FACULDADE DE E NGENHARIA DA U NIVERSIDADE DO P ORTO

Exercises on Lazarus

Andry Maykol Pinto, Paulo Portugal and José Faria

Informática Industrial

February 18, 2021

© INFI 2020, V1
 Exercises on Lazarus

Andry Maykol Pinto, Paulo Portugal and José Faria

Informática Industrial

February 18, 2021

Contents

1 Exercises on Free Pascal: Part 1 1

1.1 New application on Lazarus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Adding a series of numbers . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.2 Real and string manipulations . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.3 String . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.4 String compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.5 Counting letters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.6 String manipulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.7 Concatenate and print different data types . . . . . . . . . . . . . . . . . 5
1.2.8 Relational expressions and IF statement . . . . . . . . . . . . . . . . . . 6
1.2.9 Quotient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.10 Arithmetic expression . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.11 Arithmetic expression . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.12 Boolean expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3.1 IF and ELSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3.2 CASE and Sub-range . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3.3 FOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3.4 Twin FOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.5 FOR and Random . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.6 While . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.7 Nasty while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2 Exercises on Free Pascal: Part 2 11

2.0.1 Creating a structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.0.2 Implementation clues . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.0.3 TTimers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

i
ii CONTENTS
Chapter 1

Exercises on Free Pascal: Part 1

A set of exercises are recommended to students. These exercises will cover all fundamentals of
the free pascal programming language including:

• data types;

• data manipulation;

• statements.

1.1 New application on Lazarus

For each exercise you will be invited to create a new application. For doing this, please select
”File” then ”New”. After this, a new window will appear in which you should select: ”Project”
and ”Application”, see figure 1.1

Figure 1.1: Lazarus: new application

1
 2 Exercises on Free Pascal: Part 1

After saving the project (”Save All”), you can notice that there is a Project1(.lpi) and Unit1(.pas),
and you are invited to change the filenames of both.

In the Unit1.pas you will encounter:

1 u n i t Unit1 ;
2

3 {$mode objfpc}{$H+}
4

5 interface
6

7 uses
8 C l a s s e s , S y s U t i l s , Forms , C o n t r o l s , G r a p h i c s , D i a l o g s ;
9

10 type
11 TForm1 = c l a s s ( TForm )
12 private
13

14 public
15

16 end ;
17

18 var
19 Form1 : TForm1 ;
20

21 implementation
22

23 {$R *.lfm}
24

25 end .
code/exampleApplication.txt

1.2 Data Types

The first module will be related to manipulation of variables of different data types.

• integer;

• real;
1.2 Data Types 3

• boolean;

• strings.

1.2.1 Adding a series of numbers

In this exercise you will add two variables to understand the difference between different data
types and how you can manipulate them.

Follow the figure 1.2 by adding to the Form1:

• BT_Calculate: TButton;

• Ed_Numb1: TEdit;

• Ed_Numb2: TEdit;

• Label_Numb1: TLabel;

• Label_Numb2: TLabel;

• Label_Result: TLabel;

• Memo_ShowResult: TMemo;

By double-clicking on the Button, you will create automatically the event: ”procedure BT_CalculateClick(Sen
TObject);”. This event will happen every time that the button is pressed.

Figure 1.2: Lazarus: new application

 4 Exercises on Free Pascal: Part 1

Now, you want to code your program that will add two integer numbers using Editboxes as
inputs and the Memobox as output. Several questions arrive:

• The structure of a typical ”procedure”.

• Declaration of local variables.

• Assignment operator.

• Adding operator.

• String versus integer.

• ”StrToInt” does what? And about the ”StrToIntDef”.

• Printing the result in the MemoBox.

The code for the procedure is:

1 procedure TForm1 . B T _ C a l c u l a t e C l i c k ( S e n d e r : T O b j e c t ) ;
2 var
3 numb1 : integer ;
4 numb2 : integer ;
5 r e s _ c a l : integer = 0 ;
6

7 begin
8 numb1 : = S t r T o I n t D e f ( Ed_Numb1 . Text , 0 ) ;
9 numb2 : = S t r T o I n t D e f ( Ed_Numb2 . Text , 0 ) ;
10 r e s _ c a l : = numb1 + numb2 ;
11

12 Memo_ShowResult . C l e a r ;
13 Memo_ShowResult . Append ( I n t T o S t r ( r e s _ c a l ) ) ;
14 end ;
code/ex1Adding.txt

1.2.2 Real and string manipulations

Consider the same example but with :

1. real data-type. The ”res_cal” should be divided by 2.5.

