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Introduction to Algorithms

Introduction to Algorithms. Yonglei Tao. What is an Algorithm?. A step-by-step description about a solution to a problem Unambiguous In a logical order Executable A program is the expression of an algorithm in a programming language. Examples of Algorithm. Making a phone call

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Introduction to Algorithms

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  1. Introduction to Algorithms Yonglei Tao

  2. What is an Algorithm? • A step-by-step description about a solution to a problem • 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 • 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

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

  6. 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

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

  8. 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

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

  10. 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”

  11. 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 • avg = ( a + b + c ) / 3 • sum = a + b + c • Print sum, avg

  12. Example • Write pseudocodethat 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

  13. Exercise • Write pseudocodethat inputs the length and width of a carpet in feet and the price in dollar per square yard. The algorithm should print out the total cost of the carpet, including a 6% sales tax.

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