Loops: Repeating Work

Doing Things Again and Again

Computers are excellent at repetition. A loop runs the same block of code many times so you do not have to write it out by hand.

The for Loop

A for loop walks through a sequence of items, one at a time. The range() function produces a sequence of numbers.

for i in range(5):
    print("Count:", i)

This prints the numbers 0, 1, 2, 3, 4. Note that range(5) starts at 0 and stops before 5, giving exactly five values.

You can also loop directly over a list of items.

subjects = ["Math", "Accounting", "ICT"]
for subject in subjects:
    print(f"Studying {subject}")

The while Loop

A while loop keeps running as long as a condition stays True. Use it when you do not know in advance how many repetitions you need.

count = 1
while count <= 3:
    print("Attempt", count)
    count = count + 1

The line count = count + 1 is essential. Without it the condition would always be True and the loop would run forever — an infinite loop.

break and continue

• break stops the loop immediately.
• continue skips the rest of the current pass and jumps to the next one.

for n in range(1, 10):
    if n == 5:
        break          # stop entirely when n is 5
    if n % 2 == 0:
        continue       # skip even numbers
    print(n)           # prints 1, then 3

Accumulating a Result

A very common pattern is building up a total inside a loop.

total = 0
for mark in [70, 85, 90]:
    total = total + mark
print("Total marks:", total)  # 245

If your program seems frozen, you may have created an infinite loop. Always make sure the loop condition can eventually become False.