CS 1400

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CS 1400

• Course Reader
• Introduction

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What is Programming?

• Designing an appropriate algorithm
• Coding that algorithm in a computer language

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What is an algorithm?

• Def An algorithm is a logical sequence of
  instructions to accomplish a task.
• important points
• instructions must be well ordered
• instructions must be unambiguous
• the process must eventually end
• the actions must be doable
• the algorithm must produce the required result

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from a shampoo bottle

• lather
• rinse
• repeat
• algorithm critique
• too ambiguous
• doesnt end

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A more detailed algorithm for a shampoo bottle

• Wet hair
• Pick up shampoo bottle
• Open the bottle
• Pour some shampoo on your hand
• Close the shampoo bottle
• Set bottle down
• Put shampoo on hair
• Rub shampoo through hair until lather covers hair
  
• Rinse hair until all lather is removed
• Repeat the previous eight steps one more time

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What is a computer program?

• A computer program is just an algorithm expressed
  in computer language instructions

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Program development

• Steps
• analyze the problem
• outline the solution
• develop an algorithm in pseudocode
• test the algorithm
• code the algorithm into a computer language
• run and test the computer program
• document and maintain the program

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Computers are not smart!

• While instructions to a friend may assume implied
  understanding and intelligence, instructions to a
  computer need to be simple, specific, and
  detailed.
• The computer will not attempt to determine the
  purpose of your instructions it will only
  blindly carry them out.

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Types of user interfaces

• Graphical
• Console

next semester!
this semester
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Pseudocode

• flexible (no rigid syntax rules)
• English-like, but unambiguous
• contains
• keywords (words that have special meaning)
• variables (representations of a saved value)
• operators
• punctuation

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Keywords

• Get Else
• Print End If
• And Repeat
• Or End Repeat
• If While
• End While

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Operators

• (addition)
• - (subtraction)
• (multiplication)
• / (division)
• (assignment)

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A. Basic Calculations

• form ltvariablegt ltmath expressiongt
• Examples
• cost tax price
• (calculate the sum of tax and price, save the
  result as cost)
• area length width
• (calculate the product of length and width, save
  the result as area)

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B. Displaying messages and values

• form Print ltmessagegt
• form Print ltvariablegt
• Examples
• Print Hello!
• (display the message Hello on the screen)
• Print cost
• (display the current value of variable cost on
  the screen)

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C. Getting input

• form Get ltvariablegt from user
• Examples
• Get price from user
• (get the value for variable price from the users
  keyboard)

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Pseudocode Example 1

• Write a program to calculate the volume of a
  box, using dimensions provided by the user.
• Print Enter height, width, and depth of box
• Get height from user
• Get width from user
• Get depth from user
• volume height width depth
• Print Volume is
• Print volume

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Pseudocode Example 2

• Write a program to calculate a paycheck using
  regular hours, payrate, and overtime hours
  provided by the user. Assume overtime is paid at
  double.
• .

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D. Conditions

• form If ltcomparisongt
• ltstatements executed if truegt
• Else
• ltstatements executed if falsegt
• End If
• comparisons use
• lt, gt, lt, gt, !, , And, Or

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Example

• If age lt 21
• Print Sorry, you are too young
• Print Please try again next year
• Else
• Print You may enter
• End If

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D. Conditions (alternate)

• form If ltcomparisongt
• ltstatements executed if truegt
• End If
• Example
• If weight lt 90
• Print Consider eating more protein
• End If

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Example

• Write a program that gets an employee's
  information from a user and calculates their pay
  for the week. The input includes the employee
  total hours worked this week and their hourly
  wage. The employee is to be paid their basic wage
  for the first 40 hours worked and time-and-a-half
  for all hours above 40. Output the regular pay,
  overtime pay, and total pay for the week to the
  screen. If the employee worked 40 hours or less,
  do not output any information about overtime pay.

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Step 1 Analyze the problem

• Inputs
• hours worked, pay rate
• Given values
• over 40 hours is overtime
• overtime is 1.5 of regular pay
• Calculations
• regular pay, overtime pay, total pay
• Outputs
• regular pay, overtime pay (if present), total pay

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Step 2 Outline solution

• Get hours worked, and pay rate from a user
• If there was overtime, calculate regular pay on
  the first 40 hours and 1½ pay for additional
  hours
• Otherwise, calculate all hours worked at regular
  pay
• Print regular pay,
• If there was overtime, print the overtime pay
• Print total pay

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Step 3 Algorithm in Pseudocode

1. Print Enter hours worked
2. Get hours from user
3. Print Enter rate of pay
4. Get payRate from user
5. If hours gt 40
6. regularPay 40 payRate
7. overtimePay (hours 40) payRate 1.5
8. Else
9. regularPay hours payRate
10. overtimePay 0
11. End If
12. totalPay regularPay overtimePay
13. Print "Regular Pay ", regularPay
14. If overtimePay ! 0
15. Print "Overtime Pay ", overtimePay
16. End If
17. Print "Total for this week ", totalPay

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Step 4 Test algorithm
Instr screen name hours payRate regularPay overtimePay








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E. Repetition

• form Repeat ltNgt times
• ltstatements to be repeatedgt
• End Repeat
• Example
• Repeat 5 times
• Print Vote for Napoleon!
• End Repeat

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E. Repetition (alternate)

• form While ltcomparisongt
• ltstatements to be repeated if truegt
• End While
• Example
• Print Enter a positive number
• Get number from user
• While number lt 0
• Print Sorry, too low. Try again
• Get number from user
• End While

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Examples

• Write a program to output the squares of the
  numbers 1 through 100
• Write a program to output the sum of 50 product
  costs entered by the user
• Write a program to output the sum of a list of
  positive numbers entered by the user