Chapter 1 – Intro to Computing
1.1 Types of Languages and Why They Are Useful
Computers require a method of instruction to operate. Modern computers get their instructions
from programming languages.
A programming language is an agreed-upon format of symbols that enables a programmer to
instruct a computer to perform certain predefined tasks.
There are two types of languages depending on how understandable they are: high- and lowlevel languages.
The Visual Basic Coach - 2002
Chapter 1 – Intro to Computing
The Development of Programming Languages
Manual switches using binary numbers
Assembly language and punch cards – two early breakthroughs
COBOL and FORTRAN – allowed programs to be run on another system than the original
PL/1 – result of one of the quests for a single universal language for all needs
C – originally used for developing operating systems, but became very popular
C++ and other object-oriented languages – enabled creation of reusable programs
Java – like C++, but can be run on any computer without recompiling
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Chapter 1 – Intro to Computing
1.2 Where Does Visual Basic .NET Fit In?
Visual Basic .NET has its roots in a language called BASIC which was
− Developed in 1964 to help nonscientists develop computer programs
− Quite limited in functionality
− Difficult to use for large, integrated systems
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Chapter 1 – Intro to Computing
Features of Visual Basic .NET
Visual Basic .NET is quite different from the original BASIC
− Complete development enivronment
−Primarily meant for developing prototypes and front ends for database applications.
− Truly object-oriented
− Part of the larger world of the .NET framework, which provides the same development
environment and contains the same object model. It is fairly easy to switch between different
languages within the framework. Objects developed in any of the .NET languages can be
accessed in the others.
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Chapter 1 – Intro to Computing
1.3 What Makes a Quality Program?
A quality program should have all of the following characteristics:
− Readability
− Modularity
− Efficiency
− Robustness
− Usability
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Chapter 1 – Intro to Computing
Readability
It is imperative that the program be written so that other programmers as well as the original
programmer can understand it since the maintenance phase of a computer project can actually
be more expensive than the original development process.
A key method a programmer can employ is to add comments to the program which explain the
program’s purpose and any unclear pieces of code.
It is also often necessary to produce external documentation.
A programmer who can produce readable, reliable code is valuable to a company and is less
likely to get stuck with maintaining cryptic code.
Programming standards/conventions are very important, especially when a group of
programmers work together.
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Chapter 1 – Intro to Computing
Modularity
Programs should be written in an orderly fashion with problems divided into smaller
subproblems and then assembled in a logical order.
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Chapter 1 – Intro to Computing
Efficiency
Visual Basic .NET is not usually used when high performance is the key design criteria.
Program size of the program itself is usually not an issue due to declining computer memory
prices and the large size of the .NET framework itself.
If you are improving efficiency of your VB .NET application, you are most likely adding
complexity without adding value to the application.
If you do decide to add cryptic lines for the purposes of speed and/or size, make sure to
document them and include a simpler way for others to easier understand your code.
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Chapter 1 – Intro to Computing
Robustness
A program should gracefully handle cases when the input to it is not as expected or some other
error has occurred. A program should never crash.
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Chapter 1 – Intro to Computing
Usability
A program must meet the needs of the end user, i.e. be correct, in order to be useful.
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Chapter 1 – Intro to Computing
1.4 Understanding Algorithms
An algorithm is a detailed sequence of steps required to solve a problem.
Algorithms can be represented in a graphical format called a flowchart. Flowcharts can be
large, but they are often useful.
Used to represent calculations and data manipulation.
Used to represent a comparison with either a
Yes/True result or a No/False result.
Used to represent the input or output of data.
Used to indicate the beginning or ending of a task.
These connector lines are used to join the other symbols within
the flowchart. The second and third ones are used in
conjunction with a Decision Box.
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Chapter 1 – Intro to Computing
An Example Algorithm
Step 1: Turn the stereo on.
Step 2: If the band is set to FM, switch it to AM.
Step 3: If the station is set to a station greater than 610, turn the station to the left until 610 is
reached.
Step 4: If the station is set to a station less than 610, turn the station to the right until 610 is
reached.
