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Welcome back again in the course. We will

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complete our discussion of the if statement

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in this tutorial, by learning the remainder of

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its variants. So, let's get started.

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The first variant of the basic if statement we

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will learn is, the nested if statement. By

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nested, we mean an if statement which contains

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another if statement inside it. Let us see

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the general syntax for the nested if variant.

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The outer conditions are being checked first,

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if it happens to be true, then the statement

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included inside it's respective body will get

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a chance to execute. When both the outer and

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inner conditions are true, then the statement

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inside the inner if statement will also get a

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chance to execute. Please note that the outer

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and inner if statements may have the

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respective else part also.

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Let us do a quick example

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on this, where we will take an input

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from the user, which will be checked for being

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zero or not. If it is not zero, then we will

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check if it is being odd or even. We will

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assume that the number zero is neither odd

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nor even. Let us code this problem.

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Next I will add a suitable display message, so

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that the user knows what the program is

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expecting as an input.

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First we will take an integer input from the user.

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Next we will check if the value is zero or

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not, using an if statement.

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The same statement may be written as not,

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and then some_num == 0.

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Inside the body of the if statement, I

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will add additional conditions

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to check if the number is even or odd.

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The percent operator is also called as mod

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operator, and it computes the remainder

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after dividing the number mentioned to the

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left of it, by the number mentioned to the

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right of it. In this case, it will divide the

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value of some_num by 2, and will

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compute the remainder. If the remainder

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happens to have a value of 0, then it will

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be an indication that the number is even, and

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if the remainder is not zero then the number

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will be odd. If the outer if condition is

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true, the inner if condition will be checked.

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Based on whether the associated inner if

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condition is true or not, we will either

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execute the inner if or, or its associated else parts.

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For the outer if statement, we may have

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an optional else part also. We may add a

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suitable print statement to the else part to

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indicate that the number is 0, and it is

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therefore neither even or odd.

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Let us cargo run this.

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I will provide a value of 13, it

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displays that the number is odd, okay great.

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It is a good programming practice to

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properly indent the inner if statement

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and its respective body, so that the code is

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easily readable. Let us now learn the if let

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syntax variant of the if statement.

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With the help of this variant, we are able to assign a

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value to some variable based on the body of

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the if statement. Let us look at the

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general syntax first.

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Inside the body of the if and the else parts,

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we need to have a single value or statement,

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after which there is no semicolon, which will

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be the value that will be assigned to the

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variable_name variable. Finally,

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we will need to put a semicolon at the end of

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the complete block of the if else statements.

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Let us look at this variant in action.

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I will declare a variable, a value, which will store

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the result of the if else statement.

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The condition associated with the if statement, in this case

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is true, which means that the body of the if

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statement will be executed. And therefore the

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value 1 will be assigned to the variable value,

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let us execute this.

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The value is being displayed

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for the variable. Please note

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that the return value from the if part is

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without a semicolon, and the value returned

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from the else part is also without a

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semicolon, and both of these values are of the same type.

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One of these values will be

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assigned to the variable value, and we know

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that a variable in Rust should have a defined

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type at compile time, otherwise the compiler

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will complain. If for instance, we change the

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value of 2 in the else part to that of 2.0

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and save. So the compiler will rightfully

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complain, because it will be confused

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regarding the data type of the variable value.

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Now, let us look at another scenario,

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or variant of the if let syntax. We can use the

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same syntax in the if-else ladder, that we

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have seen in the previous tutorial.

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Let us see how to use if let variant in the

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context of if-else ladder.

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We will use the same program

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that we saw in the previous tutorial,

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and we will modify it.

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Instead of rewriting it, I will paste it.

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[No Audio]

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Now instead of assigning and setting the

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value of the variable grade, inside each of

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the blocks, I will assign it using the

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if let syntax by declaring the grade

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variable at the start and then I will mention

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all the conditions.

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Inside each of the block, I

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will remove the assignment and we'll just

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keep the character letters.

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Let us do the remaining necessary changes.

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You may note, let the code is now more

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reduced and therefore more readable and compact.

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Please note that, since we need to

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make an assignment to the variable, so we

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cannot skip the else part in this case,

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because, that will leave the variable empty.

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The point to remember is that, with the

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if let syntax, we cannot leave a variable empty.

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Finally we also need to put the

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mandatory semicolon.

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[No Audio]

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Okay let us execute.

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[No Audio]

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You may note, that the variable has been

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assigned a value, based on the marks of the student.

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The important point to note is that,

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we should have at least one block which

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returns some value for the variable.

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With this we end this tutorial, we have learned

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additional two ways in which the if statement

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can be used, that is the nested if and the if let syntax.

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In the upcoming tutorial, we will

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be looking at a very similar but different

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construct called match. Which will also work

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very similarly, but has some essential differences also.

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Do come back for covering that

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and until next tutorial, enjoy Rust programming.

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[No Audio]