Lesson 11 · 11 of 20

Static arrays · Pascal

Store several values of the same type in a Pascal array: a week of temperatures, with the average and the hottest day.

Pascal · Static arrays in DMarlon Studio: the example's code and its output in the terminal

An array holds several values of the same type under one name. It is declared with its indexes: array[1..7] of Integer is seven integers numbered 1 to 7. It is static: its size is fixed when the program is compiled and never changes.

Days is a constant array, with its values in brackets, and temps is a variable that starts with the week's temperatures. Each element is reached by its index in square brackets: temps[4] := 20 corrects Thursday.

`Low` and `High` give the first and last index, and `Length` the number of elements. With them the for loop walks the array without hard-coded numbers, and keeps working if the size changes.

Inside the loop three things happen: each day is printed with its temperature, added to total, and hottest remembers the index of the hottest day so far. At the end, total / Length(temps) gives the average.

Using an index that does not exist, such as temps[8], is a mistake. With a constant index the compiler already warns you; with a variable, turn on run-time checking with {$R+} at the top of the program.

Code · main.pas

program main;// A constant array: the names of the days.const  Days: array[1..7] of String = ('Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun');// A variable array of 7 integers, with initial values.var  temps: array[1..7] of Integer = (18, 21, 24, 19, 26, 28, 22);  i, hottest, total: Integer;begin  temps[4] := 20;  // change one element  total := 0;  hottest := 1;  // Low and High give the first and last index.  for i := Low(temps) to High(temps) do  begin    WriteLn(Days[i], ': ', temps[i]:3, ' C');    total := total + temps[i];    if temps[i] > temps[hottest] then      hottest := i;  end;  WriteLn('Average: ', total / Length(temps):0:1, ' C');  WriteLn('Hottest day: ', Days[hottest], ' (', temps[hottest], ' C)');end.

Output · fpc main.pas && ./main

Mon:  18 C
Tue:  21 C
Wed:  24 C
Thu:  20 C
Fri:  26 C
Sat:  28 C
Sun:  22 C
Average: 22.7 C
Hottest day: Sat (28 C)

Key points

array[1..7] of Integer declares seven integers.
a[i] reads or changes element i.
Low, High and Length give the bounds and the size.
A static array never changes size.

Exercise

Add a rain array with the litres of rain for each day and print how many days it rained and which day was the wettest.