2. string data-type.

• by ”adding” two strings: ”INFI” and ” 2020”.

1.2 Data Types 5

• print the size of ”res_cal” which should be a string.

• verify if ”res_cal” contains the text ”FI”.

• locate the index of ”20” (the location of the first appearance in the string).

1.2.3 String

Read a string and write it out with a space between each adjacent pair of characters. Example:

• Enter: waffle

• Print: w a f f l e

1.2.4 String compare

Read a password P using an EditBox, then clear the MemoBox and repeatedly read password
guesses in the other EditBox until the password P is entered. Example:

• Enter password: pineapple

• Password: apple

• Print: wrong!

1.2.5 Counting letters

Write a program that reads a single line of input text, and determines which letter from A to Z
appears most frequently in the input text. You should ignore case, considering ”a” and ”A” to be
the same letter.

1.2.6 String manipulations

Write a function capitalize(s: string): string that capitalizes the first letter of every word in a string,
where words are separated by one or more spaces.

1.2.7 Concatenate and print different data types

Declare two string variables: Name and Surname. Declare an integer variable: Age. Use three
EditBoxes: to assign to Name and Surname your name and surname and, your age to Age. Use a
”ShowMessage” to display the text ”My name is $name $surname. I am $age years old.” after the
button is pressed.
6 Exercises on Free Pascal: Part 1

1.2.8 Relational expressions and IF statement

Read two integers X and Y and report which is greater (or that they are equal).
Example:

• Enter X: 4

• Enter Y: 6

• Print: Y is greater

1.2.9 Quotient
Read two integers X and Y, and print their quotient if X is exactly divisible by Y, or ”indivisible”
otherwise. Example:

• Enter X: 10

• Enter Y: 3

• indivisible

1.2.10 Arithmetic expression

Read two reals X and Y and print the result of:

• (X / Y)

• (X * Y)

• (X div Y)

• (X mod Y)

1.2.11 Arithmetic expression

Write a program that prompts the user to enter the radius of a circle (integer) and outputs the
circumference and the area. Both amounts should be displayed to two decimal places

1.2.12 Boolean expressions

Read two booleans X and Y and print the result of:

• (X AND Y)

• (X OR Y)

• (NOT X)

• (X XOR Y)
 1.3 Statements 7

1.3 Statements
1.3.1 IF and ELSE

Read three numbers and write whether or not they can form a triangle. Note - to form the sides
of a triangle, each value must be less than the sum of the other two. You should categorize the
triangle into: ”EQUILÁTERO”, ”ISÓSCELES” or ”ESCALENO”.

1 if (A < B AND (B < A + C) AND (C < A + B) then

2 begin
3 { (’Os numeros formam os lados de um triangulo
’); }
4 if (A = B) and (B = C) then
5 { (’equilatero ’) }
6 else
7 if (A <> B) and (A <> C) and (B <> C) then
8 { (’escaleno’) }
9 else
10 { (’isosceles’); }
11 end
12 else
13 { nao triangulo }
code/ex3IF.txt

1.3.2 CASE and Sub-range

Read a year from 1980 to 2020 using the EditBox. Print the decade that it was in. Example:

• Year: 1995

• Print: 1995 was in the 1990s

1.3.3 FOR

Ask the user for a number N, then write the word ”strawberries” N times. Example:

• How many strawberries: 3

• strawberries

• strawberries

• strawberries
 8 Exercises on Free Pascal: Part 1

1.3.4 Twin FOR

Read a number N, then print an N x N triangle of asterisks.

• Enter N: 6

• *

• **

• ***

• ...

• ******

1.3.5 FOR and Random

Simulate coin flips, printing an ”H” each time the coin falls on heads and ”T” each time it falls on
tails. Once you reach the third H, stop and write how many coins were flipped. Example:

• HTTTHTH

• 7 flips

• ===

1.3.6 While

Write the same loop using while instead of for.

