Array
Content of the lesson:
- Characteristic of the Array Data Type
- Defining the Array Data Type
- Filling and Listing an Array
- Inserting any Number of Elements into Array
- Program for Payments
Characteristic of Array Data Type
An array can be described as a variable which can store more values (not only one).
It is a data structure which can store a sequence of values. An empty array can be illustrated as the following image:
As you see, the array is empty (there is nothing in the boxes) but the translator usually assigns them with a value after launching the program (usually using the value 0 in case of integers). Without any action, your array would look like the following one:
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
You can fill such a data structure with any numbers:
| 5 | 8 | 7889 | 1 | 29 | 9 | 126 | 6656 | 778 | 2 |
It is a structure which contains several places to store values. A good analogy is for example
- a row from squared paper if you write a whole number in each box (an array of integers)
- a row of drawers which contain lists of paper where you can write anything (an array of strings)
The previous array figures as one variable which contains 10 numbers. How to fill an array and use it?
We will use the analogy of squared paper - imagine you have cut away a row of 10 boxes. You want your program to write proper numbers in these boxes, so you have to tell it something like this:
- Write the number 5 into the first box.
- Write the number 8 into the second box.
- Write the number 7889 into the third box.
- ...
- Write the number 2 into the tenth box.
You can see that every box has its identifier (a number) and this number is called an index. Using an index you can identify the right box. This situation is illustrated in the following table (at index 5 is stored value 29):
| index | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| value | 5 | 8 | 7889 | 1 | 29 | 9 | 126 | 6656 | 778 | 2 |
Defining the Array Data Type
Declaration of an array of n items should look like this one:
type
pole = array[1..n]of integer;
After declaring this data type, you can declare a variable of this type:
type
pole = array[1..n]of integer;
var
p:pole;
In case you want to use an array of 10 items in your program, you should use:
type
pole = array[1..10]of integer;
var
p:pole;
Filling and Listing an Array
If you want to insert a value inside the array p on a particular place, you can use this command:
p[i]:=hodnota;
The previous notation says that hodnota will be inserted at the i position inside the p array. Example of inserting value 5 in the first item.
type
pole = array[1..10]of integer;
var
p:pole;
begin
p[1]:=5;
end.
If you want to fill the whole array using previous values, you will have to assign the value to every item separately.
type
pole = array[1..10]of integer;
var
p:pole;
begin
p[1]:=5;
p[2]:=8;
p[3]:=7889;
p[4]:=1;
p[5]:=29;
p[6]:=9;
p[7]:=126;
p[8]:=6656;
p[9]:=778;
p[10]:=2;
end.
What are the advantages and disadvantages of this procedure? User is not allowed to enter any values, only the programmer can do it. If you want a user to be able to enter his values, you should change the example:
type
pole = array[1..10]of integer;
var
p:pole;
begin
readln(p[1]);
readln(p[2]);
readln(p[3]);
readln(p[4]);
readln(p[5]);
readln(p[6]);
readln(p[7]);
readln(p[8]);
readln(p[9]);
readln(p[10]);
end.
This procedure has also one disadvantage - user cannot insert as many variables as he want. On the top of that, imagine a situation when you want to insert 100 values for example... The second problem can be gracefully solved using a FOR cycle.
Program NaplneniAVypisPole;
type pole = array[1..10]of integer;
var p:pole;
i:integer;
begin
for i:=1 to 10 do
begin
readln(p[i]);
end;
for i:=1 to 10 do
begin
writeln(p[i]);
end;
readln;
end.
Filling an array and writing its content with the possibility to enter the number or items
Program NaplneniAVypisPole;
type pole = array[1..5000]of integer;
var p:pole;
i, pocet:integer;
begin
writeln('Enter the number of items (1-5000)');
readln(pocet);
while ((pocet<1) or (pocet>5000)) do
begin
writeln('Enter the number of items
again:');
readln(pocet);
end;
for i:=1 to pocet do
begin
readln(p[i]);
end;
for i:=1 to pocet do
begin
writeln(p[i]);
end;
readln;
end.
Filling an array and writing its content with the possibility to enter the number or items and using a constant
Program NaplneniAVypisPole;
const n = 5000;
type pole = array[1..5000]of integer;
var p:pole;
i, pocet:integer;
begin
writeln('Enter the number of items (1-',n,')');
readln(pocet);
while ((pocet<1) or (pocet>n)) do
begin
writeln('Enter the number of items
again:');
readln(pocet);
end;
for i:=1 to pocet do
begin
readln(p[i]);
end;
for i:=1 to pocet do
begin
writeln(p[i]);
end;
readln;
end.
Program for Payments
Write a program for entering payments for employees in a company. It should accept payments until user enters 0 (this will be the end of inserting). After getting all values the program should write them and show their number.
Program Vyplaty;
const n = 1000;
type pole = array[1..n]of integer;
var p:pole;
i,pocet,vyplata:integer;
begin
writeln('Enter payments (0 for end):');
vyplata:=1;
i:=1;
while (vyplata<>0) do
begin
readln(vyplata);
p[i]:=vyplata;
i:=i+1;
end;
pocet:=i-2;
writeln('Entered payments:);
for i:=1 to pocet do
begin
writeln(p[i],' ');
end;
writeln('Count of entered payments is ',pocet);
readln;
end.
The program is not completely correct. Try to solve any mistake you find.
Program for Payments, Second Version
Create a program for inserting payments for employees (the maximum number is 100 payments). Then the program should write all payments, count an arithmetic mean of payments and write the lowest and highest values. It should also write the final sum needed for all payments. Try to format the output of payments to separate values with the comma character and to write a dot behind the last payment value.
Additional Texts
Questions
- What does the term array mean in Pascal?
- Try to illustrate the appearance of the array structure.
- How can you declare the array data type?
- What are the advantages of the array data type?
- Write a source code which will fill an array of n items with values gained from an user.