Imagine you need to print "Hello" 100 times. Would you write 100 print() statements? Of course not! That's what for loops are for — they let you repeat code a specific number of times.

🔁 The Basic for Loop with range()

Syntax:

for variable in range(count):
    # code to repeat

Example — repeat 5 times:

for i in range(5):
    print("Hello!")

Output:

Hello!
Hello!
Hello!
Hello!
Hello!

Example — print the loop variable:

for i in range(5):
    print(f"Iteration {i}")

Output:

Iteration 0
Iteration 1
Iteration 2
Iteration 3
Iteration 4

🎯 Customising range(start, stop, step)

Syntax:

range(start, stop)     # from start to stop-1
range(start, stop, step)  # with custom step

Example — start at 1, stop before 6:

for i in range(1, 6):
    print(i, end=" ")   # 1 2 3 4 5

Example — count by 2s:

for i in range(2, 11, 2):
    print(i, end=" ")   # 2 4 6 8 10

Example — count down:

for i in range(10, 0, -1):
    print(i, end=" ")   # 10 9 8 ... 1

print("🚀 Blast off!")

📋 Looping Through a List

Syntax — for-each style:

for item in list:
    print(item)

Example:

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(f"I love {fruit}s!")

Output:

I love apples!
I love bananas!
I love cherries!

Using index — range(len()):

numbers = [10, 20, 30, 40]
for i in range(len(numbers)):
    print(f"Index {i}: {numbers[i]}")

🔢 enumerate() — Index and Value Together

students = ["Alice", "Bob", "Charlie"]
for i, name in enumerate(students):
    print(f"Student {i+1}: {name}")

Output:

Student 1: Alice
Student 2: Bob
Student 3: Charlie

🛑 break and continue

break — exit the loop immediately:

for i in range(10):
    if i == 5:
        break       # stop when i reaches 5
    print(i, end=" ")   # 0 1 2 3 4

continue — skip to the next iteration:

for i in range(10):
    if i % 2 == 0:
        continue    # skip even numbers
    print(i, end=" ")   # 1 3 5 7 9

🧮 Algorithms with For Loops — Totalling and Counting

Now that you understand the basic for loop, let's look at two essential exam patterns.

Totalling — add up values:

total = 0
for score in [45, 78, 92, 60, 55]:
    total = total + score   # or total += score
print(f"Total: {total}")    # 330

Counting — count how many match a condition:

count = 0
for score in [45, 78, 92, 60, 55]:
    if score >= 50:
        count = count + 1   # or count += 1
print(f"Passed: {count}")   # 4

Combined — find average:

scores = [45, 78, 92, 60, 55]
total = 0
count = 0

for s in scores:
    total += s
    count += 1

average = total / count
print(f"Average: {average:.1f}")  # 66.0

🔄 REPEAT...UNTIL (Post-condition Loop)

IGCSE pseudocode has a loop that always runs at least once. In Python, we use while True + break:

# Pseudocode equivalent:
# REPEAT
#     OUTPUT "Enter a positive number:"
#     INPUT num
# UNTIL num > 0

while True:
    num = int(input("Enter a positive number: "))
    if num > 0:
        break
    print("Try again!")

A while loop keeps running as long as a condition is True. Unlike for (which runs a fixed number of times), while is perfect when you don't know how many iterations you'll need.

🔄 The Basic while Loop

Syntax:

while condition:
    # code to repeat

Example — count to 5:

count = 0
while count < 5:
    print(f"Count is {count}")
    count = count + 1   # 🔑 Don't forget to update!

Output:

Count is 0
Count is 1
Count is 2
Count is 3
Count is 4

🧠 Using while with User Input

A very common use — keep asking until the user gives valid input.

num = 0
while num <= 0:
    num = int(input("Enter a positive number: "))
    if num <= 0:
        print("That's not positive! Try again.")

print(f"Thanks! You entered {num}")

🎯 while vs for — When to Use Which

🛑 Using break to Exit a While Loop

while True:
    cmd = input("Enter command ('quit' to exit): ")
    if cmd == "quit":
        break
    print(f"Executing: {cmd}")

while True creates an infinite loop — but break lets you exit from inside.

🧮 Algorithms with While Loops — Totalling with Unknown Count

Now that you understand the basic while loop, here's the key exam pattern:

# Enter scores until -1, then show average
total = 0
count = 0
score = int(input("Enter score (-1 to stop): "))

while score != -1:
    total += score
    count += 1
    score = int(input("Enter score (-1 to stop): "))

if count > 0:
    print(f"Total: {total}")
    print(f"Average: {total/count:.1f}")
else:
    print("No scores entered.")

Finding the first match:

# Find the first number divisible by 7
num = 1
while num % 7 != 0:
    num += 1
print(f"The first multiple of 7 is {num}")  # 7