1 procedure TForm1 . B T _ C a l c u l a t e C l i c k ( S e n d e r : T O b j e c t ) ;
2 var
3 numb1 : integer ;
4 numb2 : integer ;
5 r e s _ c a l : integer = 0 ;
6 i : integer ;
7

8 begin
9 Memo_ShowResult . C l e a r ;
10

11 for i : = 1 to 5 do
12 Memo_ShowResult . Append ( I n t T o S t r ( i ) ) ;
13 end ;
code/ex2While.txt
1.3 Statements 9

1.3.7 Nasty while

Update the code of the previous exercise. The ”res_cal” should be printed in the MemoBox while
”numb2 < 10 ’. Consider the value of ”res_cal” as ”numb1 * i”. What happened?
10 Exercises on Free Pascal: Part 1
Chapter 2

Exercises on Free Pascal: Part 2

These exercises will cover the following topics: record data type; procedures; functions and,
passing arguments by value or reference.

2.0.1 Creating a structure

Follow the figure 2.1 to create a new application in Lazarus:

• BT_AddOrder: TButton;

• CB_PartType: TComboBox;

• CB_Destination: TComboBox;

• Ed_Numb1: TEdit;

• Label_Numb1: TLabel;

Figure 2.1: Lazarus: example for record data types

11
 12 Exercises on Free Pascal: Part 2

• Label_PartType: TLabel;

• Label_Destination: TLabel;

• Label_Result: TLabel;

• Memo_ShowResult: TMemo;

This exercise introduces the ”TComboBox”. Please explore this component, in particular, the
”items” and ”itemIdex”. Note that you can access the item that was selected by the user with both
properties: ”CB_PartType.items[CB_PartType.ItemIndex]”. We want to create a structure called
”TOrder” which will be formed by the following members:

• id : integer;

• fromType: tPartType;

• destination : tRouter;

2.0.1.1 Data types: record, enumerated and sub-range

By pressing the TButton, a new instance of ”TOrder” should be locally created and printed in the
TMemoBox. Create a record data type (”TOrder”) using the:

• ”id” variable that can assume an integer value (no repetition should be allowed).

• ”tPartType” variable that can assume a value of ”A”, ”B”, ... or ”G”;

• ”tRouter” variable that can assume a value within the range 0 .. 7;

2.0.1.2 With statement

Use the ”With” statement for printing each order that is created when the TButton is pressed.

Try yourself and then compare with the following code. Analyze and discuss the differences.

1 u n i t Unit1 ;
2

3 {$mode objfpc}{$H+}
4

5 interface
6

7 uses
8 C l a s s e s , S y s U t i l s , Forms , C o n t r o l s , G r a p h i c s , D i a l o g s ,
StdCtrls ;
 Exercises on Free Pascal: Part 2 13

10 type
11 tRouter = 0 . . 7 ;
12 t P a r t T y p e = ( P a r t A = 0 , P a r t B , P a r t C , PartD , P a r t E ,
PartF , PartG ) ;
13 TOrder = record
14 id : integer ;
15 PartType : tPartType ;
16 Route : tRouter ;
17 end ;
18

19 { TForm1 }
20

21 TForm1 = c l a s s ( TForm )
22 BT_AddOrder : T B u t t o n ;
23 CB_PartType : TComboBox ;
24 C B _ D e s t i n a t i o n : TComboBox ;
25 Ed_Numb1 : T E d i t ;
26 Label_Numb1 : T L a b e l ;
27 Label_PartType : TLabel ;
28 L a b e l _ D e s t i n a t i o n : TLabel ;
29 L a b e l _ R e s u l t : TLabel ;
30 Memo_ShowResult : TMemo ;
31 procedure BT_AddOrderClick ( S e n d e r : T O b j e c t ) ;
32 private
33

34 public
35

36 end ;
37

38 var
39 Form1 : TForm1 ;
40

41 implementation
42

43 {$R *.lfm}
44

45 { TForm1 }
46
 14 Exercises on Free Pascal: Part 2

47 procedure TForm1 . BT_AddOrderClick ( S e n d e r : T O b j e c t ) ;

