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In this video we'll be looking at repetition statements in C sharp.

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I have already created the project and this time the project's name is repetition statements and I have

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already set up the comments to guide what we will be looking at.

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You may pause a video here and go ahead and create the project and set up your code file to look at

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mine.

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Now we've already reviewed two cons control structures.

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We looked at sequence where that is the order in which the code will execute.

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So from top to bottom the way you write it the way it will be executed.

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Then we looked at selection where we get to a situation where we need to compare two values and then

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take an action based on the outcome of that comparison.

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And that selection more making a decision.

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So no we're going to look at how we repeat an action without having to type the line more than once.

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So in our previous example where we were looking at selection and I'm just going to go over to my condition

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statements project and click on that program not see us.

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We printed the same line four times.

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We were literally wrote this line four times.

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Now there is a way that I can repeat this action without needing to repeat the line because no if I

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wanted to change the sentence then I have to manually go in and change it for different times whereas

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if I could repeat printing this sentence four times without changing the sentence or rather repeated

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four times.

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But then I need to change a sentence then I would only need to change a sentence once but it would still

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go four times.

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So that's the advantage that loops bring to us the ability to repeat an action.

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So you see that I have outlined three types of rules that we'll be looking at today.

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There there is a fourth and I think there is also a fifth but then for no I'm just looking at these

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three because these three are mainstays and they're in every single language that you'll ever do.

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And the other one kind of has special applications which we'll be looking at later on.

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So the for loop is what we call a counter control loop.

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So counter controlled meaning I am setting the number of times that I want this repetition for.

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So if I wanted something to happen four or five times then I can specify that I want to type in five

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times no fewer and no more.

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So let us look at the syntax for a for loop.

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So it starts off with the keyword for and then we open parentheses and then inside of the parentheses

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we have a few things that we need to do one we need to define what we call the counter so a counter

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is going to keep track of the number of times it is being executed.

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So we need to me at the column to have a base value.

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And I'm just going to say I I short for iteration does that really matter.

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You're going to variable can have any name you would call it count.

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But just make sure you have a variable there.

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So I'm calling it I so into I is equal to zero.

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So I'm initializing my counter to something that is very basic very low in value and I'm starting at

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zero.

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Then I have a semicolon then I see I less then and then I'm going to give it the value that it should

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always run to be less done.

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So here's where it can get tricky and I just I'm going to try my best to explain it so that you understand

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why it's going to be written this way.

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So I would just say I.

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Which is going to have an initial value of zero less than five and then semicolon again and then I close

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plus.

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Now let me explain what's happening here.

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So I have a call center and I'm initializing it to zero.

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Then I have a condition where I'm seeing repeat as long as this condition is what as long as it's met

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then continue to repeat yourself.

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And then I have this section which is the incrementing seeing that the counter variable is counting

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how many times it runs.

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So I wanted to run five times on the first thrown it will have a value 0 0 then it will do the comparisons

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is 0 is less than 5.

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Okay then it runs and then it's increments.

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So no I is 1 then it compares is 1 less than 5.

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It is then it runs again and then it will do that and do that until we get to I being equal to five

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and then it will take a five is less than five which we all know is not true.

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Five is not less than five five is equal to five.

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So then it will exit the loop.

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Now you're probably wondering okay.

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So why the zero and why compared to let's say less than five.

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Well if you put your hand all right.

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No and do the math and you count zero.

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That's one finger.

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One two three four.

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Then you would have counted all five fingers on your hand.

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So it's typical practice to actually start off your column to zero and then just let it that the com

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pirates are on it until it is less than the number that you wish to stop at.

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Right.

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The alternative would be if I started this at one then I would have to change my condition to see that

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I should be less than or equal to 5.

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So we would have looked at the less than or equal.

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Very very briefly in the selection section.

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But what I'm trying to point out is that typically if you look at any other example if you pause this

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video and go and google a for loop example you're going to see more often than not that the initialize

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the contour to zero and then they made the condition run until it is less than the intended number of

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executions.

