401298E-45 for negative values and from 1.401298E-45
to 3.402823E38 for positive values. (3.402823E38 means 3.402823 x 10 38 )
Single-precision numbers can have up to 7 digits precision mantissa (part to the left of
the E in a floating-point number)
Valid operations:
+ addition
- subtraction
* multiplication
/ division
^ power
1.4 The double type
We can use doubles to store double-precision floating-point numbers. Doubles range in
value from -1.79769313486231E308 to -4.94065645841247E-324 for negative values
and from 4.94065645841247E-324 to 1.79769313486232E308 for positive values.
Double-precision numbers can have up to 15 digits precision mantissa (the part to the
left of the E in a floating-point number)
Valid operations:
The same as the single type
Some VB functions that return single or double values
Function Sintax
Returns
Expression example
Returns
Cos(angle)
a Double specify ing the
cosine of angle*
a Double specify ing the sine
of angle*
a Double specify ing the
tangent of angle*
a Double specify ing the
natural logarith m of number
(base e logarith m)
a Double specify ing the
square root of a number
a single random value less
than 1 but greater than or
equal to zero
A number rep resented by
string
Absolute value of number
Cos(0)
1.0
Sin(0)
0.0
Tan(0)
0.0
Log(1)
0.0
Sqr(4)
2.0
Int(1 +10*rnd)
Val(“123.17”)
Integer
between 1
and 10
123.17
Abs(-5.0)
5.0
Sin(angle)
Tan(angle)
Log(number)
Sqr(number)
Rnd()
Val(string)
Abs(number)
* angle is expressed in radians
1.5 The Boolean type
A variable of type Boolean can only take the values true or false.
Valid operations:
AND logical conjunction
OR logical disjunction
NOT logical negation
XOR logical exclusion
Ope ration results
True AND True
True AND False
False AND True
False AND False
True
False
False
False
True OR True
True OR False
False OR True
False OR False
True
True
True
False
True XOR True
True XOR False
False XOR True
False XOR False
False
True
True
False
NOT True
NOT False
False
True
Examples :
(5>2) AND (3=2)
(5>2) OR (3=2)
(5>2) XOR (3=2)
NOT (5>2)
results
results
results
results
False
True
True
False
Note : The AND, OR and XOR operators also perform a bitwise comparison of
identically positioned bits in two numeric expressions and sets the corresponding bit in
result according to the following table:
Bit in expression1
Bit in expression2 AND
OR
XOR
Corres ponding bi t in result
1
1
0
0
1
0
1
0
1
0
0
0
1
1
1
0
0
1
1
0
For example 5 AND 3 results 1 ----» 101 AND 011 = 001 (in binary)
The Not operator inverts the bit values of any nume ric expression and sets the
corresponding bit in result accordingly.
Some VB functions that return boolean values
Functi on Sintax
EOF(filenumber)
Returns
Expression example
True when the end of a file opened for
Random or sequential Input has been
reached, False otherwise
Is Empty(expression)
True if the variable is uninitialized, or
is explicitly set to empty; otherwise, it
returns False . False is always returned
if expression contains more than one
variable. IsEmpty only returns
meaningful information for variants
True if expression is Null; otherwise,
IsNull returns False.The Null value
indicates that the Variant contains no
valid data.
Dim InputData
Open "MYFILE" For Input As #1 'Open file for input
Do While Not EOF(1) 'Check for end of file
Line Input #1, InputData 'Read line of data.
Debug.Print InputData 'Print to the Immediate windo w.
Loop
Close #1
' Close file.
Dim MyVar, MyCheck
MyCheck = IsEmpty(MyVar)
IsNull(expression)
Is Error(expression)
Boolean value indicating whether an
expression is an error value
IsNumeric(expression)
True if the entire expression is
recognized as a number; otherwise, it
returns False
True if the expression is a date or is
recognizable as a valid date; otherwise,
it returns False
IsDate(expression)
Returns
cells(1,1).=”Hello World”
TRUE
FALS E
cells(1,1).ClearContents
TRUE
Dim MyVar, MyCheck
MyCheck = IsNull(MyVar)
My Var =””
MyCheck = IsNull(MyVar)
My Var =null
MyCheck = IsNull(MyVar)
IsDate(“8-10-2006”)
FALS E
FALS E
TRUE
TRUE
FALS E
FALS E
TRUE
TRUE
IsDate(“32-12-2006”)
FALS E
MyCheck = IsEmpty(cells(1,1))
MyCheck = IsEmpty(cells(1,1))
IsError (evaluate(“5 / 0”))
IsError (evaluate(“5 / 2”))
IsNumeric(“Hello World”)
IsNumeric(“732”)
1.6 The string type
We can use strings to store one or more characters. Characters include uppercase and
lowercase letters, digits and symbols. All the characters are saved in memory using a
numeric (0 – 255) code, the ASCII code for that character. As there are 256 ASCII
codes, each string occupies a byte in memory for each character. The first 128
characters (0–127) of the character set correspond to the letters and symbols on a
standard U.S. keyboard. These first 128 characters are the same as those defined by the
ASCII character set. The second 128 characters (128–255) represent special characters,
such as letters in international alphabets, accents, currency symbols, and fractions.
Codes 0 to 31 are control codes such TAB, BACKSPACE, CARRIAGE RETURN.
We can have two kinds of strings in VB
- Fixed length strings
(Length cannot change during program execution)
A fixed-length string can contain 1 to approximately 64K (2^16) characters.
Declaration of a fixed 8 char length string
DIM sbyte as string*8
-
Variable length strings
(Length can change during program execution)
A variable-length string can contain up to approximately 2 billion (2^31) characters
Declaration of a variable length string
Dim name as string
Literal value strings are always placed within quotation marks “”
Example: name = “Shakespeare”
Valid operations:
& Concatenation
Expression “HI ” & “THERE” results “HI THERE”
Some Subprograms that work with STRINGS
Functi on Sintax
Returns
Expression example
Returns
Len(string)
a long containing the number of
characters in string
Len(“ Shakespeare”)
11
Lef t(string,lenght)
a string containing lenght number of
characters fro m the left side of string.
Lef t(“ Shakespeare”,5)
“Shake”
Right(string,lenght)
a string containing lenght number of
characters fro m the right side of string.
Right(“ Shakespeare”,5)
“peare”
Mid( string, start[, length])
a string containing length number of
characters fro m string starting at start.
If length is omitted all characters fro m
the start position to the end of string
are returned.
Mid(“ Shakespeare”,2,4)
“hake”
Mid(“ Shakespeare”,6)
“speare”
a long specifying the position of the
first occurrence of string2 within
string1. start is the starting position
for e ach search. I f o mitted, search
begins at the first character position. If
search fails function returns 0.
a long specifying the position of the
last occurrence of string2 within
string1. start is the starting position
for e ach search. I f o mitted, search
begins at the last character position. If
search fails function returns 0.
InStr(“ Shakespeare” ,”spe”)
6
InStr(“ Shakespeare” ,”rat”)
0
InStr(4,“ Shakespeare” ,”a”)
9
InStrRev(“ This is VBA”,”i”)
6
InStrRev(“ This is VBA”,”i”,4)
3
InStr([start, ]string1, string2)
InStrRev(string1, string2[,start])
[] Optional parameters