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Control flow is all about deciding where to run code based on if a condition is true or not, or deciding

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if to repeatedly continue running some code while the condition is true.

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This concept is a fundamental building block in programming.

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The most common control flow statements in rust are if statements, and then there are three types of

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loops.

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So let's go ahead and look at what an if statement is.

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So we'll start out by saying Let one equal one, and then we'll we can start an if statement with the

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if keyword.

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So we'll say if one.

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It's greater than zero.

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Print out.

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True.

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So we are checking to see if the condition one greater than zero is true.

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But if it's not, then we want to print out false.

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And that's what the else keyword does.

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Else is going to be our fallback plan.

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If none of these other conditions are true, then this is the block of code that we want to evaluate.

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So we know that one is greater than zero.

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So we got true.

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But if we said is one greater than ten and we ran it, now we fall back to our fallback plan a false.

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That way we have logic for if any of our conditions are not true.

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Another thing that we can do is we can chain in multiple conditions.

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So with the else if keyword.

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So now we can say is one equal to one.

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And if it is, we want to print out equal.

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So now if we run this, we expect equal to print out and that's what we get.

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And you can have as many else if chained together as you want, in order to accommodate for all possible

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conditions that your program might have.

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And that's just the basics to the if statements.

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So now let's go ahead and start looking at some of the loops.

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So we'll comment that out.

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And the first loop that we're going to look at is a while or correction is a loop, the key word being

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loop.

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So to show you what a very simple loop is, we'll say, hey, I just want you to print out loop.

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And this is going to be an infinite loop of.

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The word loop printing out.

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And as you can see, that is what we're getting.

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So we can do control C at the same time.

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And that's going to send an interrupt to our program so that we can exit out of our infinite loop.

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So now let's get a little bit more sophisticated with this loop.

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And what we can do is actually we can give our loop a name.

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So in this case, I'm going to name a loop.

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Called Counter.

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And then inside this loop, I'm going to print out the count

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and I'm going to set it to numb.

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And I need to create the numb variable.

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So we'll say let mutable numb equal to zero.

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And then what we'll do is we'll create another variable.

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On the inside let mutable decrease equal to five.

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And then we're going to create another loop inside of our loop.

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So now we have a nested loop and you can have as many nested loops as you want.

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The more loops you typically have will start affecting your big notation, which is the spatial and

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time complexity that your program may have.

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So inside this loop.

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We are going to print out decreasing.

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And point that to decrease.

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And then we're going to add in some statements.

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So if decrease is equal to four break.

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So this is our first key word inside a loop.

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So what break is going to do is if this condition is true, then we're going to break out of the loop.

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And the loop that this break is referring to is the loop that we're currently running in.

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So the innermost loop.

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But now we're going to create another if statement.

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That says if num is equal to two.

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So our variable up here then we want to break out of counter.

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So this break is actually referring to our outer loop which we.

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Named Counter.

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So what we're going to do now is we're going to decrease by one.

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And what this statement is saying is essentially decrease equals decrease minus one is just shorthand

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for it.

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And then outside of our innermost loop, we want to add one to none.

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And this is the same thing as saying numb equals numb plus one.

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So now if we run this.

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We see that down here.

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We started out with our count at zero.

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That's correct.

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And then we decreased from five.

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Four, which is correct.

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So we enter this loop with our decrease at five.

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Decrease is not equal to four so we don't execute the brake num does not equal to two.

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So we do not execute this brake, but now we decrease by one and we stay inside this loop.

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So now our decrease is four.

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Now we can break out.

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So we break out, we increase our count or numb by one, which is what caused this count to now print

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out one and we repeat the loop again all the way until our count equals to two, and then when our count

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equals to two, we satisfy this condition which lets us break out of our outermost loop, which we named

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counter.

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So again, you can have as many loops as you want inside one another.

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And then based on your logic, you can stay in a loop as long as you want, and then you can set up

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logic on the inside to be able to break out of loops when conditions are met.

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So another type of loop that we're going to look at is called a while loop and a while loop will run

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while a condition is true.

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So to very simply show this one, we're going to say while well, first off, let's create a mutable

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num equal to zero again, and then we'll say while num is less than five.

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Print out.

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Num.

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I want the value.

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We'll reference our number and then we will add one.

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So now we'll run it out.

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And you can see that we printed out and got zero, one, two, three and four and.

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Once we hit five with numb, our condition was no longer satisfied because five is not less than five.

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So we broke out of the loop.

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But now if we said less than or equal to five and then ran it, now we also included five.

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And that's how a while loop works.

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So now let's look at a for loop.

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In a for loop.

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It's a great way to loop over elements of a collection.

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So think of a vector.

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So let's do vec vec of i eight equals to 0 to 10 and then we want to collect those values and put them

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in there.

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So then four element.

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So to start a for loop we use the four key word element is going to be our variable for accessing all

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the values inside.

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So for element aka all the values inside our vector in and then what's our actual vectors name that

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we want to reference.

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Well it's vec.

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So for all the values and vec.

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Let's print them out.

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Print one.

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And then we want to print out what the element is.

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And as you can see, we printed out 0 to 9, which is what we expected.

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So now a fun, little cool one that I can show you.

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Is we can create a four number in 1 to 4 and then.

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Reverse it.

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Current line.

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And then we want number.

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And then afterwards, when our countdown is done, we have liftoff.

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Clear.

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Run it.

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Three, two, one.

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Lift off.

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So we created one, two, four.

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Not including for reverse it, print it out and then exit the loop and provide or print out, lift off.

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And that's all it is to loops.

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So loops are very powerful.

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You're going to use them all the time throughout your code.

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But now we have successfully gone over all the basics of programming.