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CSC 201
Lecture - 3
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Agenda
Review Lecture 2
Type Casting
Type Conversion Conditionals and Loops
In-Class Quiz Tuesday : Sep 8th
Next class : Book assignment will be givendue Tuesday Sep 8th.
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Review Of Lecture-2
Intro to Java.
Compiling/Executing Java programs
JDK, JRE, JVM Data Types, Variable, constants
Java program structure
Type Conversion - Introduction
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Errors
Every programming language has some set
of rules to be followed like Grammar in
English.
2 kinds of errors : Compile-time and
Runtime.
Compile-time error : Syntax errors.
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Java program structure
Consists of:
Variables
OperatorsExpressions, Statements and blocks
Control flow statements
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Variables
What is an identifier/variable?
Rules for writing/creating an identifier.
What happens if we give the foll.?int x = 10.0;
What if I write int x = 10;
(OR) int x;x = 10;
How to declare a float variable in Java?
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Operators
Arithmatic : +, -, *, /, %
Unary : +, -, ++, --, !
Boolean : Can have 2 values T or F. Conditional operators >=,
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Converting Strings to primitive
value for cmd line args
Rule: Whenever you use a + operator with
string as one of its operands, Java
automatically converts other to a string
produces string as a result.
Ex : string a = Hello;string b = csc;
string c = 201;
System.out.println(a + b + c);
What is the output?
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Expressions,Statements and
Blocks
Expression is made of variables, operatorsand methods.
Ex : int a = 0 (x+y)/100
Statements : Expressions can be madeinto statements by terminating with ;
Ex : a = a + 1;
System.out.println(Hi); Blocks : Group of zero or more statements
between balanced braces.
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Java Input and Output
Input : is any information that is needed by
your program to complete its execution.
Output : Any information that we get from
the computer.
Many ways to accept input from console.
One method : Scanner class. Java.util package contains some classes
for I/O.
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Example
import java.util.Scanner;
public class Scanning {
public static void main(String[] args) {
System.out.println("Enter a integer:"); Scanner myscan = new Scanner(System.in);
int i = myscan.nextInt();
System.out.println("Value of i is : " +i);
}
}
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Type Conversion
What is the importance of a data type?
Java is a strongly typed language.
Java is a statically typed language.
In Java : Explicit type conversion, Explicit cast. Difference between Typecast and Type
Conversion?
If you cast a variable into a string you are onlytemporarily considering it as a string.
Whereas with conversion you actually change itpermanently.
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Default Data type values
Byte = 0
Short = 0
Int = 0
Long = 0L Float = 0.0f
Double = 0.0d
Char = '\u0000 String (or any object) = null
Boolean = false
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Type conversion and Typecasting
Type conversion : Integer.parseInt()
Double.parseDouble()
Type Casting : Type conversion forprimitive types.
Ex: (int) 2.71 = 2
11 * (int) 0.3 = ?
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Java program structure
Consists of:
Variables
OperatorsExpressions, Statements and blocks
Control flow statementsDecision Making
Loop statements
Branching statements
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Booleans operators
Boolean type has 2 values : True or False
3 important bool operators : &&, ||, !
If we have 2 bool values a, b we can have following values
a && b is T ifBOTH operands are T
F ifEITHER operand is F
a || b is T ifEITHER operands are T
F ifBOTH operands are F
!a is T if a is F
F if a is T
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Comparison operators
==, != , =
These operators are defined for each primitive type and produce a booleanresult.
Ex : Results for below?
2 == 2
2 == 3
2 != 3
2 != 2
2 < 3
2 > 3
2 = 3If a and b are T, F
13) Calculate (!(a && b) && (a || b))
14) Calculate ((a && b) || !(a || b))
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Control Flow Statements
Decision making statements : If, If-else,switch
IF STATEMENT: If different action is to be
performed on different inputs, we use IFstatement. It is basically a decision makingstatement. Its construct is :
Form-1If ()
{ }
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Form 2 : if-else
If else statement
if()
{ ; }
else()
{ ; }
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Form-3 : Nested If else
if()
;
else
if() { ; }
else
if() { ; }
..
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Example If else
Class test
{
Public static void main(String[] args)
{
int x = 2;
if(x < 5){
System.out.println( Number is less than 5.);
}
else
System.out.println(Number is greater than or equal to 5.);}
}
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Nested If-else
int score;
char grade;
Scanner scan = new Scanner(System.in);
score = scan.netInt();
if(score >= 80)
grade = A;else
if(score >= 70)
grade = B;
else
if(score >= 60)grade = C
System.out.println(Grade is : +grade); o/p : Correct
More than one statementis satisfied here!
