Chapter 9

Arrays

Sometimes, programs must store large amounts of data in memory. Say you want to store fifty different numbers in memory. You can define fifty different variables. This would be very impractical. To solve this problem we must use arrays. An array is a variable that is capable of holding several different values. Each value in the array has a number.

Program Intro_to_Arrays (input, output);

var
  Sample_Array : array [1..20] of integer;
  i : integer;

Begin

  For i := 1 to 20 do Begin
  {assign i * 5 to each element of the array}
    Sample_Array[i] := i * 5;  
  End;                         

  {now print the contents of each element}
  For i := 1 to 20 do Begin    
    Writeln(Sample_Array[i];   
  End;


End.

  Sample_Array : array [1..20] of integer;

Declaring Arrays

Arrays must be declared in the Var section. It starts with the variable name which must be a valid identifier like any other variable. It is followed by a colon. After the colon comes the "ARRAY" keyword. The range of the array must be included after the "ARRAY' keyword. In this case the range of the array is from 1 to 20. The last two elements of the declaration are the "OF" keyword and the array's datatype.

Using Arrays

Array elements are used very similarly to regular variables. The only difference is that array elements must include the element's index number.

The index number can be an immediate value like in the following example:

  Sample_Array[1] := 10;    

Or it can be a variable.

  x := 10;
  Sample_Array[x] := 10;

If the index value is out of the array's range the program will return an error message.