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Hello this is mortars or Curdy.



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And in this material we're going to create an idea of function or Mfat named as operator is tapped so



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that whenever the user taps on the operator something happens you're going to see the results here.



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Let's go inside this head here later class and after the increase the price of this number is to have



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to function we're going to say private void and the name is going to be operator is that operator is



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typed and then put up or Apprentice's.



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So we are ready to create a parameter for this function because we want to pass the operator that is



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actually tapped to this function whenever.



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Each move it or any a function or a switch statement calls this function or method we are going to pass



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the operator that is papped to that this method.



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So are going to say operator and the name is going to be tapped operators tapped.



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Operator And we're going to open and close this method by using these curly braces and first of all



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if you are great you are going to create an if statement inside this operator is tapetum it.



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So we're going to say if current operator current operator is not equal to non.



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And then we're going to often enclose these statements by using these curly braces.



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There isn't that we created this if statement is that.



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So for example in the emulator for example there is nothing here and the user actually presses on this



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plus OPERATOR We don't want anything to happen because the current operator is not.



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OK so in that case we are creating an if statement we are saying that if the current operator is not



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non OK and we are going to create another if statement if we can actually create an and logical operator



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here so we have.



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If current operator is not equal to not an current number that number is not equal to an empty string.



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So this means that there is something there is a number on this screen on the text view.



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And we want to actually do some operation on it.



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So first we are saying that if the current operator is not equal to not and the current number is not



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equal to an empty string then we can go inside each statement and say strange number.



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That's right assignment operator current number current numbers semicolon.



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So here we are saying that the number is that is actually at the right hand side of the operator is



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going to be the kind of number so if you are assigning the column number to the string number that's



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right.



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So let me show you the emulator.



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So let me show you this calculator.



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And here for example we have number five.



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Number five is the current operator and we press and this multiplication operator and we press on the



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number six.



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So number six is the current operator right.



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And we also want this number six.



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There is actually at the right hand side of this the multiplication operator to be the current number.



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So you're saying the current number that is actually the number 6 it is the string number at.



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Right.



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OK.



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So that's why we are assigning the current number to this three number.



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That's right.



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Valuable because this is how it is actually implemented.



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A little unclear but and again let me show you let me explain again.



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We have numbers too.



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This is the number at left and it is also the kind of number.



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And we press on.



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For example the plus operator.



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Now I want to press on the number three.



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Number three is the current number right.



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So it is also going to be the number at the right hand side of the operator of the plus operator.



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So if you're saying that the current number to be to be assigned to this Thring number.



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Right.



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OK.



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So that's how it is implemented.



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So now that the current number is assigned to this thing number asteroid we are going to say Carne's



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number assignment operator two quotes.



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So now we're going to empty this current number valuable because the value of the current number is



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already assigned to the string number.



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That's right.



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Valuable.



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We don't need it anymore.



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We are going to we we're going to actually empty this valuable this current number variable so that



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we can actually do something else with it later.



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Let's go back to our function this method.



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Operator restaffed Meffert.



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Now to create a switch statement here in order to switch between the values of the current operator.



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So we're going to say switch.



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And here I want to just put current.



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Operator here kind of later.



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Open and close this.



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So is this meant by using these curly braces.



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So we already provided our limited values for the operator for the current operator because the current



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operator is of type operator that we created ourselves inside our class so we can say case and then



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we have the value plus case.



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If the current operator if the value of the current operator is Plus break.



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So let me show you the emulator we have.



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Let me.



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We have this subtract operator case.



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If the value of the current operator is subtract



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call it break and if the value of the current operator is for example multiplication operators so case



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multiply break.



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And we have this why the divide operator chase the right break.



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And finally we have this equal operator so here we see a case



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case



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equal colon break.



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OK.



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So now for now I don't want you to just think about this equal operator and how these functions.



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This actually did it in this case equal.



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And for now I'm going to talk more about this later.



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For now let's just focus on the main operators the plus operator subtract multiply and divide operators.



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So now what happens when they use their taps.



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On the plus operator Let's see the created of a variable of type integer named as calculations resolved.



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It is of typing teacher assignment operator.



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So if we're going to say in teacher the class teacher that parse in and we need to pass a string value



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to this method parse it in order to convert it to an integer value.



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So if we have three number that's left plus.



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So let me create an inline integer integer that parse the pars and string number at.



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Right.



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You're going to add the value of the string number at lift to the value that is actually at the right



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hand side of the operator string number at right and the result is going to be assigned to these calculations



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result variable h.



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We have this break statement now.



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Let's see what happens.



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And to use a pass on the subtract operator here we are going to see calculations result.



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Assignment operator in teacher and teacher but parts in it.



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String number lift's string Ratliffe minus integer the parse and



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integer that parse gained string number.



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That's right.



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So three numbered right semicolon.



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So break.



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Now let's see what happens when the user taps on the multiplication operator.



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So again tabulation is resolved.



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Assignment operator teacher.



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That part's amed three numbers.



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Lift multiply.



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Buy in teacher that parts end string number.



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That's right.



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Semicolon.



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And finally we have this device OPERATOR So the calculation is resolved.



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Assignment operator integer that parse ain't string number.



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Lift divided by integer the parts in string number.



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That's right.



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String number three semicolon.



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So now after the ending curly brace of this sweet statement here I'm going to say that string number



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at lift strange number adds lift.



