INFORMATION & COMPUTER SCIENCE DEPARTMENT, KFUPM

ICS102, SECTIONS 52, 54 & 55  (001 Semester)

INTRODUCTION TO COMPUTING

LAB  #02 Primitive Types & Arithmetic Expressions

 

Instructor: Bashir M. Ghandi

 

Objectives:

To gain experience with:

• primitive data types in java
• defining and initialising variables
• writing arithmetic expressions
• changing the values of variables through assignment
• appreciating the importance of comments and good code layout
• using the TextIO class for Console Input

 

1.  Primitive data types

Java has very many data types built into it, and you (as a programmer) can create as many more as you want. However, all data in Java falls into one of two categories: primitive data and objects. There are only the eight primitive data types. Any data type you invent will be a type of object. 

Much more will be said about objects in the future (since Java is a object oriented programming language.) The following will be all you need to know, for now:

• A primitive data value uses a small, fixed number of bytes.
• There are only eight primitive data types.
• A programmer can not create new primitive data types..
• An object is a big block of data. An object may use many bytes of memory.
• An object usually consists of many internal pieces.
• The data type of an object is called its class.

A (crude) analogy is that a primitive data value is like a nut or a bolt, but an object is like a whole machine.

Integer Primitive Data Types
Type	Size	Range
byte	8 bits	-128 to +127
short	16 bits	-32,768 to +32,767
int	32 bits	(about)-2 billion to +2 billion
long	64 bits	(about)-10E18 to +10E18

Floating Point Primitive Data Types
Type	Size	Range
float	32 bits	-3.4E+38 to +3.4E+38
double	64 bits	-1.7E+308 to 1.7E+308

 

 

 

 

Other Primitive Data Types
char	32 bits	Unicode character set
boolean	8 bits	true  & false

 

 

 

 

If you just type a whole number, e.g: 125, Java will automatically represent it as type int.  If you want it represented as type long, you must follow the number with “L” as in, 125L.  (You can also use small letter l, but that can be confused with the number 1 “one”).  You can do similar thing with byte and short.

The default representation for floating point numbers is double.  If you specifically wish to request for a float, you must append your number with f or F. e.g. 12.5f

2.  Declaring and Using Variables.

Variables are used to store data values in the memory for a program to process.  You can use any of the above primitive types to declare variables.  (You can also declare variables of a particular class.  In that case, they are called objects).

A variable declaration is a request to the system to allocate memory for data values to be stored.  It involves specifying the type and a name for the variable.  The type is used by the system to know how many bytes of memory to allocate and the name is used by the programmer to refer to the allocated memory.

e.g.     int age;          int numberOfStudents;          double average;

 

If we have an initial value to assign to your variables, you can do so at initialization as follows:

int numberOfStudents = 25;

                        

 

3.  Arithmetic Operators

Arithmetic operators are used to form arithmetic expressions.  If several operators are used in an expression, there is a specific order in which the operations are done. Operators of higher precedence will operate first. There are many operators in Java, the following shows just a few:

In the table, operators in the same group have equal precedence. So, for example, plus ("+") and minus ("-") have the same precedence.

Note:  The operators give different result depending on the type of the operands. E.g.

20.0 – 12.0 / 10.0 = 20.0 – 1.2 = 18.8

20 – 12 / 10 = 20 –1 = 19

 

4.  Assignment Statement:

Variables are called so because we can change their values any number of times within a program.  One way of assigning or changing the value of a variable is using the assignment statement.   The assignment statement has the form:

variable = expression;

 

the expression can be a literal value (e.g. 25), another variable, or an expression involving both literals and variables.  E.g.

int first, second;

double average;

first = 10;

second = 20;

average = (first+second)/2.0

 

If a data value is not going to change in a program, it is declared to be a constant using the final keyword.  Constants are conventionally  declared using capital letters.  E.g.

final double PI = 3.1415;

5.  The Math class

Many mathematical functions and constants are included in the Java library.  They are included in the Math class.  some of these functions are shown below:

.

E :  The double value that is closer than any other to e, the base of the natural logarithms.

PI  The double value that is closer than any other to pi

abs(a)           Returns the absolute value of a                a can be double, float, int or long.

cos(double a)           Returns the trigonometric cosine of an angle in radians.

exp(double a)    Returns the exponential number e (i.e., 2.718...) raised to the power of a double value.

log(double a)      Returns the natural logarithm (base e) of a double value.

max(a, b)      Returns the greater of two values        a and b can double, float, int or long.

min(a, b)      Returns the smaller of two values        a and b can double, float, int or long..

pow(double a, double b)   Returns value of the first argument raised to the power of the second.

random()  Returns a double value with a positive sign, greater than or equal to 0.0 and less than 1.0.

round(a)     Returns the closest long to the argument             the argument can be double or float.

sin(double a)         Returns the trigonometric sine of an angle in radians.

sqrt(double a)       Returns the correctly rounded positive square root of a double value.

tan(double a)        Returns the trigonometric tangent of an angle in radians.

toDegrees(double angrad)   Converts an angle in radians to the equivalent angle in degrees.

toRadians(double angdeg)   Converts an angle in degrees to the equivalent angle in radians.

 

To access any of these methods, we need to prefix it with the name of the class, Math.  e.g

 

root = Math.sqrt(20.0);

 

6.  Console Input

 

Reading input from the console (text mode) is a bit complex for beginners to Java. To avoid this complexity, we shall initially be using a class, TextIO, which has been designed to simplify console input operations.

