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### Lesson 6

### Bottoms Up On The

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 Addition

Compound Subtraction

Compound Multiplication

Compound Division

Compound Remainder

=

+=

-=

*=

/=

%=

Compound Assignment Operations(integers only)

x = x – 10

x = x * 10

x = x / 10

x = x % 10

x += 10

x –= 10

x *= 10

x /= 10

x %= 10

Compound Assignment EqualitiesCompound Assignments

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

a. X = X *2;

a. X *=2

b. Y %= 2

b. Y = Y % 2;

Math Class

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

Examples of Math Class Methods

int m;

double x;

m = Math.abs(-7) // m equals 7

x = Math.abs(-7.5) // x equals 7.5

x = Math.pow(3.0,2.0) // x equals 3.0^2.0 = 9.0

x = Math.pow(16.0, .25) // x equals 16.0 ^ .25 = 2.0

m = Math.max(20,40) // m equals 40

m = Math.min(20,40) // m equals 20

m = (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.

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

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;

}

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