Arrays - Right

An array is a collection of fixed size of data items of the same type. The benefit is that you can store a whole set of values under 1 single name only. You can refer to each one separately, as each value is stored in a separate cell.

The general definition is

var

arrayname:array [indextype] of type;

You can e.g. create an array storing 100 integers. The declaration would be array [1.100] of integer; You can specify this as a type or directly in the variable specification part.

As type declaration:

type

arrint=array[1..100] of integer;

var

arrint1:arrint;

As declaration in variable part:

var

arrint:array[1..100] of integer;

Important notes:

The elements of an array must be of the same type
The index may be a subrange of any ordinal type, i.e., integer, char, boolean, enumerated type. The subrange does not have to start from the first value of the underlying type. The index cannot be real.
It is important not to use a value in an array-index before it is initialized, as it stores junk then.

Examples:

1. To print an array from the reverse onto the screen.

program reverseorder(input,output);

type

arraytype = array [1..10] of integer;

var

arr:arraytype;

i:integer;

begin

for i:=1 to 10 do

arr[i]:=i;

for i:=10 downto 1 do

writeln(arr[i]);

end.

2. To read values into an array

var

arr:array[1..4] of real;

i:integer;

begin

for i:=1 to 4 do

readln(arr[i])

end.

You can also have arrays of arrays. Moreover, there is another possibility 'packed array of char'. It is very useful, as you will see.

Packed array of Char

Rules:

The word 'array' must be preceded by the word 'packed'.

The lower index value must be 1.

Lets explain it with an example:

type

charstring = packed array [1..5] of char;

var

name1,name2,name3 : charstring;

begin

name1:='Susan';

name2:='Mary '; {Note that you could not have written 'Mary' as the size must be 5.}

name3:=name1;

writeln(name1);

if name1>name2 then ..... {you can compare them according to the alphabetical ordering}

end.

Disadvantage:

Furthermore, you have to supply spaces whenever your input is smaller than the specified size;

You can also have arrays of packed arrays.

Multidimensional Arrays

Arrays of arrays are called multidimensional arrays. There could arise any reason for using this.

General form of declaration: arraytype = array [index1, index2, ... , indexn] of elementtype;

This is the same as array [index1] of array [index2] of .. array[indexn] of elementtype;

Example:

A : array [ 1..5,10..12,6..9,0..3] of integer;

Then they are referred to as: A[1,10,3,0] and can be used as simple integers.

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