48 var
49 l o c a l O r d e r : TOrder ;
50 begin
51 Randomize ;
52 localOrder . id : = Random ( 1 0 0 0 ) ;
53 l o c a l O r d e r . P a r t T y p e : = t P a r t T y p e ( CB_PartType . I t e m I n d e x ) ;
54 l o c a l O r d e r . Route :=
StrToInt ( CB_Destination . Items [ CB_Destination . ItemIndex ] ) ;
55

56 With l o c a l O r d e r do
57 Begin
58 Memo_ShowResult . C l e a r ;
59 Memo_ShowResult . Append ( ’ID: ’+ I n t T o S t r ( i d ) ) ;
60 Memo_ShowResult . Append ( ’PartType:
’+ I n t T o S t r ( Integer ( P a r t T y p e ) ) ) ;
61 Memo_ShowResult . Append ( ’Route: ’+ I n t T o S t r ( R o u t e ) ) ;
62 End ;
63 end ;
64

65 end .
code/exampleAppRecord.txt

2.0.1.3 Procedure

Declare a procedure that will be responsible for printing an instance of the type TOrder in a
MemoBox. Then, this procedure will have two arguments: TOrder and a TMemo.

2.0.1.4 Arguments by Value and by Reference

Update the procedure created in the last exercise. This new procedure should be able to print all
information and copy the ID of an instance TOrder to an argument. Then, this procedure will have
three arguments: TOrder, a TMemo and an integer variable.

2.0.1.5 Function and dynamic array

Develop an function that adds the ID members of two instances TOrder and returns the instance
TOrder with a lower Route destination. This function will have three arguments: two TOrder and
one integer.
Create other TButton to call this function. Moreover, you must implement a dynamic array of
TOrder that is incremented by a new order when the BT_AddOrder is pressed.
 Exercises on Free Pascal: Part 2 15

2.0.2 Implementation clues

The code below can assist you during the resolution of exercises presented in section 2.0.1.

1 u n i t Unit1 ;
2

3 {$mode objfpc}{$H+}
4

5 interface
6

7 uses
8 C l a s s e s , S y s U t i l s , Forms , C o n t r o l s , G r a p h i c s , D i a l o g s ,
StdCtrls ;
9

10 type
11 tRouter = 0 . . 7 ;
12 t P a r t T y p e = ( P a r t A = 0 , P a r t B , P a r t C , PartD , P a r t E ,
PartF , PartG ) ;
13

14 TOrder = record
15 id : integer ;
16 PartType : tPartType ;
17 Route : tRouter ;
18 end ;
19

20 t a r r a y _ o r d e r s = array of TOrder ;
21

22 { Ts }
23

24 Ts = c l a s s ( TForm )
25 BT_AddOrder : T B u t t o n ;
26 Bt_MinOrder : T B u t t o n ;
27 CB_PartType : TComboBox ;
28 C B _ D e s t i n a t i o n : TComboBox ;
29 Ed_Numb1 : T E d i t ;
30 Label_Numb1 : T L a b e l ;
31 Label_PartType : TLabel ;
32 L a b e l _ D e s t i n a t i o n : TLabel ;
33 L a b e l _ R e s u l t : TLabel ;
34 Memo_ShowResult : TMemo ;
 16 Exercises on Free Pascal: Part 2

35 procedure BT_AddOrderClick ( S e n d e r : T O b j e c t ) ;
36 procedure B t _ M i n O r d e r C l i c k ( S e n d e r : T O b j e c t ) ;
37 procedure F o r m C r e a t e ( S e n d e r : T O b j e c t ) ;
38 private
39

40 public
41 array_orders : tarray_orders ;
42 n u m b _ o r d e r s : integer ;
43 end ;
44

45 var
46 s : Ts ;
47

48

49

50 implementation
51

52 {$R *.lfm}
53

54 { Ts }
55

56 procedure Ts . F o r m C r e a t e ( S e n d e r : T O b j e c t ) ;
57 begin
58 numb_orders := 0;
59 end ;
60

61

62 procedure p r i n t O r d e r ( o r d e r : TOrder ; memo : TMemo) ;

63 begin
64 With o r d e r do
65 Begin
66 memo . C l e a r ;
67 memo . Append ( ’ID: ’+ I n t T o S t r ( i d ) ) ;
68 memo . Append ( ’PartType:
’+ I n t T o S t r ( Integer ( P a r t T y p e ) ) ) ;
69 memo . Append ( ’Route: ’+ I n t T o S t r ( R o u t e ) ) ;
70 End ;
71 end ;
72
 Exercises on Free Pascal: Part 2 17

