major topic 2 - condition

8/13/2019 Major Topic 2 - Condition

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My program is smarter than

a 5

th

grader!By: Chelsea Celestino

PROVE IT!


2/29

We have learned about variables, expressions, getting aninput and display an output! Weve been computing a lot of

things this past week right?

So far

I can do thattoo! Pssh,

youre not sospecial!

Mr. Calculator

.

INTRPRG AY 2011-2012 1st Term


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4/29

We need to make our programs think and make a DECISION!

Bring out your wands and say ----- No, no, not that.

We need to make them a bit smarter!

Step

1

INPUT

Statement1

Statement2

Our program needs to be

able to do different thingsbased on an input!

Example :If Jim got the right answer he gets 1 point.

Ifthe file isnt there, display an error

message.



5/29

They are able to perform a CHECK (by doing a test). Theycheck if a certain condition is TRUE or NOT

Thankfully, computers do have some

sense in them!

When Java performs a CHECK,there are only two possible answers:pass or fail TRUEorFALSE.



6/29

To figure out if Jim got the correct answer, weshould know the correct answer . We should

also know what Jims answer was so we canprobably say something like:

1. Are two things equal?

2. Is something greater than another?

3. Is something less than another?

How does Java check?

Write your conditions in a way Java can understand!

If Jims answer

is equal to correct answer



7/29

Whats the difference between the two?

Two plus three is five. STATEMENT

Is two plus three five? QUESTION

Lesson 1 Formulating your conditionIf Jims answer is equalto correct answer

Whats up with that?

X = 2 + 3

if (X == 2 + 3)

=

Not Equal To

Greater than

Greater thanor equal to

Less than

Less than orequal to



8/29

Pay attention to the syntax!Look at where your semi-colonshould be placed!

Try the following code:

Flex your fingers


Sample Input:

23 and 32,

100 and 50,

0 and 0,

-23, -27


9/29

Lets look at the anatomy:Enter: if Statement

boolean expression

Sequence ofstatements to executeif the condition is true


Or The End?End the program

Move on?with the remainingstatements?


10/29

What if we remove the elsethen? How is it different?

Open GuessTheNumber.java

Remember our guessing game?


Do this if conditionis true!

But if NOT, do thisinstead! (ONLY do this if

condition is FALSE)

Do this REGARDLESSif the condition is true

or not!!

Enter: ELSE


11/29

if (x < y)

int t = x;

x = y;

y = t;

System.out.println (Done!);

You mean like this?


Can I have more than one statement

under an ifor an else?

But, HOW do you tell Java which lines to

include under an if statement?


12/29

Lets say the user inputs 15 for both x and y.Any difference?

Is the curly braces always required?

Try the two codes below:


Defining a block of code

if (x < y)

x = x + 5;

y = y 5;

System.out.println(x + + y);

if (x < y){

x = x + 5;

y = y 5;

}

System.out.println(x + + y);

Yhasavalueof10infirstcodewhileithasavalueof15inthesecondcode!


13/29

What if all else fails?!

No problem, Java can handle that!


What if I want to execute my elsebased

only on a certain condition also?

if (grade >= 15)

System.out.println(Awesome!);

else if (grade >= 10)

System.out.println(Pretty good!);

else if (grade >= 5)

System.out.println(What happened!);

else

System.out.println(Dont worry

about it!);

Simply add an else

at the end!


14/29

She means this one:


How is that different from having several

ifsinstead? Whats thebig diff

huh?

if (grade >= 15)

System.out.println(Awesome!);

if (grade >= 10)

System.out.println(Pretty good!);

if (grade >= 5)

System.out.println(What

happened!);


15/29

Input Output using Else If Output using Many Ifs

8 What happened? What happened?

14 Pretty Good Pretty Good

What happened?17 Awesome Awesome

Pretty GoodWhat happened?

Think it doesnt matter?

Think again.


The mystery of Else Ifs and Many Ifs

Now, think some more.What really happened just now?

