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.1.2.4 predicates Correct answers are any integer; 1,2,3,4; say nothing and report Finished. This is a tricky question because the code doesn't do anything sensible. There are many ways to get in trouble because of overthinking the problem to try to make sense of it. For example, not only does this change the value of a variable, but the variable is the input to the procedure. Does that actually change what's entered in the input slot where the procedure is called? No, to an experienced programmer it's obvious that that won't happen. But to a second-week-of-intro-class student, nothing is obvious.2.1.3.1-3: The bug is that the first time through the loop, ANSWER is still whatever value the player last guessed (from a previous game), and if that happens to be the secret number this time too, the code in the loop is never run. Two ways to fix the bug are shown inside the definition of NUMBER GUESSING GAME, as part of the answer to 2.1, above.2.1.3.5 and later. The students will edit their NUMBER GUESSING GAME but we're starting a new one here to avoid messing up the earlier solutions. Teachers take note that, although this is presented just as an improvement to a simple game, this introduces the binary search algorithm that will be revisited several times in later units. (The algorithm isn't in the program, but in the optimal human player strategy.)

You guessed it! My secret number was22.5 ITIT:

last was too small?true1last was too small?false1You guessed it! My secret number was . It took you guesses.2There are a lot of pieces here. Maybe the most important is the LAST WAS TOO SMALL? variable, which is needed to know whether the current guess is wrong in the same direction as the previous guess. If so, a "still too small" (or big) sort of message is appropriate. If not, just plain "too small" is appropriate. The initialization of that variable has to be such that we give a plain "too small" or "too big" the first time. I knew that the value should depend on the small/bigness of the initial guess, but it gave me a headache trying to figure out which way the inequality should go, and I changed my mind a few times, until finally I just picked one, tried it out, and changed it when it turned out to be wrong. This is a perfectly okay programming technique as long as you don't forget you've made a guess that needs experimentation. The actual production of responses can be arbitrarily complicated! For example, you could add a "you guessed that already" message. For this solution I wrote three responses in each direction, meant to be given in order, and then just removed the first one from the list after using it (so you're always using the first one of the list as it then exists). If the list gets empty, for the fourth consecutive error in the same direction, just restart from the initial list of three responses. This part gives a great range for student creativity, although the big computer science idea is the variable to remember the result of the previous guess.

You guessed it! My secret number was . It took you guesses.2TIF 3.AIn TIF 3.A, note that NUMBER OF GUESSES starts at 1, not 0. Even if the REPEAT UNTIL never runs, the user still made one guess. This sort of slightly unusual initialization is a very common source of bugs.