## Chapter 11 – Arrays ### DIM Suppose you have a list of numbers, for instance the marks of ten people in a class. To store them in the computer you could set up a single variable for each person, but you would find them very awkward. You might decide to call the variable **Bloggs 1**, **Bloggs 2**, and so on up to **Bloggs 10**, but the program to set up these ten numbers would be rather long and boring to type in. How much nicer it would be if you could type this: ``` 5 REM this program will not work 10 FOR n=1 TO 10 20 READ Bloggs n 30 NEXT n 40 DATA 10,2,5,9,16,3,11,1,0,6 ``` Well, you can't! However, there is a mechanism by which you can apply this idea, and it uses *arrays*. An *array* is a set of variables, its *elements*, all with the same name, and distinguished only by a number (the *subscript*) written in parentheses after the name. In our example the name could be **b** and the ten variables would then be **b(1)**, **b(2)**, and so on up to **b(10)**. The *elements* of an *array* are called *subscripted variables*, as opposed to the simple variables that you are already familiar with. Before you can use an *array*, you must reserve some space for it inside the computer, and you do this using a **DIM** (for dimension) statement: ``` DIM b(10) ``` sets up an array called **b** with dimension **10** (i.e. there are 10 *subscripted variables* **b(1),...,b(10))** and initialises the 10 values to **0**. It also deletes any *array* called **b** that existed previously. (But not a simple variable. An *array* and a simple numerical variable with the same name can coexist, and there shouldn't be any confusion between them because the *array* variable always has a *subscript*). The *subscript* can be an arbitrary numerical expression, so now you can write: ``` 5 DIM b(10) 10 FOR n=1 TO 10 20 READ b(n) 30 NEXT n 40 DATA 10,2,5,9,16,3,11,1,0,6 ``` to read in the elements from a **DATA** list, or: ``` 10 FOR %n=1 TO 10 20 INPUT %m(n) 30 NEXT %n ``` to **INPUT** the elements' values by hand. Note, that in the second example there is no **DIM** statement. That's because as discussed in *Chapter 1,* the *second array is an integer array*. *Integer arrays* come *predimensioned* to a fixed 64 elements numbered **0** to **63**. Attempting