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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

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lesson 6

Lesson 6

Selection Structures

example program
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 operations
Simple Assignment

Compound Addition

Compound Subtraction

Compound Multiplication

Compound Division

Compound Remainder

=

+=

-=

*=

/=

%=

Compound Assignment Operations

(integers only)

compound assignment equalities
x = x + 10

x = x – 10

x = x * 10

x = x / 10

x = x % 10

x += 10

x –= 10

x *= 10

x /= 10

x %= 10

Compound Assignment Equalities
compound assignments
Compound 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
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
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
Round to two decimal places
  • (double) Math.round(answer*100)/100
math class1
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
Random Class
  • The Random class has two methods that will generate a random integer or double.
example of random class methods
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
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/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
  • 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
Syntax of the If Statement

if (test expression)

{

statement1;

statement2;

statementn;

}

//this is an example of a compound statement

if else 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
Syntax for if/else

if (test expression)

{

statement1;

statement2;

statementn;

}

else

{

statement1;

statement2;

statementn;

}

//example of compound statements

relational operators
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
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
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

\”

\’

\\

Backspace

Tab

Newline or line feed

Double Quote

Single Quote

Backslash

Escape Sequences
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