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So it is zero then turns to one that it turns into it and it turns to three then it turns the four at

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the point it turns the four the loop would have executed five times.

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So when it becomes five it does this comparison I realize that this is not violated.

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And then it will exit the loop.

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So that just part one off writing are for loop.

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So then after we do that then we need our braces so you notice that curly braces are like a mean state.

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Functions need them if statements need them.

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I know we see that loops need them.

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Right.

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So whatever we write inside of the curly braces would constitute the action that is being done each

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time.

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So let's just say I want it to print I am a winner five times so I want to say console Dot.

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Right.

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Line right line and then that takes them writing to the screen is I.

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Winner with an exclamation sign in case the all caps wasn't clear enough.

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All right so I am a winner and I want that printed five times to the screen so remember that when in

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the early example I did it manually by writing the line multiple times.

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This time I'm writing it once but I wanted to print out five times so I'm going to just switch my starter

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project quickly to repetition statements and then we're going to look at this and see if how many times

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is going to print.

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All right so then we see I am a winner being printed five times so this was the time he got printed

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while I was 0 and then it went around.

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So did the action then it hit the current to brace.

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Then he came back to 1 increments.

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So he did and I plus plus it incremented from zero to one and then he did the comparison to see is I

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still less than five.

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It was so rare and again and then it did the same thing came back incremented.

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So no I was too.

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And then that comparison happened.

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I realize it was less than five and then he came back and then it went to three and then it went to

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four.

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And then when it hit the four and then it incremented and no I had a value of five.

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It did the comparison and five is not less than five.

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So this this condition was not violated.

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So it came back to the curly brace and then exited.

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So whatever else would've been on the here and let's just say I said to console that right line.

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And then this is a nice cool way to get like some space.

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So if you want like a blank space between two lines you know a console.

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Right.

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Line I wanted empty space again just a console.

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Right.

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Line and it gives you a blank space right.

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And I just duplicated by pressing control D so just by being on the line control D and I will duplicate

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the line and that I'm going to see for loop finished.

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All right so let's try that again somewhere to execute this one more time and then here we see that

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it executed everything and then when it exited it continued to execute the rest of the court.

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So that's once again sequence.

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So it won't move on until all of what it needed to do inside the loop was done which was to print this

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five times to run five times and do whatever I told it to do four or five times.

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And then once it finished it went on to print the blank space.

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That's a empty console the right line and then print for loop finished.

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Now I'm going to do a little modification to what those inside a for loop I'm went to print another

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line so remember that as many commands as you want to repeat we can put as long as they're inside the

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tool brace someone to console that right line.

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And this time I want to print the value off the the incrementing variable or the column to write.

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So this time I'm going to see a counter and I'm just going to put a call on and then I'm going to use

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my interpolation and then plug in that value.

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So I'm just going to see I.

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All right.

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So each time that the loop runs whatever value I has I am going to be printing it to the screen just

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so you can see that it starts off with zero and goes up to four.

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But it would ever run five times.

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All right.

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So let me try that again.

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All right.

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So now we see I am a winner and a calendar value is zero then I am a winner again.

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Clinton value goes to 1 then to two then to three then to four.

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So zero one two three four equals five executions.

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All right.

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So it's good practice to understand why we start to zero because when we get to arrays and collections

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then you're going to understand that the computer actually starts counting from zero in as human beings

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we tend to ignore zero and we start counting out one sure but the computer starts counting at zero.

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So it's good to appreciate why we would start counting from zero.

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That being said I didn't necessarily have to start from zero.

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I could have started from 50 encode to 55.

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And so I could have said the Coalition should start off as fifty five.

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And it should execute until it hits 80.

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All right.

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So whatever number of times it's going to go between 55 and 80 or if you do the math and say 80 minus

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fifty five whatever number you get that's the number of times it's going to execute.

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All right.

