Many people are unfamiliar with the use of arrays and they dont know what they're missing! Arrays are EXTREAMLY useful in almost any of your programs.
What is an array?
An array is essensially a group of variables of same type, put together into one group for organization and easier access. Think of it as a row of boxes, each containing a value.
Why not just declear a bunch of variables?
Have fun... Thats like buying a single ticket to Wounderland (in toronto). If you know you'll have atleast 2 variables, its cheaper to declear an array. Besides, it doesnt get preaty when you have a user defined amount of variables needed.
How to declear an array variable
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var name:array 1..10 of string |
name - the name of your variable
:array - type... says its an array
1..10 - range of the array. Here we have 10 "boxes". You can have more if you want
of string - means our "boxes" store string values. You can replace it with int, real, boolean, or w/e else you want (types for example... more on them in separate tutorial).
How to use an array
You use an array just like you would a normal variable, but you specify what "box" from your array you want to open inside the brackets after the name of the variable. name(1)
The main advantage of the array is that you can get the program to select which "box" to get the value from. Since you can put a variable inside the brakets, you can get the program to pick the index (which box).
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for i:1..10 put name(i) end for |
this way instead of saying
put name1
put name2
...
put name100
you can have a simple forloop do it for you. You can also put a couple of if statments in there to check for stuff like spelling of the name and output only if it starts with sertain letters for example.
Some array tricks - 2D arrays
Here's something that I used to scare people with right before grade10 compsci exam... "you need to know 2D arrays". People were freaking out... I donno why
Anyway, the point is that each of our little "boxes" in an array can contain a row of boxes of its own. So for each box in a row, we get another row, forming columns. This way we just created a grid (also called matrix).
it's decleared as
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var grid : array 1 .. 5, 1 .. 10 of string |
5 rows, 10 columns. Though that depends how you look at it and how you set up your forloops. I had a huge argument with my teacher of what value gous first - row or column. I dont remember what she said, but in my opinion it doesnt matter - as long as you know
How to program 2D array
Declaration (again)
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var grid : array 1 .. 5, 1 .. 10 of string |
Initialization of values (we need our array to hold something).
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for row : 1 .. 5 for column : 1 .. 10 if Rand.Real > 0.75 then grid (row, column) := "X" else grid (row, column) := "." end if end for end for |
We loop over every row and every colum and build a random map.
And now to display the contents:
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for row : 1 .. 5 for column : 1 .. 10 put grid (row, column) .. end for put "" end for |
that .. on 3rd line keeps output on same line of text
put "" forces output onto next line after a row is done
More array tricks - 3D array
same idea as before... a row of boxes inside a box thats inside a box. Now each box in a column has a row of its own going along Z axis, creating a 3D matrix to store our values. To program it, just and another forloop for the 3rd value.
Thats about where our geometric imagination ends. But programming doesnt stop here. You can create 4th and 5th and if you try hard, even 6th demention in your array. Your need for dimentions will run out faster then you'll find the limit. I cant really think of an example for a 3D array even... Maybe some record keeping setup where row is some group ID, column is name and z-axis is information about the name.
User defined size of array
You can declear array size with a variable.
var name:array 1..number of string
I dont know if that makes any difference though. As you know (and if you dont, then you will know this now) that turing converts your code to C++ before compiling it. And in C++ you cant have user defined ranges for arrays. So you just put the largest value (under 60000 +-) you know that might be used and hope your program doesnt crash
But in case your teachers care, put a variable and have a dynamic range. Just make sure to use the same variable in your for loops so that you dont go over the limit.
Conclusion
This turned out to be a LONG tutorial, but its well worth it. You'll end up using arrays in most of your programs from now on
