02. Data Types and variables

Numeral Types, Text Types and Type Conversion
Data Types and Variables
Software University
http://softuni.bg
SoftUni Team
Technical Trainers

Table of Contents
1. Data Types and Variables
2. Integer and Real Number Type
3. Type Conversion
4. Boolean Type
5. Character and String Type
2

sli.do
#tech-fund
Have a Question?
3

 Computers are machines that process data
 Instructions and data are stored in the computer
memory
How Computing Works?
5
10110

 Variables have name, data type and value
 Assignment is done by the operator "="
 Example of variable definition and assignment
 When processed, data is stored back into variables
Variables
6
int count = 5;Data type
Variable name
Variable value

 A data type:
 Is a domain of values of similar characteristics
 Defines the type of information stored in the computer
memory (in a variable)
 Examples:
 Positive integers: 1, 2, 3, …
 Alphabetical characters: a, b, c, …
 Days of week: Monday, Tuesday, …
What Is a Data Type?
7

 A data type has:
 Name (Java keyword)
 Size (how much memory is used)
 Default value
 Example:
 Integer numbers
 Name: int
 Size: 32 bits (4 bytes)
 Default value: 0
Data Type Characteristics
8
int: sequence of 32 bits in
the memory
int: 4 sequential bytes in
the memory

 Always refer to the naming conventions
of a programming language for Java use camelCase
 Preferred form: [Noun] or [Adjective] + [Noun]
 Should explain the purpose of the variable
(Always ask yourself "What this variable contains?")
Naming Variables
9
firstName, report, config, usersList, fontSize
foo, bar, p, p1, populate, LastName, last_name

 Scope == where you can access a variable (global, local)
 Lifetime == how long a variable stays in memory
Variable Scope and Lifetime
10
String outer = "I'm inside the Main()";
for (int i = 0; i < 10; i++) {
String inner = "I'm inside the loop";
}
System.out.println(outer);
// System.out.println(inner); Error
Accessible in the main()
Accessible only in the loop

 Variable span is how long before a variable is called
 Always declare a variable
as late as possible (e.g. shorter span)
static void main(String[] args) {
String outer = "I'm inside the main()";
for (int i = 0; i < 10; i++)
//System.out.println(inner); Error
}
Variable Span
11
"outer"
variable span

 Shorter span simplifies the code
 Improves its readability and maintainability
for (int i = 0; i < 10; i++) {
}
String outer = "I'm inside the main()";
// System.out.println(inner); Error
Keep Variable Span Short
12
"outer" variable
span – reduced

14
Type
Default
Value
Min Value Max Value Size
byte 0 -128 (-27) 127 (27-1) 8 bit
short 0 -32768 (-215) 32767 (215 - 1) 16 bit
int 0 -2147483648 (-231) 2147483647 (231 – 1) 32 bit
long 0
-9223372036854775808
(-263)
9223372036854775807
(263-1)
64 bit
Integer types

 Depending on the unit of measure we can use different data types:
Centuries – Example
15
byte centuries = 20;
short years = 2000;
int days = 730484;
long hours = 17531616;
System.out.printf(
"%d centuries = %d years = %d days = %d hours.",
centuries, years, days, hours)
//20 centuries = 2000 years = 730484 days = 17531616 hours.

 Integers have range (minimal and maximal value)
 Integers could overflow  this leads to incorrect values
Beware of Integer Overflow!
16
byte counter = 0;
for (int i = 0; i < 130; i++) {
counter++;
System.out.println(counter);
}
1
2
…
127
-128
-127

 Examples of integer literals:
 The '0x' and '0X' prefixes mean a hexadecimal value
 E.g. 0xFE, 0xA8F1, 0xFFFFFFFF
 The 'l' and 'L' suffixes mean a long
 E.g. 9876543L, 0L
Integer Literals
17
int hexa = 0xFFFFFFFF; //-1
long number = 1L; //1