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So if I just do that quickly the end result of that is this line I am a winner and the columns are being

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printed from fifty five which is a valued started with up on to seven to nine which means that when

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it hit 80 it violated this condition and jumped out and that's pretty much it for for loop.

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So this is a very simple example but I hope that you appreciate it.

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So I'm just going to reset this code so that when you look at the example you see it and I'm just going

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to add sample printing five times all right.

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So now we have some comments to guide what this is doing.

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All right.

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So let's move on to the wild.

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So the while loop is what we call a condition control loop and then I appended that with the expression

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free chick.

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So when we do the do while then you'll see what the pre vs. the post really mean.

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But right now I'm just going to focus on the condition control so the condition control portion of it

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means that it is going to continue executing until a condition is violated or it will continue to execute

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while a condition holds true.

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So with our for loop it was called into our control which means that we're just executing for a finite

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number of times because we know we wanted to do five times so we specify or we rotate in a way to make

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sure that it doesn't exceed five times.

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However if we want something to go on and on and on and on until a particular condition is met or are

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violated then we would use something like a while loop.

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So the thing is know that with a while loop you can run into what we call an in finite loop where if

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you write the code for the while loop and condition never gets violated it will never exit that loop.

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And so it will run on and on and on.

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Right.

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As long as a computer is on and whatever conditions are required for it to be running out there it will

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just continue to execute.

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So I would just start off by showing you an example of an in finite loop with the while loop Fred.

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So I want to declare a simple variable and call it and I give it to value 0 0 that I would to say a

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while n is equivalent to 0 and I noticed the syntax we have the keyword while we open the parentheses.

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And then we put in our condition just like we would have done with the if statement.

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Right.

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So the only difference between it and the statement is that instead of saying if we see a while.

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All right.

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So we see a while open bar indices put in the condition and then open curly braces with our actions

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right.

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So the way I've written this and is not going to change from zero.

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So this is going to say a while and has the value or is equivalent to the value zero.

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I want to do this.

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Someone to write two lines and just copy existing lines.

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Someone to print a blank line and then I'm going to see in while loop.

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All right.

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So while the loop is running it's going to print I would say in a while loop and then the blank line.

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So it's going to see in side to say inside while loop and we're printing a blank line after that.

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No I'm just going to comment this out quickly so that it doesn't get executed while we run this program

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because no I want to focus on the while loop and you're going to notice that it's just going to continuously

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print and never stop.

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So let me execute initially.

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And that's what it looks like.

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So yes he's just printing printing printing printing printing and seeing inside while loop and you can

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see that it can as a blank space you look at a scroll bar I see that it's just going on and on and on

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and on and on it's never stopping.

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And that's what do we call an infinite loop these infinite loops are known to break computers.

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So if your computer crashes who and you do this I'm sorry.

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But I have a slightly powerful machine so at least I know that this won't break my machine.

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But the fact is if you're right poor code in big applications and you get this or end up with this situation

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these situations are in finite loops can bring down systems.

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All right.

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So you want to make sure that you understand whole while loops work so that you don't make this mistake

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at any point.

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All right.

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So let's exit that and look at how we should write while loops to make the most of it or to take advantage

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of the condition why not leading to an infinite loop.

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No.

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Our condition is based on the fact that n is equivalent to zero.

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So it's going to run away.

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And sorry is equivalent to zero.

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So what if I change this and I said something like While n is less than five.

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All right.

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So while the value of end is less than five I wanted to do this.

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No based on the way it's written this will still be an infinite loop because any 0 0 is less than 5.

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And I'm not doing anything to change the value of n.

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And so it's going to always be less than five until the continent executes.

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So that means the one thing I can do to make sure that this gets violated eventually is to make sure

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that I am changing the value or putting something in place that the value changes at some point.

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And this comparison will get broken or this condition will be met or violated or other at some point.

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That is convenient to how we want our program to work.

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So I want this to print five times.

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Yes we accomplished something that that with a for loop but I'm just showing you that I can accomplish

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something that that with the while loop but the the path to doing so is going to be very different.