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Assignment operator streambed dot value of calculations result calculations result semicolon.



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So if you were to convert the calculations result to a string value and we're going to assign it to



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this three number at left roudy able.



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Why.



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Let me show you why.



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Let me show you the emulator.



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So now here it is our emulator right.



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And here for example we have number five.



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Number five multiplied by two.



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OK.



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And now I am going to for example say plus as you can see the multiply the number five multiplied by



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two the result is 10 right.



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So we have number 10 here and here you can see it at.



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Take a look at these takes you here at the top it is 10 plus.



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When he said Number Five multiplied by two.



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I didn't present this equal in here.



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I pressed on this plus.



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Operator.



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So the number five multiplied by two operation is executed and the result which is going to be number



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10 is assigned to this three number that's left Raddy bet.



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Now the result which is is number 10 is at the left hand side of this plus.



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Operator OK now number 10 is string number at left and that's why you can see here we assigned these



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calculations result to this string number at left variable.



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OK.



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Now it says 10 plus because we pressed on the plus operator.



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So now.



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So it is actually a little bit confusing.



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That's OK.



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But if you don't or do not understand it please make sure to watch this part of the video over and over



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again so that it completely makes sense.



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So after all this line of code here I can say 60 results.



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That said text string number at left street number that's left because now this three number at left



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is the result and that's why you can see here the number 10 is going to be district number at left is



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the result here we are going to display this value to the user.



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OK.



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So so now what happens if this if statements that we created here face this if current approach is not



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equal to know what happens if the current operator is not X is actually not ok.



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If the current operator is null then something else should happen.



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This if statement is not going to be executed if the current operator is actually not.



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So in that case you're going to create an if statement here.



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It is really based on your statement you can see that here.



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So when I click on this the curly braces can assure me that viridis anything really bright curly brace



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blanks to.



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So after this ending really brace I'm going to say it's ill's means that if this above part of the quote



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is if this part of the code if counter-protests is actually null then we're going to execute this.



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Else statement we're going to say that three number at liff is actually the current number.



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Semicon So if the user presses on a number the current number is going to be assigned to the string



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number at left valuable.



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OK.



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If the current operator is actually null.



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If there is nothing on the screen let me show you the emulator.



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Let me click on this clear.



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So now the current operator is knol.



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OK.



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And then I press on this number for example number five.



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Number five is the current number the kind of number is now going to be this three but live is going



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to be assigned to this number at left value.



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OK.



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And you're going to say current number assignment operator two code so that it is now completely emptied.



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And then we can actually use it later.



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And here after this statement here we can see that this is the curly brace of our Meffert operator is



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that we're going to say that the current operator is going to be the tapped operator.



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So we call.



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So now at the end of the Meffert you're going to say that the tapped operator is going to be assigned



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to the current operator whether it is if statement here or this statement is executed.



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It doesn't really matter when the function operator is tapped is called The tapped operator is going



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to be the current operator it is going to be assigned to the current operator.



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So for example let me show you the emulator we have number four multiplied by three.



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OK.



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And I'm going to say that plus.



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So now the plus operator is going to be the current operator von multiplied.



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So now we can see that the multiplied multiplication operator is now going to be the current operator.



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So that's why we put this line of code here in order to specify what is going to be the current operator.



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Every time the user presses on the specific operator on our calculator application.



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So now our function our operator is that function is complete.



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Now we need to call this function from somewhere else.



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And you know we want to actually call it we want to call it from that is that these case statements



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and we have some operators here.



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So for example case or ID that BT and plus right we are going to say operator is tapped.



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So what is the top now we need to pass the operator.



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We already know that BT and plus is tapped.



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So if are going to say OPERATOR You're going to refer to our in on call that we created this type darte



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plus Okay.



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And we also have to subtract operator.



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So case our that that BT and said right you're going to say operator is tapped.



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So I think there is a typo in the name of our income.



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So let me scroll to the top.



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You can see that yes there is a typo here.



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Operator So here we need to change the type our instance variable the type of this current operator



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to OPERATOR We need to actually delete this type here and scroll down here.



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We also need to choose the right name for this operator here.



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And for this SBT and subtract we're going to say operator that Cyp tracked this school down here so



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here for this for the name of the parameter of this operator is tap function Vinita right.



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We need to write the right name of right.



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So now the problem is solved with scrotal it up here you can see that for this PTM Plus we called operators



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tappet operator plus and for the speedy and subtract operator that set.



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Right.



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And we also have these PTEN multiply.



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So we're going to see operator is tapped



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operator is tapped.



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And we're going to say operator that Monte play.



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And finally we have this PTEN divide operators tapped



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operator dot divide so that sits.



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So now it's time to run our application.



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Let me show you the emulator.



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So here for example we have number five multiplied by number of free and let me click on this number.



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This plus operator.



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So now you can see the result here number five multiplied by three is 15.



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And we clicked on this A-plus operator plus free minus.



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So 18 15 plus free is 18 and we clicked on this minus operator 1 divided by.



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So here we can see this is number 17 here.



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So it works fine.



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It works perfect.



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So now we're going to do something so that the text we hear at the top is going to show some calculations



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that actually occur here so that we can see what number is multiplied with another number and how the



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calculations worked.



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So we're going to do that in the next story.



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Thank you very much for watching.



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And if you have any questions please sponsor a discussion in of course and I'll do my best to answer



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all of your questions and I'll see you in the next tutorial.