Programming Methodology (1)

import java.util.*;

public class FindCost3{ public static void main(String[] args ) {

Scanner sc = new Scanner(System.in); double price, tax;

System.out.println("*** Product Price Check ***");System.out.print("Enter initial price: "); price = sc.nextDouble();

System.out.print("Enter tax rate: "); tax = sc.nextDouble();

price = price * (1 + tax/100); System.out.println("Cost after tax = " + price);

}}

RUN

*** Product Price Check ***Enter initial price: _1000

Enter tax rate: _12.5

Cost after tax = 1125.0

import java.util.*;

public class FindCost3{ public static void main(String[] args ) {

Scanner sc = new Scanner(System.in); double price, tax;

System.out.println("*** Product Price Check ***");System.out.print("Enter initial price: "); price = sc.nextDouble();

System.out.print("Enter tax rate: "); tax = sc.nextDouble();

price = price * (1 + tax/100); System.out.println("Cost after tax = " + price);

}}

Selection

Selection

Learning objectives

• explain the difference between sequence and selection;

• use an if statements to make a single choice in a program;

• use an if...else statement to make a choice between two options in a program;

• use nested if…else statements to make multiple choices in a program;

• use a switch statement to make multiple choices in a program.

Making choices

display the price of the seats requested ?

display a list of alternative flights ?

display a message saying that no flights are available to that destination ?

Selection in Java

if statement

if…else statement

switch statement

The ‘'if’' statement

if ( ){ }

// some code here

// some code here

// some code here

/* a test goes here */ question

The ‘'if’' statement: an example

if ( ){ }

temperature = sc.nextDouble();

System.out.println(“Below freezing”);

System.out.print(“Enter another temperature”);

temperature < 0

-5Below freezing

Enter another temperature

Enter another temperatureRUN12

Remember: you can have multiple instructions inside an if statement!

import java.util.*;public class FindCostWithDiscount{ public static void main(String[] args ) { double price, tax; Scanner sc = new Scanner(System.in); System.out.println("*** Product Price Check ***"); System.out.print("Enter initial price: "); price = sc.nextDouble(); System.out.print("Enter tax rate: "); tax = sc.nextDouble(); price = price * (1 + tax/100); System.out.println("Cost after tax = " + price); }}

// code to reduce tax here if price is greater than 100

if ( ){

}

price > 100

System.out.println (“Special promotion: Your tax will be halved!“); tax = tax * 0.5;

*** Product Price Check ***Enter initial price: 50

Enter tax rate: 10

Cost after tax = 55.0

*** Product Price Check ***Enter initial price: 1000

Enter tax rate: 10

Special Promotion: Your tax will be halved!

Cost after tax = 1050.0

The comparison operators of Java

Operator Meaning

== equal to

!= not equal to

< less than

> greater than

>= greater than or equal to

<= less than or equal to

if ( temperature >= 18 ){

System.out.println("Today is a hot day!");}

The comparison operators of Java

Operator Meaning

== equal to

!= not equal to

< less than

> greater than

>= greater than or equal to

<= less than or equal to

if (angle == 90){

System.out.println("This is a right angle!");}

The comparison operators of Java

Operator Meaning

== equal to

!= not equal to

< less than

> greater than

>= greater than or equal to

<= less than or equal to

if (angle != 90){

System.out.println("This is NOT a right angle!");}

The ‘'if…else’' statement

if (/* a test goes here */ ){ }

// some code here

// some code here

// some code here

// some code here

else{ }

The ‘'if…else’' statement

if ( ){ }

mark = sc.nextInt();

System.out.println("“You have passed!");

System.out.println("“You have failed!");

System.out.println("“Good luck with other exams");

else{ }

mark >= 50

import java.util.*; public class DisplayResult{ public static void main(String[ ] args) { int mark; Scanner sc = new Scanner(System.in);

System.out.println("What exam mark did you get? ");mark = sc.nextInt();if (mark >= 50){

System.out.println("Congratulations, you passed");}else{

System.out.println("I'm sorry, but you failed");}System.out.println("Good luck with your other exams");

}}

What exam mark did you get?