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So I need to know make sure that I am changing the value of an to be something that eventually will

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exceed a value that makes this condition true.

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So I'm just going to add a third line to inside my while loop and then I'm going to see an is equal

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to N close 5 or sorry n is equal to any plus 1.

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So when I say n is equal to N plus 1 remember we discussed that this could be shortened into just seeing

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n flows equal one.

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So no it's going to be adding 1 to itself each time.

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Right.

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So it's going not by a one until eventually it will execute and n is going to have a value that is not

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one to make.

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That's not one to be less than five.

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So our while loop will exit.

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So let's this.

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That's 0.

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So I mean execute.

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And here we see that's literally printed the right number of times.

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00:17:51,220 --> 00:17:56,610
So just like with the for loop where we started off a zero and went to it was less than five.

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We started off with n being zero and then we're just checking on the condition that n is less than five.

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But there is nothing in the loop or in the structure of the loop that at least not naturally that will

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help us to change the value of.

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And so we had to do that manually by putting an accumulation so we'll call this an accumulator.

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When you make a variable increment by itself plus another value.

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Right.

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So when I said n equals N plus 1 that's making it an accumulator are plus equal.

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So now I'm accumulating value each time it runs and then eventually we'll be will meet this condition.

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Now this is a very simple and not very practical example I mean there are situations you may use this

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but a more useful way for using the while loop is to see compare user input and let that user input

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violate the condition and continue to do this until the user violates the condition and the loop will

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exit.

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All right.

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So so let's take your experience with an ABM for example on ABM will probably always ask you do you

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want to continue if you say yes it continues if it says no.

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And then it repeats the same steps on as long as you keep on seeing yes.

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All right.

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So literally all they have is really a while loop that is allowing you to do carry out operations and

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then you can indicate when you want it to stop.

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And then when you give it the condition that C is stopped then you will say OK that condition has been

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violated.

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Let me move on.

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So I'm going to modify this and I'm going to see console the right line and I want to tell the user

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input no all right.

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And I'm going to say zero to four.

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So I'm telling the user to input some number between 0 to 4 and then I'm going to do I read line where

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I'm going to see and is equal to convert to sorry spell converts wrong convert to in thirty two and

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then I'm going to say a console dot read line so I'm accepting user input and I'm not going to increment

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because I have the user determining the value of and each time right and I'm going to take oh this console

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00:20:28,680 --> 00:20:37,050
that right line Well let me put it back and then I'm going to print the screen you entered and I want

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to see you enter that number.

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All right.

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So let me just put on my dollar sign interpolation.

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So what this loop is expected to do is that or it's going to from the user to enter a number if I enter

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0 then if I enter 0 then it will print to you entered 0 and then it's going to come back and it's going

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to check the condition is 0 less than 5.

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00:21:00,810 --> 00:21:06,030
No it's not so it's going to see in turn number again and then it's going to continue doing that until

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I put in a number that clearly is not less than five or will clearly violate this condition.

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So let's try that so input a number and I put in three press Enter you In you entered three and then

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it's prompting me again.

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So I entered three.

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It printed that I entered three and then it came.

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Did the comparison realize that this condition is still true because three is less than five.

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00:21:34,090 --> 00:21:36,610
So it went ahead and asked me for another number.

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00:21:36,610 --> 00:21:38,770
If I put you in for it we'll do it again.

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00:21:38,770 --> 00:21:46,600
If I put two in one if I put you negative five as long as a number is not let alone as the number is

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less than five then it will continue to do this operation.

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If I put in ten it will exit.

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00:21:54,130 --> 00:21:57,880
All right so let me put in a proper statement to say it has exited.

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00:21:57,970 --> 00:22:04,960
So I'm just taking this previously written one on commenting it I see keyboard chakras just make it

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00:22:04,990 --> 00:22:06,130
easy to maneuver right.

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00:22:06,160 --> 00:22:10,860
So while loop finished all right.

