Computer Programming Concepts and Visual Basic David I. Schneider

to the file by the filespec “C:\DATA.TXT” produces the run-time error “File
not found.”
The dialog box generated by a run-time error states the type of error and has a
row of four command buttons captioned Continue, End, Debug, and Help. If
you click on the Debug command button, Visual Basic will highlight in yellow
the line of code that caused the error. (Note: After a run-time error occurs, the
program is said to be in break mode. See the first page of Appendix D for a discussion
of the three program modes.)
7. A third type of error is the so-called logical error. Such an error occurs when
a program does not perform the way it was intended. For instance, the line
ave = firstNum + secondNum / 2
is syntactically correct. However, the missing parentheses in the first line are
responsible for an incorrect value being generated. Appendix D discusses
debugging tools that can be used to detect and correct logical errors.
8. The omission of the asterisk to denote multiplication is a common error. For
instance, the expression a(b + c) is not valid. It should read a * (b + c).
9. The largest number that most of the numeric variables considered in this text
can represent is 3.402823E+38. Attempting to generate larger values produces
the message “Overflow.” The numbers generated by the programs in this text
usually have a maximum of seven digits.
10. A Review of Exponents. The expression 23 means 2 � 2 � 2, the product of three
2’s. The number 3 is called the exponent, and the number 2 is called the base.
In general, if r is a positive integer and a is a number, then a is defined as follows:
a r = a � a. . . a
r factors
The process of calculating a r is called raising a to the rth power. Some other
types of exponents are the following:
a 1 / 2 = �a� 9 1\2 = 3
a 1/n = n �a� n positive integer 16 1/4 = 2
a m/n = ( n �a�) m m, n positive integers 8 2/3 = ( 3 �8�) 2 = 4
a –r = 1/a r a ≠ 0 10– 2 = .01
11. More than one statement can be placed on a single line of a program provided
the statements are separated by colons. For instance, the code inside the event
procedure in Example 3 can be written as
picResults.Cls: a = 5: b = 4: picResults.Print a * (2 + b)
In general, though, programs are much easier to follow if just one statement
appears on each line. In this text, we almost always use single-statement lines.
12. When you first open a program that has been saved on disk, the Code window
may not appear. If so, run and then terminate the program to see the Code window.
To see the Form window, click on Object in the View menu or press
Shift+F7. To return to the Code window, click on Code in the View window or
press F7.
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