A problem and a simple set of instructions to solve it. A good starting point for a game but also for coding.
One of the two players is blindfolded and must pin a paper tail in the right place. He can do only few actions: go up, down, left or right and finally pin the tail.
The other player can see the drawing and must help giving instructions.

Let’s compare with computers

A computer is dumb and can do a limited set of actions. You may think your computer or smartphone is very powerful but the core is still a poor dumb processor moving bits and making sums.

The only way to make a computer work is giving it instructions. So programmers must use the set of available actions and combine them in different ways thus making more complex actions.

Playing the game

When kids play the game, they freely move the tail in front of the drawing and unknowingly add some extra commands, like stop or go on.
These extra commands are actually a way to communicate to the blindfolded kid that an action must be repated until a certain condition is reached.

So we know the concept of loop. Let’s make an example, but to make it undestandable we have to use a grid made of squares. It will also make it compatible with computers later.

  A B C D E F G H
1 T              
3           D    

At the beginning Tail (T) is in position (A,1) while the Donkey’s back (D) is in position (F,3).
The commands for the blindfolded player will be: right, right, right, right, right, down, down.

But we can also generalize these commands, we just have to think about what happens in the mind of the observer:

if D is on the right of T:
    while D is on the right:
        move T to the right
else if D is on the left of T:
    while D is on the left:
        move T to the left
if D is below T:
    while D is below:
        move T down
else if D is above T:
    while D is above:
        move T up

As you can see this is not a solution to a single problem, but it is a generic approach that can be used for any position of T and D.

If you think about it, we can rewrite the same instructions in much less lines, but optimization deserves a whole chapter on its own.

Image from WikiMedia Commons