 Read four integers
 Add first to the second
 Divide the sum by the third number (integer division)
 Multiply it by the fourth number
 Print the result
Problem: Integer Operations
18
10
20
3
3
30
20
30
2
3
75
15
14
2
3
42

int firstNumber = Integer.parseInt(sc.nextLine());
int secondNumber = Integer.parseInt(sc.nextLine());
int thirdNumber = Integer.parseInt(sc.nextLine());
int fourthNumber = Integer.parseInt(sc.nextLine());
long result = firstNumber + secondNumber;
result = result / thirdNumber;
result = result * fourthNumber;
System.out.println(result);
Solution: Integer Operations
19
Check your solution here: https://judge.softuni.bg/Contests/1227/

 Floating-point types:
 Represent real numbers, e.g. 1.25, -0.38
 Have range and precision depending
on the memory used
 Sometimes behave abnormally in the calculations
 May hold very small and very big values like
0.00000000000001 and
10000000000000000000000000000000000.0
What are Floating-Point Types?
21

 Floating-point types are:
 float (±1.5 × 10−45 to ±3.4 × 1038)
 32-bits, precision of 7 digits
 double (±5.0 × 10−324 to ±1.7 × 10308)
 64-bits, precision of 15-16 digits
 The default value of floating-point types:
 Is 0.0F for the float type
 Is 0.0D for the double type
Floating-Point Numbers
22

 Difference in precision when using float and double:
 NOTE: The "f" suffix in the first statement!
 Real numbers are by default interpreted as double
 One should explicitly convert them to float
float floatPI = 3.141592653589793238f;
double doublePI = 3.141592653589793238;
System.out.println("Float PI is: " + floatPI);
System.out.println("Double PI is: " + doublePI);
PI Precision – Example
23
3. 1415927
3. 141592653589793

 Write program to enter a radius r (real number) and prints the
area of the circle with exactly 12 digits after the decimal point:
 Sample solution:
Problem: Circle Area (12 Digits Precision)
24
2.5 19.634954084936 1.2 4.523893421169
double r = Double.parseDouble(sc.nextLine());
double area = Math.PI * r * r;
System.out.printf("%.12f", area);

 Floating-point numbers can use scientific notation, e.g.
 1e+34, 1E34, 20e-3, 1e-12, -6.02e28
Scientific Notation
25
double d = 10000000000000000000000000000000000.0;
System.out.println(d); // 1.0E34
double d2 = 20e-3;
System.out.println(d2); // 0.02
double d3 = Double.MAX_VALUE;
System.out.println(d3); //1.7976931348623157E308

 Integral division and floating-point division are different:
Floating-Point Division
26
System.out.println(10 / 4); // 2 (integral division)
System.out.println(10 / 4.0); // 2.5 (real division)
System.out.println(10 / 0.0); // Infinity
System.out.println(-10 / 0.0); // -Infinity
System.out.println(0 / 0.0); // NaN (not a number)
System.out.println(8 % 2.5); // 0.5 (3 * 2.5 + 0.5 = 8)
System.out.println(10 / 0); // ArithmeticException

 Sometimes floating-point numbers work incorrectly!
 Read more about IEE 754
Floating-Point Calculations – Abnormalities
27
double a = 1.0f;
double b = 0.33f;
double sum = 1.33d;
System.out.printf("a+b=%f sum=%f equal=%b",
a+b, sum, (a + b == sum));
// a+b=1.33000001311302 sum=1.33 equal = false
double num = 0;
for (int i = 0; i < 10000; i++) num += 0.0001;
System.out.println(num); // 0.9999999999999062

BigDecimal
 Built-in Java Class
 Provides arithmetic operations
 Allows calculations with very high precision
 Used for financial calculations
28
BigDecimal number = new BigDecimal(0);
number = number.add(BigDecimal.valueOf(2.5));
number = number.subract(BigDecimal.valueOf(1.5));
number = number.multiply(BigDecimal.valueOf(2));
number = number.divide(BigDecimal.valueOf(2));