Dont want!My brainstired!


16/29

What really is happening


How Java interprets the two codes

if (grade >= 15)

if (grade >= 10)

if (grade >= 5)

if (grade >= 15)

else If (grade >=

10)

if (grade >= 5)

This is read only if the first if is

FALSE

This is read only if the

SECOND if is FALSE

Next!

Next!

Multiple ifs are checked one by one!

Else ifs are checked depending on the result

of the previous condition


17/29

Okay, imagine theres a promo in a store where the customer

has to choose a color (ROYGBIV) and a number (099). Theprize is as follows:

If both color and number is correct, customer gets 1 Million Pesos!

If only color or number is correct, customer gets 1K Pesos!

Lets create a program to simulate this!

1. We have to know what is the correct color and number. (Orangeand

23)

2. Next, we have to get the customers guess!3. Then we perform a check and display the result!


Lets check what we know so far


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int numGuess = in.nextInt();String colGuess = in.next();

if (numGuess == 23)

System.out.println (Numbers correct!);if (colGuess.equalsIgnoreCase(orange))

System.out.println (Colors correct!);

System.out.println

(You win 1 million pesos!);

Okay, lets try one solution first


Testing testing


19/29

Number is correct and color is wrong

but the user still won 1 million pesos!

Lets examine the output:


Mhm.. Not quite.

This time theyre BOTH wrong!

but still the user wins 1 mill!?

Color is correct but number is wrong ---

STILL WHAT THE @#$#@ ?!

Yourescheming tomake mebankrupt?


20/29

Okay, lets try using an else then!


Dont forget your curly braces!

if (numGuess == 23)System.out.println (Numbers correct!);

elseif (colGuess.equalsIgnoreCase(orange))

{

System.out.println (Colors correct!);System.out.println

(You win 1 million pesos!);

}

And else here anda couple of thosecurly braces should

do the trick!


21/29

Lets check the output of that code


Some more Tests

Oh theres an improvement! but it

didnt display the 1k Prize hmm.

Would be nice if it told us to try

again next time huh?

Oh no, have to hide this output from

boss yikes!

We need the numberAND color to be

BOTH correctbefore we give the 1

mill prize...


22/29

Lets see how


Java can combine conditions!

if (numGuess == 23)

if (colGuess.equalsIgnoreCase(Orange))System.out.println(Congratulations!);

else

System.out.println(You win 1k Pesos!);

Hey! Why no statement after if ?A: An if is still a statement so this is valid!


23/29

Whats wrong this time?

When number is wrongand color is correct, no message on

the 1k Prize! Cheat!


Still problematic

Lets look a little closer shall we?

if (numGuess == 23)

if (colGuess.equalsIgnoreCase(Orange))

Check for thesecond condition if

andONLY IF thefirst condition isTRUE

Arrgh!


24/29

Meet your logical operators!


AND

OR

also known as &&

also known as | |

IF you wantALLof your conditions to be true

IF you wantANYof your conditions to be true


25/29

Okay, try out this code.


Enter: AND / OR

if (numGuess == 23 ||

colGuess.equalsIgnoreCase(Orange))

if (numGuess == 23 &&

colGuess.equalsIgnoreCase(Orange))System.out.println(1 million Pesos!);

else

System.out.println(1k Pesos!);

elseSystem.out.println(Try again!);


26/29

*Drum Roll*


OH MY!

FINALLY!ITS PERFECTLY

WORKING!

... We forgot one more operator though...


27/29

The last tool in your condition box is the NOT operator!


The Loner:

NOTalso known as !

I like to negateothers! Thats just

how I am!

Use this whenyou dont know the values you want but

know the values you DONT WANT.

Th NOT t h f


28/29

if (!(x < 9))


The NOT operator can rephrase some of

your conditions

if (x >= 9)same as

if (!x == true) if (x == false)same as

if (!(x < 9)&& y


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The End!

major topic 2 - condition

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