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00:22:10,870 --> 00:22:12,210
So let's try that again.

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So we have zero to four output zero.

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I put five and then oil.

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OK.

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00:22:18,220 --> 00:22:19,340
So I entered five.

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I did that prematurely but that's fine.

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So I entered zero and it just said OK zero is this and five from Tim again.

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Then I entered five.

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00:22:26,950 --> 00:22:29,840
It came to the comparison five is not less than five.

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And so it just went down to the square to brace and then continued with the execution where it just

321
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said while loop finished.

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All right.

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00:22:37,960 --> 00:22:44,260
So that's basically how we can use while lose because once again it's going to run against a condition

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and we want to make sure that this condition can get violated and legitimately so because if we don't

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do that then all the operations that the while loop is repeating will be repeated until that computer

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shuts off.

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00:22:58,630 --> 00:23:04,240
And that can lead to lead to some buffer or a memory overload and all sorts of things that we don't

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00:23:04,270 --> 00:23:04,690
want.

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00:23:04,720 --> 00:23:12,460
So when the writing condition controls loops make sure that the condition can be violated at some point

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and legitimately so.

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Now we move on to our do while and I did say that I would mention the pre vs. post.

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00:23:20,350 --> 00:23:25,480
So the reason we call The while loop the pre check is that is going to check this condition before it

333
00:23:25,540 --> 00:23:26,700
executes.

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00:23:26,710 --> 00:23:34,840
So if I initialized n to have a value of five or let's say 10 then the first thing is going to do is

335
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check is this condition true.

336
00:23:36,910 --> 00:23:43,480
That's the pre check is the condition true is if any 10 and 10 is not less than 5 then nothing here

337
00:23:43,480 --> 00:23:46,850
will get done it will just move on to C while loop finished.

338
00:23:46,870 --> 00:23:51,560
So that's a pre check the post check will do it before.

339
00:23:51,580 --> 00:23:55,120
So it will do the action and then check the condition.

340
00:23:55,120 --> 00:23:55,730
Right.

341
00:23:55,750 --> 00:24:02,230
So let me just write the do while and I'm going to do the same operation inside to do.

342
00:24:02,590 --> 00:24:06,850
But then we'll see the difference in the execution.

343
00:24:06,850 --> 00:24:15,280
So the syntax for our do is the word do the or we open and close the curly braces and then on the close

344
00:24:15,280 --> 00:24:20,430
currently brace you have to see while and then you put in your condition check.

345
00:24:20,440 --> 00:24:22,870
So the wild part looks just like the regular while.

346
00:24:22,870 --> 00:24:26,570
So I'm just going to copy this and pasted down here it looks the same way right.

347
00:24:26,590 --> 00:24:32,110
So the only difference is that we see a while and then opened the curly brace the do while we say do

348
00:24:32,140 --> 00:24:38,230
this action do whatever is inside the curly braces and then check the condition afterwards.

349
00:24:38,230 --> 00:24:41,560
And then this one requires a semicolon at the end of it.

350
00:24:41,560 --> 00:24:46,690
So that's where it can get and can get kind of tricky because then you see that oh no semicolon and

351
00:24:46,700 --> 00:24:49,140
semicolon for this one on there and there.

352
00:24:49,150 --> 00:24:53,930
So reinvention is just practice that will make you get used to where to put the semicolons and where

353
00:24:54,040 --> 00:24:59,860
we're not to write and visual studio is always ready to give you that encouraging red line to remind

354
00:24:59,860 --> 00:25:02,240
you that hey there's something missing here.

355
00:25:02,260 --> 00:25:08,530
So then it's telling you semicolon is expected you put it there and all is well in the universe after

356
00:25:08,530 --> 00:25:09,060
that.

357
00:25:09,100 --> 00:25:15,670
So I'm just going to copy these actions quickly put inside the do and put that into space so we can

358
00:25:15,670 --> 00:25:24,500
see exactly what's happening and then output the statement that tells us when the do while loop is finished.

