iteration

Iteration

What is iteration?

• Iteration is the process of doing something more than once (repeat), otherwise known as a loop

• A loop can be count controlled which means the code is repeated a fixed number of times

• A loop can also be condition controlled which means the code is repeated until a condition is met

• Three common loops are:

  • for loops (count controlled)

  • while loops (condition controlled)

  • do while loops (condition controlled)

For Loops

• A for loop is a count controlled loop that will repeat a fixed number of times. It provides a concise and structured way to perform repetitive tasks.

Syntax of a for loop

The syntax of a for loop consists of three main parts:

01 for i = x to y
02 // Code to be executed in each iteration
03 next i

1. Initialisation: The initialisation is executed only once at the beginning of the loop. It is used to initialise a counter variable that controls the loop’s execution which is i in this example

2. Range: The range that the count variable will increment through

3. Increment/Decrement: The default is to increment by 1 each time unless specified

Pseudocode example

for loop example pseudocode

Python example

01 for i in range(0,6):
02 print i

In Python, the range specifies the numbers used in the loop. The final number (6 in this case) is 1 higher than the number we want to run the loop with.

Java example

01 for (int i = 0; i < 6; i++) {
02 System.out.println(i);
03 }

Iterating over an array

Pseudocode example

for loop iterating over an array and outputting each item

Python example

01 fruits = ["apple", "banana", "orange"]
02 for i in range(len(fruits)):
03 print(fruits[i])

Java example

01 String[] fruits = {"apple", "banana", "orange"};
02 for (int i = 0; i < fruits.length; i++) {
03 System.out.println(fruits[i]);
04 }

While Loops

• A while loop is a condition controlled loop that will repeat until a condition is met 

• While loops provide a flexible and powerful way to handle situations where the number of iterations is unknown in advance

Syntax of a while loop

• The syntax of a while loop consists of a condition and a code block:

01 while condition
02 // Code to be executed as long as the condition is true
03 endwhile

• The condition is evaluated before each iteration. If the condition evaluates to true, the code block is executed

• If the condition evaluates to false, the loop terminates.

Pseudocode example

while loop example pseudocode

Python example

01 i = 0
02 while i <= 5:
03 print(i)
04 i = i + 1

Java example

01 int i = 0;
02 while (i <= 5) {
03 System.out.println(i);
04 i = i + 1;
05 }

Checking if the password is ‘secret’

Pseudocode example

while loop checking if the password is correct

Python example

01 password = ""
02 while password != "secret":
03 password = input("What is the password? ")

Java example

01 import java.util.Scanner;
02 public class Main {
03 public static void main(String[] args) {
04 Scanner scanner = new Scanner(System.in);
05 String password = "";
06 while (!password.equals("secret")) {
07 System.out.print("What is the password? ");
08 password = scanner.nextLine();
09 }
10 scanner.close();
11 }
12 }

Do While Loops

• A do while loop is another example of a condition controlled loop that will repeat until a condition is met. 

• Do while loops provide a variation of the while loop with a slightly different behaviour

• The code within a do while loop will always run at least once, unlike a while loop which may not run at all if the condition is already met

Syntax of a do while loop

• The syntax of a do while loop consists of a code block and a condition:

01 do
02