There is something lacking in our example quizz-program, in that you are only allowed to guess once. That's rather unfair, especially considering the odds on getting it right the first time (1:10). So, what we could perhaps do to make the program a little more fun, is to allow the user to guess more than once. How do we do that? We could, of course, type the lines a few times more, so that the question is asked a few times more, like so

But that is rather inefficient, especially considering that we do not know in advance how soon the user will guess the number, so we don't know how often we need to repeat it. What we need is something which automatically repeats the question until the answer is correct. In other words, we need a conditional loop. A conditional loop repeats itself until a certain expression becomes true - in our example this would be A = B.

There are usually two main types of conditional loops. One where the condition is tested at the beginning of the loop, and one where the condition is tested at the end of the loop. The most unsurprising loop is the repeat ... until (expression = true) loop. This does just as you would expect (I hope at least that you expect what it does) - it repeats the lines of code inbetween the repeat and until statements until the expression between the brackets becomes true. Here's it applied to our example program:

This does exactly what we need. It repeats everything between repeat and until, until the expression A = B is true - in other words, that the guessed number is the same as the randomly picked number; then it continues with the rest of the program, which prints that the game is over, and then ends. Also notice that it is much clearer to see how the structure of your program is when you right-indent everything that is within a control of flow statement.

We can enhance our little program a little by also counting the number of turns it took the user to guess the correct number, by changing the last lines to so:

Each time the program runs through the repeat ... until loop, e.g. each time the user attempts another guess, the variable turns is assigned the value of itself + 1. So if turns was 2 before, when the computer performs the line turns = turns + 1, then it assigns 2 + 1 (=3) to turns. So from then on, turns is 3. When the loop is over and the number is guessed, this value is then printed in the penultimate line.

To give another example, we could also add a hint option, so that the user will not have to guess blindly, by letting the computer tell the user whether he or she is close to the correct number or not ('warm' or 'not even close...'), by changing the lines between 'else' and 'endif' like so:

The absolute number of the difference between a and b, or abs(a - b) for short, will give us the difference between a and b, whether a is bigger than b or b is bigger than a. We can then check if the difference is smaller than 3, in which case we can add a hint indicating that the user is not far off with his guess; or, if difference isn't smaller than 3, indicate that the user should radically alter his guess.  

By now, you've learned about some of the most important concepts of programming. "Really?", I can imagine you thinking right now. But yes, really. You've learned the basics which allow a program to react to input from the user in a dynamic way, by using the input as a parameter in boolean logic and using the boolean logic to steer the computer through different parts of the program in response. 

This means that of any given interactive situation, if you understand which input is needed to create a desired output, and which logic is needed in combination with which actions to achieve this, then you can write a program for that situation that interacts according to the way you want it to. That sounds very impressive, doesn't it? In less impressive words, basically you can now write a program that does something you want it to do, as long as you understand exactly what you want it to do. Again, this is important. There is a favourite bit from Douglas Adams' Hitchhiker's Guide to the Galaxy series where humans build a computer that can build a computer which can answer the question "What is the meaning of life?". After generations of work, the computer is finally complete, and it comes up with the answer "42". The humans are puzzled and question the computer, which dryly answers "Well, are you certain you understood the question?". If computers reply with something you don't understand, this usually means that you have not understood the question, and need to rethink your program. 

Here is the complete source so far for the quizz-program, which you can type in and play around with on your own Playstation 2:

Notice a few differences to the code you've seen so far. I've left out the string variables which I used to store text that I was going to print for the user, because this way it's a little clearer to follow the program in the source and makes the source shorter - which is nice for those of you who use the controller to type this all in (it's doable, but you wouldn't want to write "War and Peace" with it, now would you?). Also, instead of print I used the short version ?, which means the same thing, and instead of using endif, I used fi, which also means the same thing, for the same reasons. The structure of the program has changed slightly too - the position of telling the user that the game has ended has, among others, changed. Study the program a little and see if you can understand if and why it still works. 

Finally, notice that I added the int() function - the ran function returns a random number, but this is a real number, i.e. a number that has a fractional part. But when I ask someone to guess a number between 0 and 10, they'd be rather upset if I told them they were wrong all the time, and then when they finally give up I tell them the number was 6.81742. That'd be as hard as guessing a number between 0 and 100.000! To make it even more precise, I added 1 to the number (now you can also have 0) and made it a number between 0 and 9, so that with the added 1 you can now only get numbers that are really between 0 and 10, not including either 0 or 10.

So, here we stand, a little dazzled, but also a little wizer. Where to now? Well, from here onward, its case study time! We'll look at some real-life programming problems and work our way through until we've created a bunch of routines that will provide a good foundation for any program you may wish to write yourself later on. The first case we'll be studying is writing routines that read complex combinations of commands from your controller, such as games like Tekken do, and we'll work our way towards something resembling the "Tekken Practice Mode" in Tekken Tag (without the graphics, naturally). After that, or perhaps even at the same time as a paralel thread, we'll do some graphics' stuff to make you're user interface (that which the user of your program sees and uses to interact with your program) a little flashier. 

(c) 2001 Arwin van Arum

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