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IT guys in this video we're going to take a look at if statements if else statements and comparison

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operators so if statements are used to evaluate some kind of condition and then do something based on

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that condition or something else.

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If that condition isn't met.

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All right so the syntax is very simple and much like just about every other programming language at

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least every C syntax language.

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Basically we have.

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If something is true then we're going to do something else then we're going to do something else.

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All right.

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So that's the basic simple syntax right.

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So it's comment that because it's not actual code.

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So what I'm going to do is create a variable called ID and I'm going to set it to 100.

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So we're going to first look at the equal comparison operators so let's say cool too.

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So what we'll do is we'll put an if statement here and we're going to say if Id meaning that variable

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we just created is equal to 100.

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All right.

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Now this double equal sign means that we're comparing this to this.

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It's not an assignment operator like the single equal sign.

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All right.

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So make sure that you don't get these to confuse this is assignment.

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OK we're assigning 100 to ID.

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Here we're comparing 100 to ID.

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So if this is true then let's just go ahead and console Lague and we'll just log correct.

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All right.

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So if we go ahead and save this and run it down here you'll see.

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Correct.

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OK.

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If I go ahead and change this to let's say if ID is equal to 1 a 1 and save then nothing happens.

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And that's that's what should happen because we didn't define any else.

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So if we wanted to define an else we would just go like this and we would say console Daut log and let's

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just say incorrect and save and now we get incorrect because ID does not equal 101 it equals 100 if

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I were to change just two on a one and save then we'll get correct.

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All right.

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I'm just going to undo that.

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Now at the same time we can also do not equal two.

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So we go down here let's say not equal to.

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And I'm actually just going to copy this and paste to then.

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Now not equal is going to be an exclamation and then an equal sign.

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So this is basically saying if ID is not equal to 101 an ID is actually set to 100 so it is not equal

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to 1 0 1.

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So we should get correct here.

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So if I save you can see the second one here we get correct.

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All right.

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Now this way is basically just testing the value.

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OK it's not testing the type.

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If I were to let's actually change this back to 100 if I were to change this ID right here to a string

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of 100 and then keep this ID equals 100 and save which we get correct.

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All right.

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Because it doesn't matter in this case it doesn't matter if this is a string or a number.

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It's still 100.

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Now this isn't really the way that you want to do it.

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Most times most times you want to test the value and the type is it.

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It stops a lot of different errors in issues from arising.

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So that's what I would suggest and what most programmers would suggest and the way that you do that

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is to use three equal signs.

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All right so what we'll do is we'll copy this let's say equal to the value and type and then what we'll

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do is just add an extra equal sign here.

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Now we have a string of 100 and then we're testing this.

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Three equals two the number 100.

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So if we save this and we check out the last one here it's incorrect because this is a number.

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This is a string.

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So if we change this back to a number by removing the quotes and then we save.

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Now we get correct.

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All right.

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So to avoid issues I would suggest using this most of the time.

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All right.

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At least when in doubt.

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Now we can also do not equal to the value and the type.

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So if we copy this and what we can do is just change the first one to an exclamation and then keep the

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double equals.

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So if we save that we get incorrect.

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And the reason for that is because ID is in fact not the right value and the right type.

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All right.

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If I were to change this back to a string that's now not going to be equal to the 100 number.

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So if I save now we get correct.

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All right.

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So just keep that in mind you want to.

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You want to by default used to triple equals OK.

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And this here.

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So what do we need to do now is just common all this out because I don't want all these logs over here.

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And then I want to test to see if this is actually define this ID.

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So you may think that we would do something like this.

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So if Id then consul dot log will just say no ID or I'm sorry we'll log the ID.

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So I'll put this inside of a template string so I'll use back ticks and will say the ID is and then

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we can put a variable like this.

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We already went over the template strings or template literals else.

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Then let's cancel dot log.

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No ID.

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All right.

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So if I go out and save this it's going to say the idea is 100 which is fine.

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But if we were to take this out of here so that there is no ID define and save we're going to get an

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error that says ID is not defined even though all we're doing is testing it here.

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It's still going to give us this error.

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So the correct way to test this would be is to use the type of operator and test to see if it's undefined.

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So remember the type of type of if type of ID is not equal to undefined.

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Then we want to log the ID else then we'll say no ID so let's save that.

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When I do this should be an issue actually should be in quotes.

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All right so now we get no ID.

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So if you want to test to see if something is undefined to see if it's not there at all then you want

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to use this.

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OK you don't want to just say if ID because you're going to get an error you want to test the type and

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see if it's equal to or not equal to undefined.

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You could do it either way you could say equal to undefined and then have this here and this here or

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you could do it this way.

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All right let's put a comment here.

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We'll just say test if undefined.

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All right.

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So I'm going to go ahead and just uncomment the idea up here and we'll go ahead and comment.

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So all right so so far we've gone over equal to not equal to in both.

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Also using the value in the type also testing to see if something's undefined.

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So now let's test if something is greater than or less than right.

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So we'll see a greater or less than I'm sure a lot of you guys already know this stuff is pretty easy.

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So what I'll do is copy this I will say if I d Let's do it Friday is greater than 200

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words.

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Well just keep correct and incorrect.

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All right.

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So if I go ahead and save that we get incorrect because obviously ideas set to 100 which is not greater

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than 200.

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If I were to change id to 300 and save we get correct.

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So very very easy.