 Write program to enter n numbers and print their exact sum:
Problem: Exact Sum of Real Numbers
29
2
1000000000000000000
5
1000000000000000005
2
0.00000000003
333333333333.3
333333333333.30000000003

Solution: Exact Sum of Real Numbers
30
int n = Integer.parseInt(sc.nextLine());
BigDecimal sum = new BigDecimal(0);
for (int i = 0; i < n; i++) {
BigDecimal number = new BigDecimal(sc.nextLine());
sum = sum.add(number);
}
System.out.println(sum);

Live Exercises
Integer and Real Numbers

 Variables hold values of certain type
 Type can be changed (converted) to another type
 Implicit type conversion (lossless): variable of bigger type
(e.g. double) takes smaller value (e.g. float)
 Explicit type conversion (lossy) – when precision can be lost:
Type Conversion
33
Implicit conversion
Explicit conversion
float heightInMeters = 1.74f;
double maxHeight = heightInMeters;
double size = 3.14;
int intSize = (int) size;

 Calculate how many courses will be needed to elevate n persons by
using an elevator of capacity of p persons.
 Sample solution:
Problem: Elevator
34Check your solution here: https://judge.softuni.bg/Contests/1227/
persons = 17
capacity = 3
6
int p = Integer.parseInt(sc.nextLine());
int courses = (int) Math.ceil((double)n / p);
System.out.println(courses);

 Write program to enter an integer number of centuries and
convert it to years, days, hours and minutes
Problem: Centuries to Minutes
35
The output is
on one row
1
1 centuries = 100 years = 36524 days =
876576 hours = 52594560 minutes
5 centuries = 500 years = 182621 days
= 4382904 hours = 262974240 minutes
5

Solution: Centuries to Minutes
36
int centuries = Integer.parseInt(sc.nextLine());
int years = centuries * 100;
int days = (int) (years * 365.2422);
int hours = 24 * days;
int minutes = 60 * hours;
System.out.printf(
"%d centuries = %d years = %d days = %d hours = %d minutes",
centuries, years, days, hours, minutes);
(int) converts
double to int
Tropical year has
365.2422 days

 Boolean variables (boolean) hold true or false:
Boolean Type
38
int a = 1;
int b = 2;
boolean greaterAB = (a > b);
System.out.println(greaterAB); // False
boolean equalA1 = (a == 1);
System.out.println(equalA1); // True

 A number is special when its sum of digits is 5, 7 or 11
 For all numbers 1…n print the number and if it is special
Problem: Special Numbers
39
20
1 -> false
2 -> false
3 -> false
4 -> false
5 -> true
6 -> false
7 -> true
8 -> false
9 -> false
10 -> false
11 -> false
12 -> false
13 -> false
14 -> true
15 -> false
16 -> true
17 -> false
18 -> false
19 -> false
20 -> false

Solution: Special Numbers
40
for (int num = 1; num <= n; num++) {
int sumOfDigits = 0;
int digits = num;
while (digits > 0) {
sumOfDigits += digits % 10;
digits = digits / 10;
}
// TODO: check whether the sum is special
}

 The character data type
 Represents symbolic information
 Is declared by the char keyword
 Gives each symbol a corresponding integer code
 Has a '0' default value
 Takes 16 bits of memory (from U+0000 to U+FFFF)
 Holds a single Unicode character (or part of character)
The Character Data Type
42

 Each character has an unique Unicode value (int):
Characters and Codes
43
char ch = 'a';
System.out.printf("The code of '%c' is: %d%n", ch, (int) ch);
ch = 'b';
ch = 'A';
ch = 'щ'; // Cyrillic letter 'sht'

