Lesson 6

Selection Structures

Example program• //This will convert a numeric grade into a letter grade• import TerminalIO.KeyboardReader;

• public class Grades• {• public static void main (String args [])• {• //Variables• double grade1,grade2, grade3, total;• //End of Variables•• //Input• KeyboardReader reader = new KeyboardReader();• System.out.print ("Please enter in the first grade: ");• grade1 = reader.readDouble();• System.out.print ("Please enter in the second grade: ");• grade2 = reader.readDouble();• System.out.print ("Please enter in the third grade: ");• grade3 = reader.readDouble();• //End of Input•• //Calculations• total = (grade1 + grade2 + grade3) / 3.0;• System.out.println ("The average is: "+total);• //End of Calculations•• //If Statements• if (total >= 94)• System.out.println ("The letter grade is: A");• if (total >= 84 && total <94)• System.out.println ("The letter grade is: B");• if (total >= 76 && total <84)• System.out.println ("The letter grade is: C");• if (total >= 68 && total <76)• System.out.println ("The letter grade is: D");• if (total <68)• System.out.println ("The letter grade is: F");• }• }

Compound Assignment OperationsSimple AssignmentCompound AdditionCompound

SubtractionCompound

MultiplicationCompound DivisionCompound Remainder

=+=-=*=/=%=

(integers only)

Compound Assignment Equalities

x = x + 10x = x – 10x = x * 10x = x / 10x = x % 10

x += 10x –= 10x *= 10x /= 10x %= 10

Compound Assignments

Translate the following statements to equivalent statements that use extended assignment operators:

a. X *=2 a. X = X *2;

b. Y = Y % 2; b. Y %= 2

Math Class

• The math class is quite extensive but we will concentrate a just a few of it’s properties:

static int abs(int x) Returns the absolute value of an integer x

static double abs (double x) Returns the absolute value of a double x

static double pow(double base, double exponent)

Returns the base raised to the exponent.

static long round (double x) Returns x rounded to the nearest whole number.

static int max (int a , int b) Returns the greater of a and b

static int min(int a , int b) Returns the lesser of a and b

static double sqrt (double x) Returns the square root of x.

Examples of Math Class Methods

int m;double x;

m = Math.abs(-7) // m equals 7x = Math.abs(-7.5) // x equals 7.5x = Math.pow(3.0,2.0) // x equals 3.0^2.0 = 9.0x = Math.pow(16.0, .25) // x equals 16.0 ^ .25 =

2.0m = Math.max(20,40) // m equals 40m = Math.min(20,40) // m equals 20m = (int) Math.round(4.27) // m equals 4

Round to two decimal places

• (double) Math.round(answer*100)/100

Math Class

//Given the area of a circle, compute its radius.

double area = 10.0, radius;radius = Math.sqrt(area / Math.PI);

Math.PI is accurate to about 17 decimal places

Random Class

• The Random class has two methods that will generate a random integer or double.

Method What is Doesint nextInt(int n) Returns a integer chosen at

random from among 0,1,2,3,…,n-1

double nextDouble() Returns a double chosen at random between 0.0 and 1.0, inclusive.

Example of Random Class Methods

Import java.util.Random;

Random generator = new Random();int i;double j;

i = generator.nextInt(3); // would give a // random number 0,1, or 2.

j = generator.nextDouble(); // would give a // random number // between 0 and 1

Control Structures

• A control structure is simply a pattern for controlling the flow of a program module.

• The three fundamental control structures of a structured programming language are sequence, selection, and iteration.

• Sequence control structure is what you have been doing up until now. The second two is what we are going to take a look at next.

Selection/Iteration Structure

• Selection and Iteration allow the flow of the program to be altered, depending on one or more conditions.

• Selection is implemented by using a if, if/else, and switch statements.

• Iteration is implemented by using the while, do/while, and for statements.

The IF statement

• The if statement works much the same as a if/then statement in Visual Basic.

• It uses relational operators to test if something is true or false.

• If it is true, the program will execute the statement(s) within the if statement.

• If it is false, the program will bypass the statements and continue with the statements following the if statement.

Syntax of the If Statement

if (test expression)

{

statement1;

statement2;

statementn;

}

//this is an example of a compound statement

IF/ELSE Statement

• The IF/ELSE statement works in the same manner as the if/then/else in Visual Basic.

• It is considered a double-alternative statement.

• If the expression evaluates as true, then the statements inside the if are executed.

• If the expression evaluates as false, then the statements inside the else are executed.

Syntax for if/else

if (test expression){

statement1;statement2;statementn;

}else{

statement1;statement2;statementn;

}//example of compound statements

Relational Operators

Relational operators allow two quantities to be compared.

= = Equal to

! = Not equal to

< Less than

< = Less than or equal

> Greater than

> = Greater than or equal

Logical Operators

Logical Operators

Switch Statement

• The switch statement works in the same manner as the case select statement in Visual Basic.

• A selector variable is first evaluated to produce a value.

• The selector is then compared to a series of cases.

• If the selector value matches one of the case values, the corresponding case statements are executed.

Syntax for a Switch Statement

switch (selector variable) //must be int or char{

case case1value : case1statements;break;

case case2value : case2statements;break;

case casenvalue : case_N_statements;break;

default : case exception statements;

}

Escape Sequences

\b\t\n\”\’\\

BackspaceTabNewline or line feedDouble QuoteSingle QuoteBackslash

Bottoms Up On The

Fourth Cup