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Hello and welcome back.

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In today's lesson we are going to look at subroutines which are also known as functions.

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So go ahead and download the file 0 6 subroutines functions it and put it in your fascinating project

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folder and then zip it

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and it is easy for now you have a new folder 0 6 subroutines functions so many and you receive the four

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of us here.

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One is the add two names are some file and another file had two nuns three functions.

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That means this file is run he's written not using any functions but this code.

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This program is written refactoring.

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So let's take a look at the first one first.

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So this program prompts I use it to enter two numbers and then then prints the result.

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So let's run it click on run compile

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and let's go through this coded after compiling it has this file.

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Yes he has

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time out at least the directory and you should have this far.

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So let's run it now

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a promise.

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Enter first number.

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So we enter three presenter.

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You can enter any number.

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Then it prompts you to enter the second number.

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Let's enter five.

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Again you can enter any number you like PRESENTER Any prints result eight.

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So it took the number three he took the string three and convert it into number.

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And then a two then the the string five and converted it into a number and added it to number to produce

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eight.

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So let's see how it works.

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So we have a few strings here.

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The first two string into num one is two probably four the the first number.

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The second string enter number two is a promise to enter the second number and the third string message

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is to output a result and some is in teacher 0 number.

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It is used to store the result of adding the two numbers together.

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And it is initially set to zero so here you have one two three four five.

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We have five numbers.

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Didi missing data double giving this data bytes so to go with here are numbers.

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So you're declaring five numbers.

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So the first two number is for storing the input handle used by the API function and vice red is to

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keep track of how many invites have been read by the Windows API can refile.

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And then number one is the star the number that has been converted from the string so when it enters

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a string he will be converted to number and start here.

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Same thing with the two input string is the string that is being read for example three he'd be starting

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his input string first before it is converted to a number and start in number 1

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and in also our starts the second number as a string before it is converted into a number and start

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in number two.

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You program starts you ask.

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Easy to enter a number by printing that from and then on one.

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So here in the number of print Enter first number

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then over here you've written a number issues enters.

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So these are type 3 which is a string and the string is three start in this terrible input string thereafter

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you use a string to all you have a function to convert the string into a number.

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And this 10 and a B starting he has to register in order here we shift and he s really set value in

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a variable call them or.

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So number one we store the number three then it is a user would then be prompted and enter a number

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so these types five finally this tiny string.

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And again he would be converted into a number.

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So file become with a number and start in E X NBER this number into another variable call.

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And the two.

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So number two in our stores.

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Five.

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And number one stars.

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Three how we are going to add two numbers.

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B 0.

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He asks because we are going to use the s to sum up the numbers and we had number one two idiots and

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stark idiots.

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So he number one starts the very tree and he s is zero initially so triple zero is tree and trees there

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is a tree start in he s so it s not becomes tree then we take the number two is contains no Fi and added

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2 Three he reaches edicts so 5 plus three is it and the result it is starting back into ADX then we

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soon copy some idea into another will cause some so it is an dies and it is not being saved into a sum

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so somehow becomes 8 and now finally we print the result how by putting some in to the stack and push

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up a message and then copying it.

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So these two are the two parameters to print f.

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So our whole message contains this string and a format specify.

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So percentage these is used to print out numbers and he will be replaced with some.

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So we get the results result hit.

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So as you can see this program is quite quite long because we are repeating a few things over and over.

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For example here we repeat repeating this here read the number converting to string.

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So it has a better way to do this.

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We don't want to keep repeating things over and over.

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So what we can do is we can take this and convert it into a function subroutine and improved version

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is over here.

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So in this second equation how police on the left hand is in the right.

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We have taken we have taken this out and put it into a function.

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So this is a

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if motion is from here the function get num starts here and function going on here and we give it a

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label.

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So it is the name of the function or the subroutine and you can see now this part here may be read from

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the console is found over here and this by here we convert string to number is fun.

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Or here and then we have something new here called written.

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So the function runs from here and then you finishes executing a return you return to the caller now

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Cody shorter instead of writing this.

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Now we just have a call the new function here.

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So one line here replaces all these lines here.