_

What exam mark did you get?

52Congratulations, you passedGood luck with your other exams

What exam mark did you get?

_

What exam mark did you get?

35Im sorry, but you failedGood luck with your other exams

Combining tests

5 Celsius TEMPERATURE 12 Celsius

if ( ) temperature >= 5 temperature <= 12&&

Logical operator Java counterpart

AND

OR

NOT

&&

||

!

if ( ) temperature >= 18! ( )

Nested ‘if…else’ statements

group time

A 10.00 a.m.

B 1.00 p.m.

C 11.00 a.m

if (group == 'A'){ }else {

}

if (group == 'B'){ }else {

}

if (group == 'C'){ }else{ }

System.out.print("No such group");

System.out.print("1.00 p.m");

System.out.print("11.00 a.m");

System.out.print("10.00 a.m");

if (group == 'A'){ }else {

}

if (group == 'B'){ }else {

}

if (group == 'C'){ }else{ }

System.out.print("No such group");

System.out.print("1.00 p.m");

System.out.print("11.00 a.m");

System.out.print("10.00 a.m");

if (group == 'A'){ System.out.print("10.00 a.m"); }else if (group == 'B'){ System.out.print("1.00 p.m"); }else if (group == 'C'){ System.out.print("11.00 a.m"); }else{ System.out.print("No such group"); }

The 'switch' statement

switch( )

{

}

someVariable

case value1: // instructions(s) to be executed

break;

case value2: // instructions(s) to be executed

break;

// more values to be tested can be added

default: // instruction(s) for default case

The 'switch' statement:

An example….

group time

A 10.00 a.m.

B 1.00 p.m.

C 11.00 a.m

switch( )

{

}

someVariable

case value1: // instructions(s) to be executed

break;

case value1: // instructions(s) to be executed

break;

// more values to be tested can be added

default: // instruction(s) for default case

group

‘A’: System.out.print("10.00 a.m");

‘B’: System.out.print("1.00 p.m");

case ‘C’: System.out.print("11.00 a.m"); break;

System.out.print(“No such group.");

switch( )

{

}

group

case ‘A’: System.out.print("10.00 a.m");

break;

case ‘B’: System.out.print("1.00 p.m");

break;

case ‘C’:

default: System.out.print(“No such group.");

System.out.print("11.00 a.m"); break;

10.00 a.m1.00 p.m11.00 a.mNo such group No such group11.00 a.m

Combining options

group time

A 10.00 a.m.

B 1.00 p.m.

C 11.00 a.m

Combining options

group time

A 10.00 a.m.

B 1.00 p.m.

C 10.00 a.m

switch(group)

{

case 'A': System.out.print("10.00 a.m ");

break;

case 'B': System.out.print("1.00 p.m ");

break; case ‘C’: System.out.print("10.00 a.m "); break;

default: System.out.print("No such group");

}

switch(group)

{

case 'A': System.out.print("10.00 a.m ");

break;

case ‘C’: System.out.print("10.00 a.m ");

break;

case 'B': System.out.print("1.00 p.m ");

break;

default: System.out.print("No such group");

}

switch(group)

{

case 'A': case ‘C’: System.out.print("10.00 a.m ");

break;

case 'B': System.out.print("1.00 p.m ");

break;

default: System.out.print("No such group");

}

import java.util.*;

public class SelectionQ4

{

public static void main(String[ ] args)

{

int x;

Scanner sc = new Scanner(System.in);

System.out.print("Enter a number: ");

x = sc.nextInt();

if (x > 10)

{

System.out.println("Green");

System.out.println("Blue");

}

System.out.println(“Red");

}

}

Enter a number: _

Red

10

import java.util.*;

public class SelectionQ4

{

public static void main(String[ ] args)

{

int x;

Scanner sc = new Scanner(System.in);

System.out.print("Enter a number: ");

x = sc.nextInt();

if (x > 10)

{

System.out.println("Green");

System.out.println("Blue");

}

System.out.println(“Red");

