Iteration

• Iteration


  Repeating steps or instructions over and over again until a particular condition is met
• Iteration

  • Simplifies an algorithm
  • Is quicker
  • Does not include lots of unnecessary steps
• Condition


  A situation that is checked every time. If the condition is false the iteration repeats and if it is true the condition stops
• Counter


  They can keep count of how many iterations have been completed
• Iteration is the act of repeating a process until there is a desired outcome
• Real-world examples where humans iterate on a regular basis

  • Practising sports
  • Boiling water
  • Practising an instrument
• WHILE loop

  1. Index = 0

  2. WHILE index <= 10

  3. OUTPUT("The number is " + index)

  4. Index = index + 1
• Python WHILE loop

  1. Print("Please insert £8 for a ticket")

  2. While total < 8

  3. coins = int(input("Enter pound coins"))

  4. total = total + coins

  5. print("Amount entered", total)

  6. print("Thank you!")
• FOR loop

  • Pseudocode uses a variable name and has to show the start and end
  • Python uses a string and you only have to show the end but it doesn't go up to the end number
• WHILE loop

  • Pseudocode similar to FOR loop but you use < or .
  • Python once you do what is asked the loop is dropped and it proceeds with the code
• Definite iteration

  The number of iterations that are going to happen before the iteration of the loop
• WHILE loop algorithm

  1. number = int(input('Please enter your number.'))

  2. Index = 1

  3. While index < = 12:

  4. print(index + 'x' + number + '=' + number + index

  5. INDEX = INDEX + 1
• Python algorithm for entering low and high numbers

  1. a = int(input("Enter a low number: ")

  2. b = int(input("Enter a higher number: ")

  3. while a <= b

  4. print(a)

  5. a = a+1
• Indefinite iteration

  The number of iterations is not known before the loop is started
• Definite iteration

  The number of iterations is known before the execution of the loop is started
• Python algorithm for summing numbers


  1. sum = 0

  2. n = int(input("Enter numbers: ")

  3. q = input("Do you want to enter more numbers")

  4. While q != "No":

  5. sum = sum + n

  6. q = input("Do you want to enter a number")

  7. N = int(input("Please enter a number"))

  8. print(sum + n)
• WHILE loop

  The loop continues WHILE a certain condition remains true. The condition is checked before the code is executed
• REPEAT...UNTIL loop


  The comparison is not done UNTIL the end of the code block
• Python algorithm for summing numbers with option to enter more


  1. Total = 0

  2. n = int(input("Please enter a number: ")

  3. q = input("Do you want to enter more numbers? y/n")

  4. While q == "y"

  5. total = total + n

  6. N = int(input("Please enter a number: "))

  7. Q = input("Do you want to enter more numbers? ")

  8. Else:

  9. total = total + n

  10. print(total)
• Python algorithm for guessing game

  1. play = input("Do you want to play? Y?N" )

  2. While play == "Y":

  3. Import random

  4. N = random.randint(1,100)

  5. guess = 0

  6. While guess == 0

  7. guess = int(input("Enter a guess: ")

  8. elif guess > n:

  9. Guess = 0

  10. print("Your guess is too low.")

  11. Else:

  12. print("Well done. You guessed correctly!")

  13. play = input("Do you want to play again?")

  14. print("You have ended the game.")
• Nesting

  One loop can be run inside another loop
• Python algorithm for calculating tea and coffee sales

  1. for tea in range(101)

  2. For coffee in range (101)

  3. Total = tea*1.2 + coffee*1.9

  4. If total == 285:

  5. print("Number of tea cups sold", tea)

  6. print("Number of coffee cups sold", coffee)
• Three building blocks to use when designing algorithms

  • Sequencing
  • Selection
  • Iteration
• Iteration


  Repeating steps in an algorithm
• Selection


  A decision
• Python algorithm for times tables

  1. Num1 = int(input("Enter the first number."))

  2. Num2 = int(intput("Enter the second number"..))

  3. While num1 <= num2

  4. print(f"This is the (num1 times table.")

  5. For x in range(1,13):

  6. print(f"{x} x {num} = (x*num1")

  7. Num1 = num1 + 1
• Iteration is important as it allows us to simplify an algorithm by removing unnecessary steps
• Infinite loop


  These are also called endless loops because they go on repeating and never stop
• Condition


  A situation that is checked every time iteration occurs
• Infinite loops can be created intentionally to repeat a task indefinitely
• Placing a condition in a 'WHILE' loop that will always be true can create an infinite loop
• Testing a condition


  Checking to see if a condition has been met
• Iteration means that a procedure or a set of statements or commands is repeated a set number of times or until there is a desired outcome
• Iteration in pseudocode

  REPEAT-UNTIL
• Iteration in a flowchart

  Represented as a decision
• WHILE loop

  Runs until a condition becomes false
• Counter (in iteration)


  Used to keep track of how many times the solution has iterated
• REPEAT...UNTIL loop

  Runs until a condition becomes true
• WHILE loop

  Tested at the start of a loop
• REPEAT...UNTIL loop

  Tested at the end of a loop