Step 5: Listen to the best sports talk station in the country.
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Chapter 1 – Intro to Computing
The flowchart of the example algorithm:
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Chapter 1 – Intro to Computing
1.5 Top-Down Versus Even-Driven Algorithms
Top-down or sequential problems are solved by traditional programming languages.
They lend themselves to problems that have a starting point, a predetermined series of steps,
and an ending point.
Algorithms that respond to external stimuli like clicking a mouse or selecting an item from a pulldown menu are considered event-driven.
The Visual Basic Coach - 2002
Chapter 1 – Intro to Computing
Consider the steps required to boil an
egg.
Step 1:
Open closet door.
Step 14:
Close the egg carton.
Step 2:
Remove pot.
Step 3:
Close closet door.
Step 15: Place the egg carton back in
the refrigerator.
Step 4:
Place pot under sink faucet.
Step 5:
Turn on the cold water.
Step 6:
Wait until the pot is ¾ full.
Step 7:
Turn off the cold water.
Step 8:
Place pot on stove burner.
Step 9:
Turn burner on high heat.
Step 10:
Open refrigerator door.
Step 11:
Take out the egg carton.
Step 22: Wait three minutes until the
egg is cooked.
Step 12:
Open the egg carton.
Step 23:
Shut off the stove burner.
Step 13:
carton.
Remove an egg from the
Step 24:
Remove the egg from the pot.
Step 16:
Close refrigerator door.
Step 17:
Open the silverware drawer.
Step 18:
Remove a large spoon.
Step 19:
Close the silverware drawer.
Step 20:
Wait until the water is boiling.
Step 21: When the water is boiling, use
the spoon to place the egg in the pot.
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Chapter 1 – Intro to Computing
Event-Driven Algorithms
Consider the steps required for playing tennis (for simplicity’s sake, let’s assume that you are
the one serving).
Step 1:
Walk up to the serving line.
Step 2:
Toss ball up in the air.
Step 3:
Swing the racket so that you hit the ball to the other player in the opposite box.
Step 4:
Wait for the ball to strike the tennis court.
Step 5A: If the ball lands legally in the box, wait to see if the opponent hits your serve back
toward you.
Step 5B: If the ball lands outside the box, you must serve again. Go to Step 1.
Step 6A: If the ball is hit back and it is hit to your right, move toward the right so you are in
position to hit it back.
Step 6B: If the ball is hit back and it is hit to your left, move toward the left so you are in
position to hit it back.
Step 6C:
If the ball is hit back and it is hit directly at you, wait for it to arrive.
Step 7A:
If the ball is hit back and it is hit in front of you, move forward.
Step 7B:
If the ball is hit back and it is hit behind you, move backward.
Step 8A: If the ball is hit outside the lines, do not hit it but let it pass. Serve again by going
to Step 1.
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Chapter 1 – Intro to Computing
1.6 Concept of an Object
Drill 1.4: Describe in detail the properties of a simple household phone and the actions that can
be performed upon it.
Properties:
1.
Button with the number 1 on it.
2.
Button with the number 2 and the letters ABC on it.
3.
Button with the number 3 and the letters DEF on it.
4.
Button with the number 4 and the letters GHI on it.
5.
Button with the number 5 and the letters JKL on it.
6.
Button with the number 6 and the letters MNO on it.
7.
Button with the number 7 and the letters PQRS on it.
8.
Button with the number 8 and the letters TUV on it.
9.
Button with the number 9 and the letters WXYZ on it.
10.
Button with the number 0 on it.
11.
Button with an * on it.
12.
Button with a # on it.
13.
Button with the word REDIAL on it.
14.
Large button with no wording on it.
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Chapter 1 – Intro to Computing
1.6 Concept of an Object
Describe in detail the properties of a simple household phone and the actions that can be
performed upon it.
Behaviors:
Button 1: If pushed, it enters the 1 digit of a phone number.
Button 2: If pushed, it enters the 2 digit of a phone number.
Button 3: If pushed, it enters the 3 digit of a phone number.
Button 4: If pushed, it enters the 4 digit of a phone number.
