Java Tutorial
Part 4: Data and
Calculations

Variables
Storing and
Processing Data
in the Memory

 Computers are machines that process data
 Both program instructions and data are stored in
the computer memory
 Data is stored by using variables
How Does Computing Work?
10110

 A variable is a container for information
 A named area of the computer memory
 The data can be read and changed at any time
 Variables provide means for:
 Storing data
 Retrieving the stored data
 Modifying the stored data
Variables

 Variables are characterized by:
 name (identifier)
 type (of the data preserved)
 value (stored information)
 Defining a variable in Java:
Variables
int age = 25;
Data
type
Variable
name
Variable
value
Name Type Value
age int 25
name String "Peter"
size double 3.50
Computer memory

Data Types
Text, Numbers,
and Other
Types in Java

 Variables store value of a certain type
 Number, letter, text (string), date, color, picture, list, …
 Data types:
 int – an integer: 1, 2, 3…
 double – a floating-point number: -0.5, 3.14, …
 boolean – a boolean: true, false
 char – a symbol: 'a', 'b', '#', …
 String – text: "Hello", "World", …
Data Types

 Data types define ranges of values with similar
characteristics
 Data types are characterized by:
 Name
 Example: boolean, int, String
 Size (memory usage)
 Example: 4 bytes
 Default value
 Example: 0
Data Types (2)

Statements
Commands in the
Computer Programs

 The actions that a program takes, are expressed as statements
 Common statements (actions / commands) include:
 Declaring a variable
 Assigning a value
 Declaring + initializing
Statements
int counter;
counter = 1;
int counter = 1;
 Printing a value
System.out.println(counter);
 Modifying a value
counter++;
sum = a + b;

 If-else statement
 Method definition statement
Complex Statements
if (a == 5)
System.out.println("Five");
else
System.out.println("Not Five");
 Loop statement
int a = 5;
while (a > 0) {
a--;
}
static int sum(int a, int b) {
return a + b;
}

Arithmetic Operators
Add, Subtract, Multiply
and Divide Numbers
+ -
* /

 Adding numbers (operator + )
 Subtracting numbers (operator - )
Arithmetic Operators: + and -
int a = 5;
int b = 7;
int sum = a + b;
System.out.println(sum); // 12
int a = 15;
int b = 7;
System.out.println(a - b); // 8

 Multiplying numbers (operator *)
 Dividing numbers (operator / )
Arithmetic Operators: * and /
int a = 5;
int b = 7;
System.out.println(a * b); // 35
int a = 25;
int b = 4;
System.out.println(a / b); // 6

 When dividing integers, the result is also integer:
 When dividing floating-points, the result is also floating-point:
Division Behavior in Java
int a = 25;
System.out.println(a / 4); // Integer result: 6
System.out.println(a / 0); // Error: division by 0
double a = 15;
System.out.println(a / 2.0); // 7.5
System.out.println(a / 0.0); // Infinity
System.out.println(0 / 0.0); // NaN

 Modulo / remainder from integer division (operator % )
Arithmetic Operators: %
int a = 7;
int b = 2;
System.out.println(a % b); // 1
System.out.println(3 % 2); // 1
System.out.println(4 % 2); // 0
System.out.println(3.5 % 1); // 0.5
7 = 3 * 2 + remainder 1
3 = 1 * 2 + remainder 1
4 = 3 * 2 + remainder 0
3.5 = 3 * 1 +
remainder 0.5

Expressions
Calculations with
Values and Operators
(a+b)
*c -1

 Expressions == sequences of operators, literals and
variables which are evaluated to a value
 Consist of at least one operand
 Can have 1 or more operators
Expressions
int r = (150-20) / 2 + 5;
int y = x + 5;
String name = "John Doe";

 Write a program to convert from USD to EUR:
 Read a floating-point number: the dollars to be converted
 Convert dollars to euro (use fixed rate of dollars to euro: 0.88)
 Print the converted value in euro formatted to the 2nd digit
Problem: Currency Converter
17 14.96
87 76.56
Judge: https://judge.softuni.org/Contests/Practice/Index/3253

Creating a New Project in IntelliJ IDEA

Solution: Currency Converter
Scanner scanner = new Scanner(System.in);
double dollars = scanner.nextDouble();
double euros = dollars * 0.88;
System.out.printf("%.2f", euros);

Submission in the Judge System
https://judge.softuni.org/Contests/Practice/Index/3253

 Write a program, which:
 Reads 2 real numbers from the console
 Performs 4 arithmetic operations on the obtained
2 numbers, in the following order: +, -, *, /
 Formats and prints the results like this example:
Problem: Four Operations
5
10
5.00 + 10.00 = 15.00
5.00 - 10.00 = -5.00
5.00 * 10.00 = 50.00
5.00 / 10.00 = 0.50

Solution: Four Operations
double num1 = Double.parseDouble(sc.nextLine());
double num2 = Double.parseDouble(sc.nextLine());
double sum = num1 + num2;
System.out.printf("%.2f + %.2f = %.2fn",
num1, num2, sum);
// TODO: Implement the rest of operations
Denotes a
new line

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