359
00:25:24,890 --> 00:25:28,210
So I'm not actually not want to come in this autumn winter to run it.

360
00:25:28,220 --> 00:25:31,200
So the value of n is 10.

361
00:25:31,400 --> 00:25:37,640
Remember that the pre check is going to check the condition if the condition is true then it will do

362
00:25:37,640 --> 00:25:45,050
what it's what what we told it to do and then it will come back and check the condition again if the

363
00:25:45,050 --> 00:25:48,860
condition is not true then it will not do anything.

364
00:25:48,890 --> 00:25:49,420
All right.

365
00:25:49,850 --> 00:25:55,220
Whereas with the door while it will do something and then check.

366
00:25:55,220 --> 00:26:02,750
So that means I have the opportunity in this one to change the value of n from 10 and then it can change

367
00:26:02,750 --> 00:26:09,410
whether you can violate that or it can make it true so it will just say oh this condition is true let's

368
00:26:09,410 --> 00:26:10,100
do it again.

369
00:26:10,130 --> 00:26:12,530
So we'll do it at least once.

370
00:26:12,530 --> 00:26:13,300
So let's try that.

371
00:26:13,310 --> 00:26:19,580
So I click Start I notice the first thing that's printed the screen is something to tell us to do the

372
00:26:19,580 --> 00:26:20,630
while loop is finished.

373
00:26:20,630 --> 00:26:26,210
So you know it just skipped the doorway as I said it just check the condition 10 less than five.

374
00:26:26,210 --> 00:26:26,940
That's false.

375
00:26:26,940 --> 00:26:27,250
Ah.

376
00:26:27,280 --> 00:26:28,580
Don't bother with that.

377
00:26:28,640 --> 00:26:32,810
Print the blank line and then give me the while loop finished.

378
00:26:32,900 --> 00:26:40,010
But then the door while is asking me for the number so it's doing the action and then it's giving me

379
00:26:40,010 --> 00:26:43,790
the opportunity to put in the number and then it will check the condition.

380
00:26:43,790 --> 00:26:44,340
All right.

381
00:26:44,390 --> 00:26:49,270
So if we want to do something at least once it's a repeatable thing well you want to make sure that

382
00:26:49,270 --> 00:26:51,760
it happens at least once.

383
00:26:51,860 --> 00:26:53,790
Then you want to use a do while.

384
00:26:53,840 --> 00:26:54,170
All right.

385
00:26:54,500 --> 00:27:00,980
So then I want to input a number and let's say I input three it will repeat.

386
00:27:01,010 --> 00:27:01,370
All right.

387
00:27:01,370 --> 00:27:06,590
So when I entered three on prompt then it hit the condition and three is less than five.

388
00:27:06,590 --> 00:27:11,860
So it said we'll do it again and then this on with to enter five or what I've said fifty six.

389
00:27:11,870 --> 00:27:12,740
That's fine.

390
00:27:12,740 --> 00:27:16,100
And then entered 56 which is clearly not less than five.

391
00:27:16,160 --> 00:27:21,180
And so it just went on to say while loop do while loop is finished.

392
00:27:21,200 --> 00:27:27,110
So that's the only difference between the while and the do while the do does it at least once and takes

393
00:27:27,110 --> 00:27:31,980
after whereas a while loop will do it will check before it does.

394
00:27:32,240 --> 00:27:37,370
And then we remember that our for loop and others on Comment is before we wrap this up.

395
00:27:37,670 --> 00:27:44,300
The for loop is set to run for how many times we want it to run.

396
00:27:44,360 --> 00:27:47,740
That's it for petition statements in C sharp.

397
00:27:47,940 --> 00:27:51,820
Remember to practice and think of scenarios where you may need them.

398
00:27:51,860 --> 00:27:54,500
We're going to be using them more in our project.

399
00:27:54,500 --> 00:27:57,110
But for know this is an introduction.