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So we call get num he would jump to their function executed and then when he hits the written instruction

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he would go back to the next instruction after the call which is move.

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So this function when he finishes a restored the result.

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In each case that means he has to contain the number the last functioning the insight needs and get

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numb is to convert the string into a number and that number is tiny.

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So many returned from this file Hinkle we will now start that he checks into the variable number one

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just like what we do in our weekend program.

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After that you probably use a two in there a second number and then you will call again.

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Canon once the function returns he will start the value in a second variable.

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Number two.

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Now notice that once you finish with the second call to the function and is starting the result of the

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second number in number two you are now ready to go to the next part of the instruction which you know

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in Django where all this function.

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So we do that by using a gem in jump up with Riza who jumped all the way past this function.

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Come down here and over here you add the two numbers together so you will first initialize the X to

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0 and then you add the number one mediates at number two tedious and then move the S into the variable

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sum and finally print the result.

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So now code is shorter.

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We don't have to call these few lines twice so our code each other as you'd see in the original code

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you find these two lines here.

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These two functions here and using being repeated again down here but oh here we replace those with

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one com and here is another call.

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So these two costs make it short.

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So another code is neater a shorter OK.

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This is not a new thing here.

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Notice.

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Instead of fashion I added these two lines.

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EVP and movie here speed EVP and here I also added this one I probably maybe now when you're writing

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your own functions you should always do this.

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This is called The Function Prolog and this is called The Function epilogue.

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The reason why we do this is because we want to preserve the register EVP why do we need to preserve

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EBV because GBP is used as a pointer to the stack frame.

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What is a stack frame as time frame is uh part of a stack.

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We started the main program and any of the CHA programs we are Cha functions which are running twice

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under when you first start this program.

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This whole program start from the start entry point so the entry point you will be pushed to the stack

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by the operating system and the entry point will have its own base address which you start in EVP.

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So when the main program calls in and a function you will then move to execute the function.

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But when you go to execute in the subroutine or function the central theme function might call up EVP

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but maybe using it inside is.

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So to maintain the original values in EVP the CHA function will always push the original EVP value to

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the stack to preserve its original value and then we'll pop it back to restore the order value when

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it finishes.

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So that is why we need to do this.

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And what is the reason for this line.

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So this line is optional.

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Now why we use this is because we want to use ESB in site here so ESB can be used in say a child function

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or subroutine when you want to create local variables.

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But in this case here you are not creating any local variables.

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So for now you can use a notice since you are not creating any local variables but it is good practice

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to have a habit of writing this as well.

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So whenever you write your own user defined function they should add these two lines plus just.

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Now if you recall in the early lessons on unpacking we also saw that we need to keep a lookout for EVP

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push EVP and probably be.

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So now you understand why we need to write this when we are creating our own user defined function.

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So if you forgot about the unpacking go and revise the attacking chapter since they we discuss why we

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need to keep track of pushing VPN properly so that's it for this program let's take a look at the second

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program.

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The second program is a new program which we studied before.

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Compiling and now we have a look see.

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So let's run it.

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Let me clear the screen first and then run the loop and then no.

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And then as we enter 5 he prints one up to the number that we enter.

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So we did this before in the previous lesson.

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So I'm not going to go through it again.

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So remember this look.

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Now this look is quite long because the implement the print f inside here

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so this makes it longer to make the court more neater and more efficient.

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We can factor this up and put it in a separate function.

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So let's take a look at the function version of this program looks a function.

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Here you see

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now we have uh call call call to print Current um print Konami search function we should be fine here.

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So notice now he said of these uh four lines.

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He replaces the one single line one single line and the effect out and this into a separate function.

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And notice here again we have this function Prolog and the function epilogue and the return keyword.

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So whenever these look runs when he comes to call he will call this function will and print a number

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and then you return.

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And if he shows so when he returns he always returns to the line after the call.

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So this is how the written was right let's run this nice comparison runs to make sure it works.

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So now let's try the version where it functions and the number is a 6.

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And it works.

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So okay so now you know how to create your own functions and subroutines to try to convert any program

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to one issue land before in to another version using functions.

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So that's all for this lesson.

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Thank you very much.

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House here the next one.