Stop Repeating Yourself: Mastering Loops in Programming

Imagine you need to print 'Hello!' 1 000 times on screen. Would you really type the same line of code one thousand times? That would take hours — and if you spotted a typo, you'd need to fix every single copy. There has to be a smarter way. Think about everyday life: a washing machine runs its drum round and round until the cycle ends. A traffic light repeats its colour sequence all day. Repetition is everywhere — and programmers have a powerful tool to handle it elegantly: the loop.

A loop is a block of code that runs more than once without you having to write it more than once. The code inside the loop is called the loop body. Each time the loop body runs, that is called one iteration. There are two main families of loop: **1. Count-controlled loops (for / repeat)** Use these when you know exactly how many times the loop should run before you write the code. A 'for' loop uses a counter variable that changes by a set amount each iteration. Example in Python-style pseudocode: for i in range(1, 6): print(i) Here, i starts at 1 and goes up to — but not including — 6, so the loop runs 5 times, printing 1, 2, 3, 4, 5. **2. Condition-controlled loops (while / until)** Use these when you do not know in advance how many times the loop should run. The loop keeps going as long as a condition is True (while loop) or until a condition becomes True (until loop). Example: count = 1 while count <= 5: print(count) count = count + 1 This does the same job as the for loop above — but imagine if the user typed in a secret number and you had to keep asking until they guessed correctly. You would not know in advance how many guesses they need, so a while loop fits perfectly. **Key rule for while loops: avoid infinite loops.** An infinite loop runs forever because the condition never becomes False. Always make sure something inside the loop changes the condition — like adding 1 to a counter — so the loop can eventually stop. **Tracing a loop** Tracing means stepping through code line by line, keeping track of each variable's value in a trace table. This lets you predict the output without running the program. You will practise this in the questions below.