The use of arrays
Using arrays to structure data
Sometimes a programmer needs to store a lot of related dataValues, typically letters or numbers..
Example
A game might record the scores achieved by players.
One way to do this would be to declare a variableA memory location within a computer program where values are stored. for each score. So for ten scores, the game program would require ten variables:
score1
score2
score3And so on, up to score10
While certainly possible, this is not a practical method of recording this data. Suppose the program needed to record 100 scores? 100 variables would be required!
A better method is to use an arrayA set of data values of the same type, stored in a sequence in a computer program. Also known as a list. . An array is a data structure that holds similar, related data. An array is like a collection of boxes, each of which is called an elementAn individual component of an array.. Each element has a position in the array, and can hold a value. The data in an array must all be of the same data typeIn computer programming, data is divided up and organised according to type, eg numbers, characters and Boolean..
This way, all data is stored under one identifierA name given to a part of a program, such as a variable, constant, function, procedure or module.. For example, the array called “score” could contain the following ten scores for a player:
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| 100 | 110 | 85 | 80 | 92 | 72 | 66 | 98 | 100 | 120 |
| 0 | 100 |
|---|---|
| 1 | 110 |
| 2 | 85 |
| 3 | 80 |
| 4 | 92 |
| 5 | 72 |
| 6 | 66 |
| 7 | 98 |
| 8 | 100 |
| 9 | 120 |
Declaring an array
Before an array can be used, it must be declared. To declare an array it must be given at least two properties:
- an identifier
- a size (the number of elements it will hold)
Example
array score[9] - would declare an array with ten elements (zero to nine)
Note - some programming languages also require the array's data type to be declared.
Once declared, the name and structure of an array cannot be changed.
Assigning values to an array
Values are assigned to an element in an array by referring to the element's position.
Example
score[0] = 100 - would assign the value 100 to the first element in the array
Values in elements can be overwritten at any point, simply by assigning another value to that element.
Retrieving values from an array
Values are retrieved from an element in the array by again referring to the element's position.
Example
print(score[7]) - would display the eighth value held in the array. In the above example, the value would be 98
Two-dimensional arrays
A two-dimensional array can hold more than one set of data. This type of array is like a table, with data held in rows and columns.
The following array would hold ten scores for two players. The first player (0) has data stored in the first row. The second player (1) has data stored in the second row.
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | |
| 0 | 100 | 110 | 85 | 80 | 92 | 72 | 66 | 98 | 100 | 120 |
| 1 | 90 | 99 | 102 | 88 | 78 | 100 | 67 | 120 | 88 | 105 |
| 0 | |
| 0 | 100 |
| 1 | 110 |
| 2 | 85 |
| 3 | 80 |
| 4 | 92 |
| 5 | 72 |
| 6 | 66 |
| 7 | 98 |
| 8 | 100 |
| 9 | 120 |
| 1 | |
| 0 | 90 |
| 1 | 99 |
| 2 | 102 |
| 3 | 88 |
| 4 | 78 |
| 5 | 100 |
| 6 | 67 |
| 7 | 120 |
| 8 | 88 |
| 9 | 105 |
A two-dimensional array is declared using two values - the number of rows and the number of columns.
Example
array score = [1,9] - would give an array with two rows and ten columns
Data is assigned or retrieved by referring to an element's row and column number. For example:
score[0,1] = 110
print(score[1,4]) - would display the score 78
