Iteration (CIE IGCSE Computer Science)

What is iteration?

Iteration is the process of repeating a set of instructions until a specific condition is met. It is an important programming concept and is used to automate repetitive tasks.

There are three main types of iteration:

• Count-controlled loops
• Precondition loops
• Postcondition loops

• A count-controlled loop is used when the number of iterations is known beforehand
• It is also known as a definite loop
• It uses a counter variable that is incremented or decremented after each iteration
• The loop continues until the counter reaches a specific value

Example in Pseudocode:

count ← 1

FOR i <= 10

OUTPUT count

NEXT i

Example in Python:

for count in range(1, 11):

print(count)

Example in Java:

for(int count=1; count<=10; count++){

System.out.println(count);

}

Example in Visual Basic:

For count = 1 To 10

Console.WriteLine(count)

Next count

• A precondition loop is used when the number of iterations is not known beforehand and is dependent on a condition being true
• It is also known as an indefinite loop
• The loop will continue to execute while the condition is true and will stop once the condition becomes false

Example in Pseudocode:

INPUT temperature

WHILE temperature > 37 DO

OUTPUT "Patient has a fever"

INPUT temperature

END WHILE

Example in Python:

temperature = float(input("Enter temperature: "))

while temperature > 37:

print("Patient has a fever")

temperature = float(input("Enter temperature: "))

Example in Java:

Scanner input = new Scanner(System.in);

float temperature = input.nextFloat();

while (temperature > 37) {

System.out.println("Patient has a fever");

temperature = input.nextFloat();

}

Example in Visual Basic:

temperature = InputBox("Enter temperature")

Do While temperature > 37

Console.WriteLine( "Patient has a fever")

Console.WriteLine("Enter temperature")

temperature=Console.ReadLine()

Loop

• A post-condition loop is used when the loop must execute at least once, even if the condition is false from the start
• The condition is checked at the end of the loop
  
  

Example in Pseudocode:

REPEAT

INPUT guess

UNTIL guess = 42

Example in Python:

Postcondition loops don’t exist in Python and would need to be restructured to a precondition loop

Example in Java:

Scanner input = new Scanner(System.in);

int guess = 0;

do {

System.out.print("Enter guess: ");

guess = input.nextInt();

} while (guess != 42);

Example in Visual Basic:

Do

Console.WriteLine("Enter guess")

guess = Console.ReadLine()

Loop Until guess = 42