73

74 procedure p r i n t O r d e r _ A n d C o p y ( o r d e r : TOrder ; memo : TMemo ;

var o u t _ i d : integer ) ;
75 begin
76 With o r d e r do
77 Begin
78 memo . C l e a r ;
79 memo . Append ( ’ID: ’+ I n t T o S t r ( i d ) ) ;
80 memo . Append ( ’PartType:
’+ I n t T o S t r ( Integer ( P a r t T y p e ) ) ) ;
81 memo . Append ( ’Route: ’+ I n t T o S t r ( R o u t e ) ) ;
82 out_id := id ;
83 End ;
84 end ;
85

86 function m i n R o u t e _ O r d e r ( orderA , o r d e r B : TOrder ; var

a d d V a l u e : integer ) : TOrder ;
87 begin
88 addValue := 0 ;
89 addValue := orderA . i d + orderB . i d ;
90 ShowMessage ( I n t T o S t r ( o r d e r A . i d ) + ’
’+ I n t T o S t r ( o r d e r B . i d ) + ’ r=’+ I n t T o S t r ( a d d V a l u e ) ) ;
91 if ( o r d e r A . R o u t e > o r d e r B . R o u t e ) then
92 begin
93 minRoute_Order := orderB ;
94 end
95 else begin
96 minRoute_Order := orderA ;
97 end
98 end ;
99

100 procedure Ts . BT_AddOrderClick ( S e n d e r : T O b j e c t ) ;

101 var
102 l o c a l O r d e r : TOrder ;
103 c_idx : integer = −1;
104 begin
105 Randomize ;
106 localOrder . id : = Random ( 1 0 0 0 ) ;
107 l o c a l O r d e r . P a r t T y p e : = t P a r t T y p e ( CB_PartType . I t e m I n d e x ) ;
 18 Exercises on Free Pascal: Part 2

108 l o c a l O r d e r . Route :=
StrToInt ( CB_Destination . Items [ CB_Destination . ItemIndex ] ) ;
109 / / p r i n t O r d e r _ A n d C o p y ( l o c a l O r d e r , Memo1 , c _ i d x ) ;
110 / / Memo_ShowResult . Append ( ’Variable received from
procedure:’ + I n t T o S t r ( c _ i d x ) ) ;
111

112

113 { Resize the length of the dynamic array }

114 SetLength ( a r r a y _ o r d e r s , numb_orders +1) ;
115 { Copy local variable to global variable }
116 a r r a y _ o r d e r s [ numb_orders ] := l o c a l O r d e r ;
117 { Show data }
118 p r i n t O r d e r ( a r r a y _ o r d e r s [ n u m b _ o r d e r s ] , Memo_ShowResult ) ;
119 { Increment number of elements in array }
120 i n c ( numb_orders ) ;
121 Memo_ShowResult . Append ( ’numbOrders:’ +
I n t T o S t r ( numb_orders ) ) ;
122 end ;
123

124 procedure Ts . B t _ M i n O r d e r C l i c k ( S e n d e r : T O b j e c t ) ;
125 var
126 addIDS : integer ;
127 a u x O r d e r : TOrder ;
128 begin
129 auxOrder := minRoute_Order ( a r r a y _ o r d e r s [ 0 ] ,
a r r a y _ o r d e r s [ 1 ] , addIDS ) ;
130 p r i n t O r d e r ( a u x O r d e r , Memo_ShowResult ) ;
131 Memo_ShowResult . Append ( ’Variable received from
function:’ + I n t T o S t r ( addIDS ) ) ;
132 end ;
133

134

135

136

137 end .

code/solutionsEx2.txt
Exercises on Free Pascal: Part 2 19

2.0.3 TTimers
Lazarus works with ”events”. For a procedure or function be capable of running with a specific
frequency, you must use a TTimer (that is available on the TAB ”System”). Please add one TTimer
and create the event onTimer that will present a ShowMessage with the text ”This is an event”.
Modify the property ”Interval” and analyze the change in the program behavior.
20 Exercises on Free Pascal: Part 2