So, how long should I expect to wait if I'm setting a timer for 10 minutes? Probably 10 minutes. Pretty much know what that is. How would you compare that to the following situation? How long is it going to be when I'm done playing this game, old-school PacMan until I run out of lives? Those are different right? 10 minutes, I know when that timer is going to go off, and as any parent who's dealt with children who wanted to play their games longer, how long do you let them play the game? Is it a fixed number of minutes until they run out of lives? Challenging decisions. What about this situation? Well, if on the left, I'm at home and we have cleared all of the dishes from dinner off of the table to sit to the left of the sink. How many dishes am I going to do before I'm done? Well, there's a pile of them, I can count them all, I know exactly how many I'm going to have to do. Compare that to the situation above, where let's say, I'm a professional dishwasher in a restaurant. How many dishes am I going to have to do during my shift working at the dishwasher? I don't know. How many people are coming in that day? How long is my shift? What kind of dishes are being made so that I know how many dishes that need to be washed? So, this brings up a key thing about repetition that exists not only in the real world, but also for computers. That is, is the number of times that I want to repeat something in the real life say, is it a fixed number of things? Is it 10 minutes, is it 40 dishes, or is it conditional? Is it depend on something else? Is it depend on how good I am at playing PacMan, does it depend on how many people are coming into the restaurant? So, this is a core difference that we're going to explore. We've looked at fixed before, now we're going to look at conditional. Let's explore a bit more together. Here's fixed, X number of dishes, here's conditional, how many people come in. Here's fixed, 10 minutes, here's conditional, how many lives they have left? Fixed, a particular number of times, a number, an integer, a whole number, in this case of how many times I'm going to repeat something conditional, what else? Alright, so you try. Is this fixed or conditional? Suppose, I'm this person at the checkout aisle on line one, how many people am I going to check out in my shift, or even in the next hour? Yeah, I'll call that conditional. It's really going to depend, how many people come into our store? Are we having a closing sale and like everybody is there to try to clear everything out? Is my shift in the middle of the night, and there's not that many people? You just don't know how many people you're going to be checking out in the next x minutes. We can't put a given number on it, there are other things that could depend on. How many items each person has, so how long does it take me to serve each person? Etc. So, there's a lot of conditions that might impact how many people I'm going to have to check out in the next period of time. Here's another one, you try it. Is the number of times that I'm going to spin this dial to open a traditional combination lock fixed or conditional? Well, you may or may not have experienced with the combination lock and it might have been a long time since you have, but it turns out it's fixed, that you can go and read the Wikipedia article online, you need to turn the knob right three times, left two times, and then right one time. What else in the world is repeated a fixed number of time, or conditional a number of times? Let's have you think about it, and let's have you think what students in K-12 might think about this.