1. Introduction to Algorithms
Yonglei Tao

2. What is an Algorithm?
A step-by-step description about how to perform a task
Unambiguous
In a logical order
Executable
A program is the expression of an algorithm in a programming language

3. Examples of Algorithm Making a phone call Other examples
Pick up the receiver
Hear the dial-tone
Dial a phone number
Wait for the reply
Talk
Replace the receiver
Other examples
Programming a VCR
A recipe for a cake

4. Building Instructions for LEGO

6. Developing an Algorithm
How to develop an algorithm?
Problem solving
How to describe an algorithm?
In English?
In a programming language?

7. Pseudocode
English statements + basic control structures in programming languages
Good compromise
Simple, readable, no strict rules, don’t worry about punctuation
Let you think at an abstract level about the problem
Allow you to focus on what needs to be done without having to deal with the syntax and grammar of a programming language

8. Pseudocode vs. Code Pseudocode VB code Get the rate from user
dblRate = Convert.ToDouble(txtRate.Text)

9. Building Blocks for Pseudocode
Basic statements
Get the input (from user)
Print the output (on the screen)
Perform basic calculations
Conditional and iterative statements
Variables

10. Variables How to do (2 + 3) * (5 – 1) using a calculator?
A variable is a memory location
Can store a value
Addressable by its name
Examples
count 1
sum 5

11. Basic Statements
Assign values to variables using basic arithmetic operations
Set the value of x to 3 or x = 3
Set the value of y to x/10 or y = x/10
Set the value of z to x +25 or z = x + 25
Get input from user
Get the value of x
Print results to the screen
Print the value of y, z
Print “CIS160 Visual BASIC”

12. Example
Write pseudocode that asks the user for three numbers, computes their sum and average and outputs the results.
Get the values of a, b, c from user
sum = a + b + c
avg = sum / 3
Print sum, avg
Input
Process
Output

13. Example
Write pseudocode that reads the value of a circle radius from the user, and prints the area of a circle with that radius
Get the value of radius from user
area = pi * radius * radius
Print “The area of your circle is “ & area

14. Exercise
Write pseudocode that inputs the length and width of a carpet in feet and the price in dollar per square yard. It also prints out the total cost of the carpet, including a 6% sales tax.
1 square yard = 9 square feet