Let's try to motivate why and when you would want to use an array. We will touch on the tic tac toe board but let's start with something simpler.
Suppose you are making a program to find the average score for a test. You also want to save and load the scores (later) so we can't just do a simple running average, we need to keep the scores in memory.
If this were a very small class with just three students you might get code like this.
VAR SCORE1, SCORE2, SCORE3
VAR AVERAGE_SCORE
INPUT "SCORE #1"; SCORE1
INPUT "SCORE #2"; SCORE2
INPUT "SCORE #3"; SCORE3
AVERAGE_SCORE = (SCORE1 + SCORE2 + SCORE3) / 3
PRINT "AVERAGE SCORE: ";
PRINT AVERAGE_SCORE
END
There are a number of problems with this code. The first is that we basically repeat the same INPUT code for each student. Repeating code makes your program bigger, and leaves more places to introduce bugs. We don't like that, don't repeat yourself if you can reasonably help it.
We also have a number of redundant variable names SCORE1, SCORE2, and SCORE3 that only differ by the number at the end. This is cumbersome.
This solution also doesn't scale. What if you instead need to grade a larger class of say 30 students, painful but doable. What if it was suddenly thousands of students, you would be coding for a very long time if that happened.
If you find yourself repeating code or having a bunch of nearly identical variables chances are you want an Array.
An array gives you a variable that can hold multiple copies of the same type of data. To get or set the right one you just pass it a number. The first one is at zero and it counts forward from there. If we use an array our code suddenly gets easier.
VAR NUM_STUDENTS = 30
VAR SCORES[NUM_STUDENTS]
VAR I, AVERAGE_SCORE
FOR I = 0 TO NUM_STUDENTS - 1
INPUT "SCORE #" + STR$(I + 1);SCORES[I]
NEXT I
AVERAGE_SCORE = 0
FOR I = 0 TO NUM_STUDENTS - 1
AVERAGE_SCORE = AVERAGE_SCORE + SCORES[I]
NEXT I
AVERAGE_ SCORE = AVERAGE_SCORE / NUM_STUDENTS
PRINT "AVERAGE SCORE: ";
PRINT AVERAGE_SCORE
END
Now on first glance, this code is longer and more complicated. However we can change between 3 students and 3,000 student by changing one number on the first line. Very nice, and we can use FOR loops to check each piece of data instead of checking each one manually. More complicated but much better.
Now onto the tic tac toe board we could have variables like row1col1, row1col2, all the way to row3col3, but again we are repeating variable names. Checking for a three in a row requires distinct code for every column and row. This screams out for an array. We could simply make an array like VAR BOARD[9], which would work very well. However we could also make one like VAR BOARD[3, 3]. This is a two dimensional array. You can think of it like a Excel spreadsheet that only allows one type of data. Now if you want the square in the middle it is BOARD[1, 1] . You can use one for loop to check for any three in a row values and another loop for the columns. Your code gets more maintainable and easier to handle and for large arrays vastly smaller.
I hope that all makes sense. Please let me know if my code has bugs or typeos.
Arrays are fundamental, you can't get too far without them. In the C language strings are just arrays of the char data type.
If you think of data in you program as a list of, set of, a bunch of, a grid of, or block of something it is usually best to put it in an array. It can be a list of enemy fighters or a grid of tiles on a map, or just letters in a word.