 

The TextIO class has the following methods which are used to read the desired type of input.

 readByte()            :   reads a byte from the data source.

 readChar()           :   reads a character.

 readDouble()        :   reads a double

 readFloat()           :   reads a floate.

 readInt()               :   reads an integer.

 readLong()           :   reads a long integer.

 readShort()          :   reads a short integer.

 readString()        :   reads a string made out of non-white space

 

To use the TextIO class, you need to add the following pieces of code to your programs:

• Import the TextIO class by placing the following import statement at the beginning of your program:

            import TextIO;

 

• Create a TextIO object as a field inside your class:

                                static TextIO stdin = new TextIO(System.in);

                Note: The parmeter to TextIO can be keyboard (System.in), a data file or a URL

 

• Change the heading of the main method as follows:

     public static void main(String[] args) throws java.io.IOException;

 

For all these to work, you need to copy the file TextIO.class to the same folder containing your program.

You can get the TextIO.class from my home page by right clicking the previous link.  You can also copy it from my machine (icswww).

 

7.  Examples:

Example 1:

The following program reads two int values from the user and prints the following

·         Their sum

·         Their difference

·         Their product

·         Their average

·         Their distance (absolute difference)

·         Their Maximum

·         Their Minimum

 

import TextIO;

 

/*  Reads two integer numbers from the user and prints the result

    of applying various arithmetic operations with them

*/   

 

public class Arithmetic {

     

      static TextIO stdin = new TextIO(System.in);

 

      public static void main(String[] args) throws java.io.IOException {

           

            int num1,num2; //two variables to be used for reading input

           

            System.out.print("Enter First integer number: ");

            num1=stdin.readInt();

            System.out.print("Enter Second integer number: ");   

            num2=stdin.readInt();

           

            System.out.println("The sum is: " + (num1+num2));

            System.out.println("The difference is: " + (num1-num2));

            System.out.println("The product is: " + (num1*num2));

            System.out.println("The average is: " + ((num1+num2)/2.0));

            System.out.println("The distance is: " + Math.abs(num1-num2));

            System.out.println("The maximum is: " + Math.max(num1,num2));

            System.out.println("The minimum is: " + Math.min(num1,num2));

      }

}

 

 

Comments.

The message between /* … */ is called comments.  It is ignored by the compiler.  It is a good practice to always explain the purpose of a program using comments.

Any message following // to the end of a line is also regarded as a comment.  This is usually used to explain the meaning of variables. 

 

You are expected to write comments explaining each program you write in this course.  You are also expected to comment any variable whose purpose is not obvious.

 

Layout.

Notice how the statements inside a class and those inside a method are indented using tabs.  This makes programs very easy to read.  You are equally expected to use good layout in writing your programs.

 

Example2:

The following program reads the sizes of a rectangle and prints:

·         The Area of the rectangle

·         The Perimeter of the rectangle

·         The Diagonal of the rectangle.

 

import TextIO;

 

/*  Reads the sides of a rectangle and prints

    the area, circomference and diagonal

*/

 

public class Rectangle {

 

      static TextIO stdin = new TextIO(System.in);

     

      public static void main(String[] args) throws java.io.IOException {

     

            double length,breadth;

           

            System.out.print("Enter the lenght of the rectangle: ");

            length=stdin.readDouble();

            System.out.print("Now enter the breadth: ");

            breadth=stdin.readDouble();

           

            System.out.println("The area is : "+ (length*breadth));

            System.out.println("The perimeter is : "+ (2*(length+breadth)));

            System.out.println("The diagonal is : "+ Math.sqrt(length*length+breadth*breadth));

      }

}

 

8.  Assignments

1.        Copy and paste each of the above programs into a JCreator, or get them from my computer (icswww), compile and test run them.  Make sure you understand what is going on in each of them.

 

2.        Write a program that reads temperature in Fahrenheit and prints the equivalent temperature in centigrade. 

centigrade = 5/9(fahrenheit-32)

 

Sample Run:

    3.        Write a program that prompts the user for a radius and prints:

·         The area of a circle of that radius                                      pr²

·         The circumference of a circle of that radius                     2pr

·         The volume of a sphere of that radius                              4/3 pr³

·         The surface area of a sphere of that radius                     4pr²

 

Sample Run:

 

4.        Write a program that reads two times in 24 hours format and prints the difference between the two times in hours and minutes.  You can assume that the second time is later than the first.

 

Sample Run:

 

9.  Home Work

1      Write a program that asks the following user input:

·         The number of gallons of gas in the tank of a car

·         The fuel efficiency in miles per gallon

·         The price of gas per gallon

The program then prints

·         How far (in miles) the car can travel with the gas

·         The cost of the travelling 100 miles with the car.

 

2.        Write a program that direct a Cashier of a super market on how to give change.  The program has two inputs:

·         The amount due

·         The amount received

Your program should give the minimum number of Riyal notes and coins possible.  You can assume that the amount due is not more than SR500 and that it is always less than or equal to the amount received.  Assume that the following Riyal notes and coins are available:

200 Riyals note

100 Riyals note

50 Riyals note

10 Riyals note

5 Riyals note

1 Riyals note

50 halala coin

25 halala coin

10 halala coin

5 halala coin

1 halala coin