Lesson 6
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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

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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

  • //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");

  • }

  • }


Simple Assignment

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 = x % 10

x += 10

x –= 10

x *= 10

x /= 10

x %= 10

Compound Assignment Equalities


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

  • 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


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;

}


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