Combining Code: Sequences, Selection and Repetition

🎮 Imagine a video game character who walks forward, checks if there is a wall ahead, and keeps moving until it reaches a door. That character is following a program — and that program uses three powerful ideas working together: sequence (doing things in order), selection (making decisions) and repetition (looping actions). Almost every program ever written uses all three. Today you will discover how they combine to solve real problems — and how to spot when something goes wrong.

Let's define each idea precisely. A sequence is a set of instructions carried out one after another, in a fixed order — like a recipe. Selection means the program tests a condition and chooses one of two paths: if the condition is true it does one thing, else it does something different. Repetition (also called a loop) means a block of instructions is executed over and over — either a fixed number of times or until a condition changes. Each structure is useful alone, but combining them lets you build programs that can respond to changing situations and handle complex tasks.

When you combine all three, something powerful happens. Picture a sprite collecting stars in a maze. The program loops (repetition) until all stars are collected. Inside the loop, it moves forward (sequence), then checks whether it has hit a wall (selection) — if yes, it turns; if no, it keeps going. The loop keeps the whole thing running again and again. The selection reacts to what is happening. The sequence makes sure each action happens in the right order. Remove any one structure and the program breaks. They are stronger together. 💪

Now let's think about logical reasoning — using what you know about how programs work to track down bugs 🐛. A bug is an error that makes the program behave unexpectedly. There are two main types. A syntax error means the blocks are connected in a way the computer cannot understand — like missing a block altogether. A logic error means the blocks run without crashing, but the result is wrong — for example, your sprite turns left when it should turn right. To debug, trace through the program step by step in your head, checking what each block does and whether the order and conditions are correct.

Here is a step-by-step algorithm for a star-collecting sprite, written in plain English so you could draw it as a flowchart or build it in blocks. Follow the order carefully — this is exactly how a programmer thinks before touching any code. Notice how sequence, selection and repetition each play a clear role at specific points in the design.