java_lect_03-2.ppt

JAVA-NLP Lecture series
Variables, Expressions and
Arithmetic Operators in JAVA
Lecture #3
manish@cse.iitb.ac.in

Variables
 A variables can be considered as a name given
to the location in memory where values are
stored.
 One syntax of variable declaration
dataType variableName;
 Do you imagine that the variable can change its
value – yes, that is why it is called as variable.
 Is the following variable name is legal:
GrandTotal ? Suggest good name for it?

Variable Names and Keywords
 Use only the characters 'a' through 'z', 'A' through 'Z', '0'
through '9', character '_', and character '$'. A name can’t
contain space character.
 Do not start with a digit. A name can be of any length.
 Upper and lower case count as different characters.
So SUM and Sum are different names.
 A name can not be a reserved word.
 A name must not already be in use in this part of the
program.
 A reserved word is a word which has a predefined
meaning in Java. For example int, double, true, and
import are reserved words.

Questions on Variable Names
 int good-bye;
 int shrift = 0;
 char thisMustBeTooLong;
 int bubble = 0,toil = 9, trouble = 8
 int 8ball;
 int double;

Answers
 int good-bye; //bad variable name
 int shrift = 0; //OK
 char thisMustBeTooLong; //OK in syntax
//but poor choice in variable name
 int bubble = 0,toil = 9, trouble = 8
// “;” missing at the end
 int 8ball; //can’t start with a digit
 int double; //double is a reserve word

Expressions
 An expression is a combination of constants
(like 100), operators ( like +), variables(section
of memory) and parentheses ( like “(” and “)” )
used to calculate a value.
 x = 1; y = 100 + x;
 This is the stuff that you know from algebra, like:
(32 - y) / (x + 5)
 There are rules for this, but best rule is that
an expression must look OK as algebra.
 Based on what you know about algebra, what is
the value of 12 - 4/2 + 2 ?
 Spaces don’t much matter.

Arithmetic Operators
 What is the value of –12 + 3
 An arithmetic operator is a symbol that
asks for doing some arithmetic.
Operator Meaning Precedence
- Unary minus highest
+ Unary Plus highest
* Multiplication middle
/ Division middle
% Modulus middle
+ addition low
- Subtraction low

basicOperation.java
class basicOperation {
//arithmetic using variables
public static void main() {
int a = 1+ 1;
int b = 3 * 3;
int c = 1 + 8/ 4;
int d = -2;
System.out.println( “a = ” + a);
System.out.println(“b = ” + b);
System.out.println(“c = ” + c);
System.out.println(“d = ” + d);
}
}

basicMath.java
class basicMath {
//arithmetic using variables
public static void main() {
int a = 1+ 3;
int b = a * 3;
int c = b / 4;
int d = c – a;
int e = -d;
System.out.println( “a = ” + a);
System.out.println(“b = ” + b);
System.out.println(“c = ” + c);
System.out.println(“d = ” + d);
System.out.println(“e = ” + e);
}
}

Parentheses
 Difference between -1 * ( 9 - 2 ) * 3 and -1 * 9 - 2 * 3
 To say exactly what numbers go with each operator, use
parentheses.
 Nested Parentheses: The expression is evaluated starting
at the most deeply nested set of parentheses (the
"innermost set"), and then working outward until there
are no parentheses left. If there are several sets of
parentheses at the same level, they are evaluated left to
right.
 ( ( ( 32 - 16 ) / ( 2 * 2 ) ) - ( 4 - 8 ) ) + 7
 Are arithmetic expressions the only kind of
expression?

intergerDivision.java
class integerDivision {
public static void main ( String[] args ) {
System.out.println("The result is: " + (1/2 +
1/2) );
}
}
 What is the value of 99/100 ?
 Change print statement to “print” (1.0/2 + 1/ 2 .0)

final reserve word
class calculateTax {
public static void main ( String[] arg ) {
l final char c = ‘A’; f
final int count = 0;
. . . . . .
}
}

Assignment No.1
 Write a program that averages the synsets created
for three months April, May and June. Declare and
initialize variable to the synset entered for each
month. Compute the average and write out the
results, something like this:
Synsets Entered for April: 12
Synsets Entered for May : 14
Synsets Entered for June: 8
Average Synset Entered: 11.333333
Check that your program prints the correct results.

Assignment No. 2
 Write a program that computes summation of 1 to n
numbers where n can be any positive number.
Declare and initialize variables and print the output
as
Value of n is : 5
Sum of first 5 positive numbers : 15
Check the correctness of the result.

java_lect_03-2.ppt

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