Button 5: If pushed, it enters the 5 digit of a phone number.
Button 6: If pushed, it enters the 6 digit of a phone number.
Button 7: If pushed, it enters the 7 digit of a phone number.
Button 8: If pushed, it enters the 8 digit of a phone number.
Button 9: If pushed, it enters the 9 digit of a phone number.
Button 0: If pushed, it enters the 0 digit of a phone number.
Button *: Used to interact with computer systems that the phone may connect to.
Button #: Used to interact with computer systems that the phone may connect to.
REDIAL Button: If pushed, it dials the last phone number entered into the phone.
Large Button: This hangs up the phone, which ends the phone call and resets the phone.
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Chapter 1 – Intro to Computing
1.6 Concept of an Object
Describe in detail the properties of a simple digital alarm clock and the actions that can be
performed upon it.
Properties:
1. Hour Display: An LCD output to display the hour of the time being displayed. It can be a
number from 1 to 12.
2. Minute Display: An LCD output to display the current minute of the time being displayed. It
can be a number from 0 to 59.
3. Second Display: An LCD output to display the current second of the time being displayed. It
can be a number from 0 to 59.
4. A.M./P.M. Display: An LCD output to display an indicator of whether the current time is in the
A.M. or P.M. for the time being displayed.
5. Current Hour: The hour of the current time. It can be a number from 1 to 12.
6. Current Minute: The minute of the current time. It can be a number from 0 to 59.
7. Current Second: The second of the current time. It can be a number from 0 to 59.
8. Current A.M./P.M.: An indicator of whether the current time is in the A.M. or P.M.
9. Alarm Hour: The hour of the time the alarm will go off if it is set to go off. It can be a number
from 1 to 12.
10. Alarm Minute: The minute of the time the alarm will go off if it is set to go off. It can be a
number from 0 to 59.
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Chapter 1 – Intro to Computing
1.6 Concept of an Object
Describe in detail the properties of a simple digital alarm clock and the actions that can be
performed upon it.
Properties (continued):
11. Alarm Second: The second of the time the alarm will go off if it is set to go off. It can be a
number from 0 to 59.
12. Alarm A.M./P.M.: An indicator of whether the alarm will go off in the A.M. or P.M., if the alarm
is set.
Behaviors:
1. Set Alarm: Set the hour, minute, and A.M./P.M. of the alarm.
2. Set Time: Set the hour, minute, and A.M./P.M. of the actual time.
3. Fast Button: If the switch is in either Set Alarm or Set Time position, increment the Alarm
Time or Actual Time at a fast pace. As long as the button is depressed, the time will continue to
increment.
4. Slow Button: If the switch is in either Set Alarm or Set Time position, increment the Alarm
Time or Actual Time at a slow pace. As long as the button is depressed, the time will continue to
increment.
5. Activate Alarm: If the button is pressed, the alarm is set to go off at the time indicated by the
Alarm Time.
The Visual Basic Coach - 2002
Chapter 1 – Intro to Computing
1.6 Concept of an Object
Describe in detail the properties of a simple digital alarm clock and the actions that can be
performed upon it.
Behaviors (continued):
6. Deactivate Alarm: If the button is pressed and the alarm is on, shut it off.
7. Increment Time: The clock will automatically increment the time by a second every second
and display it. If the new time is equal to the Alarm Time and the alarm is set to go on, then the
alarm will sound.
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Chapter 1 – Intro to Computing
1.7 Interpreters, Compilers, and JITs
High-level languages like Visual Basic .NET must be converted into a language the machine
understands before it can execute it. There are three main methods for accomplishing this task:
 Interpreting. An interpreter is a program that converts the language at the time the
application is executed. This leads to slow executing applications.
 Compiling. A compiler will perform all of the translation at once and store the results in a file
called an executable. This results in a faster execution but one which is compiled for a specific
computer chip.
 Just-in-time compiling (JIT). JIT compilers compile the source code into an intermediate
language which is then translated just in time to be executed by the computer. Visual Basic
.NET and Java use this method.
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