}

}

Enter a number: _

Green

20

Blue

Red

import java.util.*;

public class SelectionQ4

{

public static void main(String[ ] args)

{

int x;

Scanner sc = new Scanner(System.in);

System.out.print("Enter a number: ");

x = sc.nextInt();

if (x > 10)

{

System.out.println("Green");

System.out.println("Blue");

}

System.out.println(“Red");

}

}

Enter a number: _10

Blue

Red

import java.util.*;public class SelectionQ5{ public static void main (String[ ] args) { int x; Scanner sc = new Scanner(System.in); System.out.print("Enter a number: "); x = sc.nextInt(); if (x > 10) { System.out.println("Green"); } else {

System.out.println("Blue"); } System.out.println(“Red"); }}

Enter a number: _10

Blue

Red

import java.util.*;public class SelectionQ5{ public static void main (String[ ] args) { int x; Scanner sc = new Scanner(System.in); System.out.print("Enter a number: "); x = sc.nextInt(); if (x > 10) { System.out.println("Green"); } else {

System.out.println("Blue"); } System.out.println(“Red"); }}

Enter a number: _20

Green

Red

import java.util.*;

public class SelectionQ6

{

public static void main (String[ ] args)

{

int x;

Scanner sc = new Scanner(System.in);

System.out.print("Enter a number: ");

x = sc.nextInt();

switch (x)

{

case 1: case 2: System.out.println("Green"); break;

case 3: case 4: case 5: System.out.println("Blue"); break;

default: System.out.println("numbers 1-5 only");

}

System.out.println(“Red");

}

}

Enter a number: _1

Green

Red

import java.util.*;

public class SelectionQ6

{

public static void main (String[ ] args)

{

int x;

Scanner sc = new Scanner(System.in);

System.out.print("Enter a number: ");

x = sc.nextInt();

switch (x)

{

case 1: case 2: System.out.println("Green"); break;

case 3: case 4: case 5: System.out.println("Blue"); break;

default: System.out.println("numbers 1-5 only");

}

System.out.println(“Red");

}

}

Enter a number: _2

Green

Red

import java.util.*;

public class SelectionQ6

{

public static void main (String[ ] args)

{

int x;

Scanner sc = new Scanner(System.in);

System.out.print("Enter a number: ");

x = sc.nextInt();

switch (x)

{

case 1: case 2: System.out.println("Green"); break;

case 3: case 4: case 5: System.out.println("Blue"); break;

default: System.out.println("numbers 1-5 only");

}

System.out.println(“Red");

}

}

Enter a number: _3

Blue

Red

import java.util.*;

public class SelectionQ6

{

public static void main (String[ ] args)

{

int x;

Scanner sc = new Scanner(System.in);

System.out.print("Enter a number: ");

x = sc.nextInt();

switch (x)

{

case 1: case 2: System.out.println("Green"); break;

case 3: case 4: case 5: System.out.println("Blue"); break;

default: System.out.println("numbers 1-5 only");

}

System.out.println(“Red");

}

}

Enter a number: _10

numbers 1-5 only

Red

import java.util.*;

public class SelectionQ6

{

public static void main (String[ ] args)

{

int x;

Scanner sc = new Scanner(System.in);

System.out.print("Enter a number: ");

x = sc.nextInt();

switch (x)

{

case 1: case 2: System.out.println("Green"); break;

case 3: case 4: case 5: System.out.println("Blue"); break;

default: System.out.println("numbers 1-5 only");

}

System.out.println(“Red");

}

}

Enter a number: _10

Red

Design and implement a program that asks the user to enter two numbers and then guess at the sum of those two numbers. If the user guesses correctly a congratulatory message is displayed, otherwise a commiseration message is displayed along with the correct answer.

Enter first number_

Enter first number12

Enter second number_

Enter first number12

Enter second number6

Guess the sum_

Enter first number12

Enter second number6

Guess the sum18

Correct answer!

Enter first number_

Enter first number12

Enter second number_

Enter first number12

Enter second number6

Guess the sum_

Enter first number12

Enter second number6

Guess the sum14

Wrong answer!12 + 6 = 18