But once a condn is satisfied,
Remaining are not evaluated.
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int score;
char grade;
Scanner scan = new Scanner(System.in);
score = scan.nextInt();
if(score >= 80)
grade = A;else
if(score >= 70)
grade = B;
else
if(score >= 60)grade = C
System.out.println(Grade is : +grade); O/P = ?
Remove!
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Switch statement
It is a shortcut to certain form of if-statement. If we have a stack of if
statements, Java has a shorthand i.e
switch-case statements.if (x == 0) dosomething();
else if (x == 1) dosomethingelse();
else if(x == 2) dosomethingelse();
..
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Syntax for switch statement
Switch (x) //x must be variable/expression
{
Case 0: dosomething(); break;
Case 1: dosomethingelse(); break;Case 2: dosomethingelse(); break;
..
Case n: dosomethingelse(); break;Default : dosomethingelse();
}
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switch(x) : x must be a variable or an expression that canbe cast to an int without loss of precision.
Differences between if-else and switch
An if-else can be used to make decisions on range ofvalues or conditions.
A switch statement can make decisions only on integervalues.
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Switch Example
Class switch_demo
{
public static void main(String[] args)
{
int x;
System.out.println(Enter a number between 1 and 3 inclusive:);
Scanner s = new Scanner(System.in);x = s.nextInt();
switch(x)
{
case 1: System.out.println(You printed A); break;
case 2: System.out.println(You printed B); break;
case 3: System.out.println(You printed C); break;
default: System.out.println(No letter is chosen);}
}
}// we can also write the same using the If else loop.
Importance of
Break?
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Looping Statements
There are 3 basic forms of looping: while,
for, do statements.
While loop:
Syntax
while ( )
{ }The statements get executed until the
boolean expression evaluates to False.
The bool expression must
evaluate to T for the
Statements to execute
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While loop example
int a = 0;
while( a
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Example
Class whiledemo
{
public static void main(String[] args)
{
int count = 1;while(count < 11)
{
System.out.println(Count is : + count);
count++;}
}
}
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Do-While Loop
Do-while statement: Same as While statement. Theexpression is evaluated at the bottom instead of top. So,loop will run atleast once.
int count = 1;
do{
System.out.println(Count is: + count);
count++;
}while(count < 11);}
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For Loop
If you want to initialize one or more variables
and may want to increment one or more
variable. The loop is repeatedly executed until a
particular condition is satisfied.Syntax:
For (initialization ; boolean-exp ; increment)
{set of statements
}If the expression evaluates to
false., the loop is
terminated
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Example
Class for_demo
{
public static void main(String[] args)
{
for(int I = 1; I < 11; i++)
{
System.out.println(Count is : +i);
}
}
}
How to create an infinite loop with for?
Invoked after eachIteration of the loop!
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Branching Statements
Break statement : If in some scenario you
want to exit the loop without completing
the rest of the execution of statements
Break was used in our switch statement.
Continue statement : A continue statement
returns to the beginning of the innermost
enclosing loop w/o completing the rest ofthe statements of the loop.
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Continue statement example
Public static void main(String[] args){
int num;
for(num = 1; num < 15; num++)
{
if(num >= 9){ System.out.println(The number +num+ is greater than or
equal to 9!);}
else
continue;
System.out.println(This statement executes:);}
}//what is the output here?
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Infinite Loops
What is an infinite loop?
while(true)
{ }
for(; ; )
{} //infinite loop
May be used in embedded control code which some may be designedto run forever.
Sometimes used, when you dont know the exact condition under whichyou want to use a while, but you can break the loop by using breakas of its statements in the body.
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Program to check if a number is
prime or notpublic static void main(String[] args){
int num_to_check, mod, I;
System.out.println(Enter a number to check if it is prime or not:);
//check using scanner class
for(I = 2; i< num_to_check ; i++)
{ mod = num_to_check % i;
if(mod == 0)
{
System.out.println(Not a prime number);
break;
}
}if(I == num_to_check)
System.out.println(Prime Number!);
}
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Announcements
Homework 1 is due Thursday. It is posted
on my blog.
There will an In-class quiz on Tuesday
Sep8th 2009.
The prime number example will be posted
with comments.
Next lab session.
Exam timings : 12:15 12:45
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Homework output sample run
A random number generated is : 2
Enter the limit for printing even numbers : 5
The number 1 is not an even number
The number 2 is an even nummber
The number 2 matches the random number 2
The number 3 is not an even number
The number 4 is an even number
The number 5 is not an even number
