Page 215 - Learn To Program With Scratch

Unscramble

Unscramble .sb2 Our last example presents another word game that is a little more challeng-
ing to play. We’ll start with an English word, scramble its letters, and ask the
player to guess the original word.
Let’s start by creating a procedure that rearranges the characters of a
given string in random order. The caller sets the input string (strIn), and
the procedure, named Randomize, modifies it so that its characters are
shuffled around, as illustrated in Figure 8-10.

Randomize

abcdefg strIn cbeagdf

Figure 8-10: Illustrating the Randomize procedure

We’ll pick a random letter from strIn and append that letter to a tempo-
rary string, str1. (This temporary string, which starts off empty, is where we’ll
store the scrambled word as we build it.) We’ll then remove that letter from
strIn so we don’t reuse it and repeat the whole process until strIn is empty.
The Randomize procedure implements these steps as shown in Figure 8-11.










Figure 8-11: The Randomize procedure
First, Randomize sets len to the length of the input string, strIn, and
empties the temporary string, str1 u. The procedure then starts a repeat
loop to assemble the scrambled word v. The repeat count equals the length
of the input string. For each loop iteration, we pick a random position in
strIn w and append that letter to str1 x. Note that we used length of in step
w because strIn and its length will change inside the loop. After that, we
call a procedure named Remove to delete the character we just used from
strIn y. When the loop finishes shuffling letters around, strIn is set to the
scrambled word (str1) z.

String Processing 193

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