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We can also put an equal sign here because right now even if I say one hundred and save we get incorrect.

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If we want to test to see if it's 100 or greater we can do greater than or equal to and then we save

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and we get correct.

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All right so greater than or equal to.

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And then you can also do of course less than or equal to I'm not going to retype it because this is

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very easy stuff and I don't want to take up too much time here.

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All right so it's going comment that out now we're going to take a look at if.

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Else.

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OK.

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So basically what I'm going to do here is I'm going to set a variable let's call it color and we'll

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set it to a string of yellow.

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All right.

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And then we're going to do is put in F here and I'm going to say if color is equal to red I should set

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it to read first so save it's equal to red then let's console log.

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Color is red.

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All right.

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And then instead of doing just else like we did above we can test other conditions by saying else if

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and then another condition.

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All right so what we'll do here is we'll say if color is equal to blue

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then we'll Konsole dot log

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color is blue.

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OK.

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Now if I save this we're going to get color is red.

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OK if I change it to blue will get color is blue.

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Now if I change it to yellow we get nothing.

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So this is where we can put in an else.

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All right.

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And we can keep doing other else if we could say if you know color is orange or whatever.

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But when you want to actually end it all just to an else and to go ahead we'll do console log and we'll

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say color is not red or blue K needs to be something that makes sense.

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So we have yellow in here we run through the tests the owls see the Yousif and it's not it doesn't match.

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So we get color is not red or blue.

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All right so now I want to do is take a look at logical operators.

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All right so if we want to test to see if we want to test more than one thing we can use these operators

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so let's create a name.

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Let's say Steve and let's create an age

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we'll say age equals 20.

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OK.

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And then what we'll do is we'll do an if statement and we're going to say if the age is greater than

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zero and a double ampersand which represents and age is less than 12.

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All right so if that's true then we want to console Daut logs.

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We want to cancel dot log and we're going to say the name.

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OK so the name variable actually will put a template string in here make it easier.

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So put a variable like this name is a name is a child.

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OK.

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And then we'll do LCF or CHRONICAN.

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We're kind of combining the logical operators and the else have here.

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So say Alsip age is greater than or equal to 13.

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And age is less than or equal to 19.

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OK if that's the case then we're going to say console log throw a template string in here and we'll

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say

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say name is a teenager.

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OK.

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And then let's do Pells

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console dot log

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back to X..

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I keep doing that name is an adult.

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All right.

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So let's go ahead and save that and we get Steve as an adult because we have Steve at 20 years old if

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we change him to 15 and say we get Steve as a teenager if we change him to four.

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We get Steve as a child.

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All right.

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So the ampersand the end logical operator is going to make sure that this and this are both true.

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OK both of them not just one but both.

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Now we want to make sure just one is true then we could use or.

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All right.

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So let me actually put a comment here so this is.

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And which is represented with two ampersands.

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OK we also have or which is represented with two pipe characters.

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All right.

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So what I'm going to do here is say if

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you will say if age is less then 16 or age is greater than let's say 65 then we're going to say Konsole

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doth Lague

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and we'll say name we'll say this is a race registration so cannot run in race.

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All right.

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So basically we have if we have a race and we have some kind of program to evaluate people that are

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allowed to run in it we can't have people that are under 16 or over 65 running in the race.

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All right so that would be a case you would use or so we'll say else console dog log will say the name

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is registered for the race.

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All right.

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So something like that and Steve cannot run in the race because he's four years old and four year olds

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cannot run in the race.

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Let's go ahead and put them at let's say twenty five and save.

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And now he's registered for the race.

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We put him at 70 save.

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You might have a heart attack so he can't run in the race.

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All right.

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So these are all the basics.

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Now I do want to show you a couple of shorthand ways of doing conditionals so the ternary operator is

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something that is available in most programming language languages.

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So as a tertiary operator and this is just a very shorthand way of doing conditionals.

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So what we'll do here is we'll do a console dot log.

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All right.

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And we're going to go back to using the ID that we have here which is set to 100.

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So we want to basically output our console log.

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Correct.

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If it's equal to 100 and incorrect if it's not.

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So we can do that by simply saying ID equals or is equal to 100.

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And then the turnaround operator which is a question mark.

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All right.

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So if this is true then we want to output correct.

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Now the else is represented with a colon.

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So we want to output incorrect.

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All right.

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So this is much shorter than writing out you know a full statement in logging correct and incorrect

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like we did above.

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So it's going save that we get incorrect.

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Why do we get incorrect.

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Consul log ID is equal to 100.

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That's because I have it as a string.

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We use the triple equals So let's save that.

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And now we get correct.

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All right.

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So you can see that this is much easier and I mean you know I can use this in every situation and every

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if statement but for something like this just makes it much easier.

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All right.

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Another thing that I want to mention is that in javascript when you do an if statement the brackets

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are the curly braces are actually optional.

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They are recommended I would suggest using them but it will work without them.

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So let's say without question capitalizes.

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So I will say without braces.

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So if we were to say if an ID is equal to one hundred and notice I'm not going to put the curly braces

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here I'm just going to go down to the next line and indent and do a console log.

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Correct.

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And then I'll do one else.

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So go like that and say Konsole dot log.

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And correct and save.

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And we get correct.

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All right so this is possible but again I wouldn't suggest it.

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I would suggest sticking with the curly braces.

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All right guys so that is it for if statements and if else statements and the next video we're going

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to jump into switches which is another form of a conditional and Javascript.