3. Software Design and Development

• Pre-defined functions

  • Length - returns number of characters
• Pre-defined function - Round

  • Rounds decimal number to specified number of decimal place


  Example:

  x = 12.12836

  print(round(x, 2))

  Output: 12.13
• Pre-defined function - Random

  • Generates random number


  Example:

  import random

  print(random.randint(1, 6))

  Output: 3
• Pre-defined function - Length

  • Returns number of characters 


  Example:

  x = "Blackpink"

  print(len(x))

  Output: 9
• Running Total with Loop

  > total = 0

  -

  > items = int(input("Enter number of items"))

  -

  > for counter in range(items):

  >> value = int(input("Enter value " + str(counter+1)+": "))

  >> total = total + value

  > print("The total is ", total)
• Input Vaildation

  > number = int(input("Enter a number between 1 and 10"))

  > while number < 0 or number > 10:

  >> print("Error: Invalid number")

  >> number = int(input("Re-enter number again: "))

  > print("Number is ", number)
• Selection Statements

  • AND - when both conditions are true
  • OR - when one condition is true
  • NOT - when condition is not true
• Types of Test Data

  • Normal test data - within the boundaries of the program


  Example: user's number needs to be between 1 and 5

  Test data would be: 1, 2, 3, 4, 5
• Types of Test Data

  • Extreme test data - the boundaries of the program


  Example: user's number needs to be between 1 and 5

  Test data would be: 1 and 5
• Types of Test Data

  • Exceptional test data - anything outside the boundaries of the program


  Example: user's number needs to be between 1 and 5

  Test data would be: -2, 0, "one"
• Types of Errors

  • Syntax error - a line of code not formed properly, caused by the programmer


  Example: "pirnt", instead of "print"
• Types of Errors

  • Execution error - occurs while the program is running, which the programs stops 


  Examples:

  • attempting to divide by 0,
  • attempting to assign one data type to a variable of a different data type, e.g. str value to int variable
• Types of Errors

  • Logic error - Does not produce the expected output 


  Examples:

  • using the wrong formula in a calculation,
  • entering infinite loop,
  • outputs not matching the labels, e.g. "Age: Jim"
• Evaluation - Fitness for purpose

  • If it meets all the functional requirements, then it's fit for purpose
  • If it fails to meet at least one functional requirement, then it's not fit for purpose
• Evaluation - Efficiency of code

  • Repetition - loops to repeat the same task
  • Arrays - instead of variables
  • Selection statements - else if, and else to select which code to run
  • Logical operators - AND, OR to reduce complexity of selection statements
• Evaluation - Robustness

  • If it doesn't crash when entering exceptional data, then the program is considered robust
• Evaluation - Readability

  • Making your program easy for you, and other programmers to understand your code, by using:
  • Internal comments;
  • Meaningful variables;
  • Indentation;
  • Whitespace
• Evaluation - Readability: Internal commentary

  • Comments that you leave to yourself, or other programmers to explain your code


  Example: ## this is an internal comment
• Evaluation - Readability: Meaningful variables

  • Using variables that help you understand your program
• Evaluation - Readability: Indentation

  • Makes it clear what loops, or if statements code belongs to
• Evaluation - Readability: Whitespace

  • Blank lines between lines of code, making it easier to see what belongs together