Difference between revisions of "Rust-Programming-Language/C2/Functions-and-Control-Flow/English"

Learning Objectives

• Control Flow Statement and
• Functions

System Requirements

• Ubuntu Linux OS version 22.04
• Rust 1.80.0
• Visual Studio Code 1.19.0

Prerequisites

• You should be familiar with compiling and running Rust files
• If not go through the prerequisite Rust tutorial on this website

Code Files

• The files used in this tutorial are provided in the Code files link of this tutorial page
• Please download and extract the files.
• Make a copy and then use them while practicing.

Conditional Statements

• if
• else if
• else

statements for making decisions based on conditions.

It always returns a boolean value.

We can see a terminal window at the bottom.

> cargo new functions

Type the command cargo new functions and press Enter

Open the created project as shown.

let n = 100; if n>100{ println!("Greater than 100"); }else if n==100{ println!("Equal to 100"); }else { println!("Smaller than 100"); }

}

If n is greater than 100, it prints a “greater than 100” statement.

If n equals 100, the second print statement will be executed.

If n is less than 100, it prints “smaller than 100”.

You can include multiple else if statements to check multiple conditions in sequence.

The condition must be true to run the code wrapped to it.

Press Ctrl and S to save the file.

Now let us run the program.

The output shows “equal to 100” as we have assigned n as 100 in the program.

Loop

• A loop is used to repeat a block of code until the specified condition is met
• The loop keyword creates an infinite loop unless you explicitly break out of it
• Rust provides several ways to loop, including loop, while, and for

Clear the code window and replace the code from the code file as shown.

let mut count = 0; loop { count += 1; println!("Count: {}", count); if count == 5 { break; } } }

A loop is created in which it increases the count variable by 1.

It prints the value of count in the current iteration.

It will also check for the if statement condition.

When the variable count will be equal to 5, it will stop executing and come out of the loop.

If there is no if statement, it will execute infinitely.

Press Ctrl and S to save the file.

Let us run the program

We can see the count variable is printed from 1 to 5.

It stops executing when the count reaches 5.

Replace the code from the Code file with the while loop program.

let mut counter = 1; // usage of while loop while counter < 6 { println!("{}", counter); counter += 1; } }

Here, the loop keeps running till the counter variable is less than 6.

Inside the loop, we are increasing the value of the counter by 1.

After the 5th iteration, the value of the counter will be 6.

So the condition, counter is less than 6 becomes false and the loop is terminated.

Save the program.

Check the output.

For loop

• The for loop iterates over a range or a collection
• An iterator which provides a way to access elements one at a time.
• In a For loop, many collections like arrays, vectors, and ranges, implement the Iterator

For loop -example

fn main() { for n in 0..11 { println!("{}", n); } }

A range with two dots like 0..11 is inclusive on the left.

That is, it starts at 0 and exclusive on the right that is, ends at 10.

This program will print numbers from 0 to 10.

Clear the code window and copy and paste the code from the code file.

let data = [2, 1, 17, 99, 34, 56]; // iterator //let numbers_iterator = data.iter(); for i in data.iter(){ println!("{}", i); } }

The data.iter() method creates an iterator for the array data.

The for loop takes each element produced by the iterator and binds it to the variable data.

Inside the for loop, println is used to print the value of each element.

Save the file.

Let us execute the program.

We can see the array elements are printed in sequence.

Let us see how to use a reverse method in the for loop.

for i in (1..=11).rev() { println!("{i}..."); } println!("Launch!"); }

If we want the range to include 11 as well, we can write it as (1..=11).

This is known as an inclusive range.

The rev() method is applied to the range to produce a reverse iterator.

This means the numbers will be fetched in reverse order.

Save the file.

Let us check the output.

We can see the output displayed in the reverse order as expected.

for i in (1..11).rev() { if i % 2 == 0 { continue; } println!("{i}..."); } println!("Launch!"); }

The if statement checks if i is divisible by 2.

If this condition is true, the continue statement is executed.

The continue statement skips the rest of the loop body for the current iteration and moves to the next one.

Save the program.

We can see the odd numbers are printed between 11 and 1.

Functions

• It is a set of statements to perform a specific task.
• Functions organize the program into logical blocks of code.
• Functions make the code reusable.
• It structures your programs and makes them more readable and maintainable.

Function - Example // define a function fn greet() { println!("Hello, World!"); } fn main() { //function call greet(); }

To invoke the created function, we need to make a function call.

Notice that we are calling the function from inside main().

In Rust, main() is also a function known as a built-in function that has a special meaning.

In the main.rs file, replace the code from the code file.

fn add(a: i32, b: i32) { let sum = a + b; println!("Sum of a and b = {}", sum); } fn main() { // call add function with arguments add(12, 10); }

Here, a and b are function parameters.

i32 is the data type of parameters.

12 and 10 are known as function arguments that are passed to the add function.

That means 12 is assigned to a and 10 is assigned to b.

Save the file.

It prints the sum of a and b as 22.

Replace the code as shown.

   length * breadth

}

fn main() {

    let k = area(5, 6);

    println!("Area of the rectangle = {k}");

}

Change the program to return length*breadth

The area function takes two parameters, length and breadth, both of type i32.

-> i32 - right arrow i32 before the opening curly bracket indicates the function's return type.

It returns an i32 value representing the area of the rectangle.

In the next line, notice the lack of a semicolon after length * breadth.

In Rust, the absence of a semicolon signifies that this line is an expression.

The result value is returned by the function.

Save the file and run the program.

We can see the output as the area of the rectangle is 30.

Now let us add a semicolon at the end of length into Breadth statement.

Let us run the program and see how the program works.

It would not return a value and cause a compilation error.

This time we get an error, remove this semicolon to return this value.

This is because it is being considered as a statement and not as a return value.

You can use either conventions 

• length*breadth without semicolon or
• return length*breadth with semicolon

for returning the value.

Save the file and run the program.

We can observe that the area of the rectangle is 30.

Let us summarize.

Summary

• Control Flow Statement and
• Functions

Assignment

• In the main.rs file
  • Create a function that accepts a number as a parameter
  • Print EVEN if the number is even
  • Else print ODD
• Compile and execute the project.
• Observe the output in the Terminal

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Acknowledgement

Acknowledgement

Thank You

Thank you for joining.