KS2 Computing: Variables

NARRATION:You know the kind of day where first it rains, then the sun comes out, then it gets freezing cold? The weather forecast would say that the day’s weather is going to be variable. It means changeable - likely to change or vary. We can also use the word variable in computer programming when we need to measure or count something that changes, like a score, or a name, or the answer to a question, or a number. Sounds complicated? Let’s have a closer look…

Imagine you are playing a quiz. Each time you get a question correct you get a point. Yay! The trouble is, it’s hard to remember how many points you have as the quiz goes on. One solution might be to have a box and each time you get a question right you put a counter in the box. At the end of the quiz you could see how many counters there were in the box to find out your score. A computer variable acts like one of those boxes - it can store the changing information so that the rest of the program can use it.

So what would this quiz look like on a computer? As well as all the questions and answers, our quiz program would need a way to keep track of the number of right answers for each player. This is where our friend the variable score box comes in. We can give it a name to make it easier to use - let’s go with 'score'. If we break down our game program into the steps of an algorithm they might look like this: When the game starts set the quiz score to zero. When the player gets an answer correct change the score by adding one. So pretty straight forward so far, hey.

Now we have the points total stored in our variable box, we can use it for other things. Let’s say we want the player to win the game when they score 10 points. We can add these instructions to our algorithm. When the total points in the score variable equals 10, play the winner sound.

Oh come on, you should have got that one!

Let’s personalise our game. It would be fun if our quiz said hi to each player personally. The trouble is the player name will change, or vary. Yes, you guessed it, it’s time for another variable. A variable box can store words as well as numbers, and it can also get information from outside as well as from inside the program. First the program will need to ask the player a question: “What’s your name?” Once the player types in their name the program will store the information in a variable box called 'answer'. The program will then send instructions to show on screen. “Hi there, answer, are you ready for your quiz?”

Whatever is stored in the answer variable will go into the greeting. That way the same instructions can be used for any player, whatever their name might be. Clever eh?

Out in the real world, things are changing all the time. Names, numbers, scores, dates, measurements - you name it and they will probably be changing before your very eyes. This means variables are an important part of nearly all the computer programs and systems that we use every day. A good example that you might be familiar with is the dinner register at school. This information changes every day. Each morning the class teacher will count the number of pupils who are having school dinner and how many are having packed lunch. The total is then sent down to the school office, and used to tell the kitchen how many dinners and packed lunches to make for that class on that date.

Lots of schools now have computerised register systems, and the programs that control them will use variables to store all the changing information each day. The class name, the date, number of school dinners, number of packed lunches.

I don’t know about you, but I don’t think variables aren't as complicated as they first sounded, and they are a really important part of writing useful computer programs. And of course, for making sure you don’t go hungry at lunchtime!