 Write a program to read an integer n and print all triples of the first
n small Latin letters, ordered alphabetically:
Problem: Triples of Latin Letters
44
3
aaa
aab
aac
aba
abb
abc
aca
acb
acc
baa
bab
bac
bba
bbb
bbc
bca
bcb
bcc
caa
cab
cac
cba
cbb
cbc
cca
ccb
ccc

Solution: Triples of Latin Letters
45
for (int i = 0; i < n; i++)
for (int j = 0; j < n; j++)
for (int k = 0; k < n; k++) {
char letter1 = (char)('a' + i);
char letter2 = // TODO: finish this
char letter3 = // TODO: finish this
System.out.printf("%c%c%c%n",
letter1, letter2, letter3);
}

 Escaping sequences are:
 Represent a special character like ', " or n (new line)
 Represent system characters (like the [TAB] character t)
 Commonly used escaping sequences are:
 '  for single quote "  for double quote
  for backslash n  for new line
 uXXXX  for denoting any other Unicode symbol
Escaping Characters
46

Character Literals – Example
47
char symbol = 'a'; // An ordinary character
symbol = 'u006F'; // Unicode character code in a
// hexadecimal format (letter 'o')
symbol = 'u8449'; // 葉 (Leaf in Traditional Chinese)
symbol = '''; // Assigning the single quote character
symbol = ''; // Assigning the backslash character
symbol = 'n'; // Assigning new line character
symbol = 't'; // Assigning TAB character
symbol = "a"; // Incorrect: use single quotes!

String
Sequence of letters
48
"ABC"

The String Data Type
 The string data type
 Represents a sequence of characters
 Is declared by the String keyword
 Has a default value null (no value)
 Strings are enclosed in quotes:
 Strings can be concatenated
 Using the + operator
49
String s = "Hello, JAVA";

 Strings are enclosed in quotes "":
 Format strings insert variable values by pattern:
Formatting Strings
50
String file = "C:Windowswin.ini";
The backslash is
escaped by
String firstName = "Svetlin";
String lastName = "Nakov";
String fullName = String.format(
"%s %s", firstName, lastName);

 Combining the names of a person to obtain the full name:
 We can concatenate strings and numbers by the + operator:
Saying Hello – Examples
51
String firstName = "Ivan";
String lastName = "Ivanov";
String fullName = String.format(
"%s %s", firstName, lastName);
System.out.printf("Your full name is %s.", fullName);
int age = 21;
System.out.println("Hello, I am " + age + " years old");

 Read first and last name and delimiter
 Print the first and last name joined by the delimiter
Problem: Concat Names
52
John
Smith
->
John->Smith
Linda
Terry
=>
Linda=>Terry
Jan
White
<->
Jan<->White
Lee
Lewis
---
Lee---Lewis

String firstName = sc.nextLine();
String lastName = sc.nextLine();
String delimiter = sc.nextLine();
String result = firstName + delimiter + lastName;
System.out.println(result);
Solution: Concat Names
53
Jan<->White

 …
 …
 …
Summary
55
 Variables – store data
 Numeral types:
 Represent numbers
 Have specific ranges for every type
 String and text types:
 Represent text
 Sequences of Unicode characters
 Type conversion: implicit and explicit

 https://softuni.bg/courses/technology-fundamentals

SoftUni Organizational Partners

 Software University – High-Quality Education and
Employment Opportunities
 softuni.bg
 Software University Foundation
 http://softuni.foundation/
 Software University @ Facebook
 facebook.com/SoftwareUniversity
 Software University Forums
 forum.softuni.bg
Trainings @ Software University (SoftUni)

 This course (slides, examples, demos, videos, homework, etc.)
is licensed under the "Creative Commons Attribution-NonCom
mercial-ShareAlike 4.0 International" license
License
60

02. Data Types and variables

More Related Content

What's hot

Similar to 02. Data Types and variables

More from Intro C# Book

Recently uploaded

02. Data Types and variables

Editor's Notes