1. Basics of Computer Programming
Web Design
Section 8-1

2. Computer Programs
A computer program is nothing more than a set of instructions that tells the computer what to do
A computer program is also a way to tell another human being what you want the computer to do
Part of writing a computer program is to include documentation
Comments in the code, written document, etc.
Helps another human being understand what you are trying to do

3. Building Blocks of a Program
All computer programs are made from simple ideas…
A List of Instructions
Example:
Beat eggs
Mix in flour, sugar and shortening
Pour into a pan
Bake at 375 degrees for 45 minutes
This is called sequential processing

4. Building Blocks of a Program
Ifs
If something is true do this, otherwise do that…
Example – If it is raining take an umbrella
This is called Conditional Processing
Repeating Behavior
Examples:
Stomp your foot five times
While there are cookies on the plate, keep eating cookies
This is called Looping or Iteration

5. Building Blocks of a Program
Breaking Things Into Smaller Pieces
Example:
To clean the house we will first clean the kitchen, then clean the bathroom, and then clean the bedrooms one at a time.
This is called problem decomposition, stepwise refinement or top-down design
It’s really just breaking a complicated task down into a list of simpler tasks and then doing all those simple tasks.

6. Building Blocks of a Program
Compute a Result
Performing a sequence of tasks to obtain a result that is the answer to a question
Examples:
Look in the phone book and find the number for Rebecca Smith (Question really is “What is Rebecca Smith’s phone number?)
Put this baby on the scale and tell me how many pounds she weighs. (How much does the baby weigh?)
The question is known as a function and asking the question to get a result is known as calling a function

7. Computer Programming
Computer programming is just using those ideas in various combinations.
Computers really only understand about 100 different instructions!
The millions of programs that are out there are simply different combinations of those 100 instructions.

8. Designing a Program
The best way to design a program or for someone else or to see the logical flow of your own program is by sketching the design on paper.
One way of doing this is a visual representation called a Flowchart

9. Flowcharts Flowcharts are constructed using a set of basic symbols:
Processing
Terminal
Input/
Output
Call
Decision

10. Flowcharting Along with the symbols certain connectors are needed:
On Page
Connector
Off Page
Connector

11. Flowcharting Example This is a simple flowchart with no connectors
Start
Read a
value
Multiply the
value by 2 and
store in X
Display the
value entered
and X
Stop
This is a simple flowchart with no connectors
To follow the logic of a flow chart you start at the top and read downward.
What does this program do?

12. The Three Programming Control Structures.
All programs can be described by combining these 3 control structures:
Simple Sequence
Simple Selection
(IF-THEN-ELSE)
Simple Repitition
(Loop)
Funnily enough it was a couple of Italian computer scientists that came up with this idea to get over the spagetti problem. They said that all programs can be broken down into the 3 structures shown here. You can either design a program with one structure after the other after the other, or even insert one of the structure inside one of the other structures ( top-down design).

13. Flowcharting This is a simple flowchart for taking a bath.
Each of these processes can then be broken down into the steps associated with that process
Note the Start and End!
What is this program missing?

14. Flowcharting
This is the flowchart for the process “Fill the bathtub with water”
This process has decisions and loops!
Note that lines coming out of a decision are labeled with the answer

16. Friendship Algorithm

17. Summary
A computer program is simply a set of instructions which the computer must follow to solve a problem.
Computer programs are based on 5 simple ideas:
Sequential processing (a list of instructions)
Conditional Processing (Ifs)
Looping or Iteration (repeating)
Problem decomposition (Breaking Things Into Smaller Pieces)
Calling a function (Compute a Result)

18. Your Turn… Download 8-1 from the Hancock Web Site
On the first page on the homework the arrows are in the correct places. Simply move the boxes and the text to complete the flowcharts.
For the second page you can use Word or draw the flowchart by hand.
When done print out the homework and turn it in.