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Computer programs use variables to store information.

Variables could be used to store the score in a game, the number of cars in a car park or the cost of items on a till. They work in a similar way to algebra, where a letter in your code can stand for a number.

Creating a variable

1. Watch your teacher demonstration and then see if you can make all of the variable boxes below

Getting Started

1. Open the 'Big Wheel' mimic from the mimic menu in Flowol.
2. Explore what the mimic can do by clicking on the inputs, outputs and motors on the Status Panel.

Take a minute to understand the four different inputs.

Activity 1

To attract the crowd, use the Button 1 input to control the lighting effects on the wheel's frame. This might be a simple on/off routine but flashing sequences are more exciting. Use subroutines.

Activity 2

Use the Button 2 input to control the simple Go/Stop movement of the wheel. You could perhaps make the wheel speedup and slowdown in stages by changing the motor power.

Activity 3

Modify the flowchart you created in Activity 2 to include the safety feature of the gate so that the gate must be closed before the wheel will start (i.e. both Button 2 and Gate are on). The wheel should stop if either Button 2 is turned off, or the Gate is opened (i.e. if either Button 2 or Gate are off).

Activity 4

Use variable x to count how many times the ride is used. This could be done either by adding the increment Let instruction to the existing flowchart from Activity 3, or by creating a separate flowchart, as shown here.

Activity 5: Stopping the Wheel automatically

Construct this counting program to increase the variable y each time a seat passes the steps, i.e. each time the virtual input goes off and on.

Since there are 7 seats, each rotation of the wheel should increase the variable y by 7.

Now modify your program by introducing a decision symbol, to stop the wheel automatically after it has rotated 3 times.

Activity 6

Now that you have learned how to use the Steps input, create a subroutine which rotates the wheel and stops briefly at each of the seven seats for passengers to get on or off.

Call this subroutine twice; once at the beginning to load the wheel with passengers, and then at the end to unload.

Extension Activity: Changing the Speed of a Motor with a Variable

To keep passengers safe the wheel should gradually speed up and slow down.

While it is possible to change the speed with a sequence of Output symbols with speeds of 10%, 20%, 30% etc. it is much more compact and reusable to employ a variable.

Create the new variable s and use a speed of s% in the output symbols in the subroutines.

When running the program, observe the Wheel motor in the status panel. The size of the bar indicates the speed of the motor.