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Hello, dear friends.



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In this lesson, we're going to try to understand conditional statements in Python.



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We're going to do it.



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Come on.



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So let's start.



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So first we're going to talk about control statements.



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But before that, we need to know about decision making and why we need it.



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So decision making is anticipation of conditions occurring while executing the program and specifying



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actions taken according to those conditions.



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Decision structures evaluate multiple expressions which produce true or false as their outcomes.



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So we need to determine which action to take in which statements to execute if the outcome is true or



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false otherwise.



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So the following is the general form of a typical decision making structure found in most of the programming



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languages.



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These conditions can be used in several ways, most commonly in if statements and loops.



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The Python programming language assumes any non-zero and nominal values to be true, and if it is either



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zero or no, then it's assumed to be a false value.



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Great.



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So now we're ready to learn control statement.



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So our first control statement is the if clause.



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All right, so what is the statement?



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So the if statement contains a logical expression using data to be compared, and then a decision is



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made based on the result of the comparison.



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But how does that work?



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Well, if the Boolean expression evaluates true, then the block of statement or statements inside the



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if statement is executed.



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And if a boolean expression evaluates to be false, then the first set of code after the end of the



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if statement or statements is executed.



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I'll tell you what.



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Let me show you some examples, and we can both understand it a little bit better.



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So create a variable named age and ask for the value to be entered by the user.



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So if the age is less than 21.



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Prend.



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You can't enter this place.



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Now, if the user entered value as lesson 21, the program will return us so you can enter this place,



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but the user entered value is equal to or greater than 21.



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Then the program will return us.



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Nothing.



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Right, because we didn't mention him.



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So let's create another variable named number and we'll ask again for the value to be entered by the



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user.



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If the number is less than zero.



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Print negative.



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So now if the user entered values less than zero, that program returns us negative as a result, but.



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The user entered value is equal to or greater than zero.



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The program will return as nothing.



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Yes, because we didn't mention it.



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Right.



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That's as it should be.



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As you can see, we can we well, we're going to just need more information to make the program functional.



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That's why we need to know the else statement.



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All right.



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So what is the P&L statement?



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And our statement can be combined with an if statement and statement contains the block of code that



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execute if the conditional expression in the if statement resolves to zero or a false value.



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But how does our.



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Wow.



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Let's see some examples.



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So first, let's use our examples again and and the else block to the end of it.



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If age lesson 21 prent you can't enter this place else print.



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Welcome.



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Now, if the user entered values lesson 21, the program returns us.



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You can enter this place, but if the user entered value is equal to or greater than 21.



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The program returns as welcome.



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And as you can see, our code is becoming more functional.



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Right.



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So let's do it to the other example.



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If the numbers of us and zero print negative Nel's print positive.



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So now if the user enters a value that's less than zero, the program will return as a negative value.



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But if the user enters a value that's equal to or greater than zero, then the program returns us a



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positive result.



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So what if we want to create an el statement without using if.



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Ha.



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All right, let's try it.



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Else print hello.



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OK, so as you see, Python returns an error because an else statement is an optional statement, and



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there can only be at most only one L statement following if you follow.



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So now we can talk about our last conditional statement, the Ayliffe statement, the L.F. statement



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allows us to check multiple expressions for true and then execute a block of code as soon as one of



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the conditions evaluates to be true.



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Similar to the else, the elev statement is optional.



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However, unlike Alt for which there can be at most one statement, there can be an arbitrary number



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of Ayliffe statements following in.



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If so, I'll show you how it works.



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So we'll create a variable named model and ask for the value to be entered by the user.



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If model equals one print, youchoose Rolls Royce.



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Ayliffe model equals to.



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Print you choose Aston Martin.



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Live model equals three.



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You choose Bentley.



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Else print invalid number.



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And what do we see here?



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If the user entered value is one to three.



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And the program will return us a value of one to three.



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If it is not, and the program will return as an invalid number.



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So there's no need to use an LST pattern in the programs.



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Our code will work without the else block.



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However, if an incorrect action is entered in this case, we will see that nothing is written on the



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screen.



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So using the else block is entirely optional.



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It's up to us.



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But you can see how useful it is.



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So let's write the previous example again without the URL statement and see what happens.



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So as you can see, if the user entered value is in the range between one, two, three, then the program



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will return us the value of one to three.



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If it is not, then the program will return is nothing.



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So using the old block is entirely up to you.



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One more thing left Bloche cannot be written unless the if condition is written.



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Doing so will cause an error in Python.



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Let me show you what that looks like.



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All right, so in this lesson, we have learned the basic things we need to know about conditional statements.



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Our next lesson, we're going to try to learn the loop concept in Python.



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You'll see why reserved it to be separate.



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All right.



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I'll see you in the next lesson.



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Until then, have a nice day.