Computer Programming Concepts and Visual Basic David I. Schneider

66 Computer Programming Concepts and Visual Basic
of the string or n is 0, then the empty string is returned. If m + n is greater than
the length of the string, then Mid(str, m, n) is the right part of the string beginning
with the mth character. The same is true for Mid(str, m). For instance, the
values of Mid(“abcdef ”, 3, 9) and Mid(“abcdef ”, 3) are both “cdef ”.
10. With FormatCurrency(n, r), fractional values are preceded by a leading zero,
and negative values are surrounded by parentheses instead of beginning with a
minus sign. The function has additional optional parameters. FormatCurrency(exp,
, vbFalse) suppresses leading zeros for fractional values. FormatCurrency(exp,
, , vbFalse) uses minus signs for negative numbers. For instance, the
value of FormatCurrency(–3/4, 3, vbFalse, vbFalse) is –$.750.
11. With FormatNumber(n, r), fractional values are preceded by a leading zero. The
function has additional optional parameters. FormatNumber(exp, , vbFalse)
suppresses leading zeros for fractional values. For instance, the value of FormatNumber(3/4,
3) is 0.750 and the value of FormatNumber(3/4, 3, vbFalse) is
.750. FormatNumber(exp, , , , vbFalse) suppresses commas.
12. When n is a number that is halfway between two whole numbers (such as 1.5,
2.5, 3.5, and 4.5), then n is rounded by Round(n) to the nearest even number.
That is, half the time n is rounded up and half the time is rounded down. For
instance, Round(2.5) is 2 and Round(3.5) is 4. Similar results hold for any number
whose decimal part ends in 5. For instance, Round(3.65, 1) is 3.6 and
Round(3.75, 1) is 3.8. On the other hand, FormatNumber, FormatCurrency, and
FormatPercent always round 5’s up. For instance, FormatNumber(2.5) is “3.00”.
13. The value of FormatDateTime(Now, vbLongDate) is today’s date. For any
positive number n, FormatDateTime(Now + n, vbLongDate) is the date n
days from today and FormatDateTime(Now - n, vbLongDate) is the date
n days ago.
14. The functions FormatNumber, FormatCurrency, FormatPercent, and
FormatDateTime were added to Visual Basic in VB6.0. The same results can be
obtained with the Format function alone. However, these new functions execute
faster than Format and are easier to use. In addition, they can be placed in
VBScript programs that are used to make Web pages interactive.
15. Each time the function Rnd appears in a program, it will be reassigned a value.
For instance, the task attempted (but not accomplished) by the first set of lines
that follows is achieved by the second set of lines. Because each of the Rnd’s in
the first set of lines will assume a different value, it is highly unlikely that the
square of the first one will equal the product of the last two.
‘Generate the square of a randomly chosen number
Randomize
picBox.Print “The square of”; Rnd; “is”; Rnd * Rnd’
Generate the square of a randomly chosen number
Randomize
numVar = Rnd
picBox.Print “The square of”; numVar; “is”; numVar * numVar
16. Additional information about the keywords, functions, methods, and properties
discussed in this section appear in Appendix C. With the Learning, Professional,
and Enterprise Editions of Visual Basic you can obtain a detailed (and somewhat
advanced) discussion about an item appearing in code by clicking on the
item and pressing F1. Other ways of obtaining help with these editions are presented
in Appendix B.