Difference between revisions of "Rust/C2/Control-Flow-in-Rust/English"

Learning Objectives

• if/else control flow statements
• Different types of loops supported in Rust
• Syntax of all the control flow statements and their usage

• Ubuntu Linux OS version 18.04
• Rust version 1.47.0
• Visual Studio Code version 1.45.0 (code editor)

However, you may use any other editor of your choice.

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

• The file used in this tutorial is available in the Code files link on this tutorial page.
• Pls download and extract the file.
• Make a copy and then use it for practising.

• Control flow means deciding whether to run a piece of code, based on a condition.
• This is an integral part of any programming language.
• This can be achieved using if and else statements

[Highlight]: if expressions

• if is the most common way to handle the flow of our code.

[Highlight]: else if

• We can use else if, if there are multiple conditions to be evaluated.

• We can use if without else, however else cannot be used without if.
• else is always preceded with an if statement.

• Also, we can use one or more else if along with the if statement.
• Ensure that when you use else if, always follow it up with an else condition too.
• The code works fine even when we don’t end with an else statement.
• However, to maintain coding standards it is advised to use else condition when we are using else if

Let us understand all this by using an example.

Ensure that you have root permissions to run the commands.

cd Desktop/MyRustProject

[Enter]

cargo new control_flow

[Enter]

Type the command as shown.

I will use Visual Studio Code editor for this demonstration.

Welcome Page ->

Open Folder ->

control_flow

Browse and locate the folder “control_flow”.

Then click on the OK button at the top right corner.

Click on control_flow

fn main(){

let a = 30;

let b = 20;

if a>b{

println!(“A is greater than B”);

} else {

println!(“B is greater than A”);

}

}

If a>b

println!(“A is greater than B”);

else {

println!(“B is greater than A”);

}

cd control_flow[Enter]

cargo run [Enter]

A is greater than B

fn main(){

let marks = 50;

if marks>35{

println!(“You are qualified!”);

}

}

if(marks>35){

println!(“You are qualified!”);

}

When the condition gets satisfied, the block gets executed.

If not, then nothing is printed.

cargo run [Enter]

You are qualified!

Here, we emphasise that only an if condition can exist without an else statement.

fn main(){

let a = 5;

if a%2 == 0{

println!(“Number is divisible by 2”);

} else if a%3 == 0{

println!(“Number is divisible by 3”);

} else {

println!(“Number is not divisible by 2 and 3”);

}

}

This is the if - else if - else statement.

if a%2 == 0{

println!(“Number is divisible by 2”);

}

When this condition is satisfied, the if block gets executed.

When this condition fails, the else if block is checked.

else if a%3 == 0{

println!(“Number is divisible by 3”);

}

When this condition is satisfied, the else if block gets executed.

else {

println!(“Number is not divisible by 2 and 3”);

}

And prints this message as the above two conditions are not satisfied.

cargo run [Enter]

Number is not divisible by 2 and 3

• Loops are control structures that are repeatedly executed until a particular condition fails.
• That means, loops repeat a block of code n number of times until a particular condition fails.

• There are two types of loops supported in Rust
  • For loop and
  • While loop
• Note: There is no do while loop in Rust

fn main(){

loop {

println!(“Hello World!”);

}

}

loop

cargo run [Enter]

Hello world

(being printed infinite times)

This is an infinite loop.

loop {

println!(“Hello, World!”);

break;

}

break;

cargo run [Enter]

Hello, World!

This is because the loop breaks after one execution.

We can even have a condition check and break whenever the condition fails.

Next, let us learn about while loop.

fn main(){

let mut a = 3;

while a!=0 {

println!(“{}”,a);

a = a - 1;

}

}

let mut a = 3;

while a!=0 {

While keyword is followed by the condition a not equal to zero.

Until and unless the condition returns false, the block gets executed.

println!(“{}”,a);

a = a - 1;

cargo run [Enter]

3

2

1

Only when the value of a is zero the condition returns false and the block will stop getting executed.

So 0 is not printed.

fn main(){

let arr = [2,3,5,7,11];

for value in arr.iter() {

println!(“Value = {}”,value);

}

}

let arr = [2,3,5,7,11];

for value in arr.iter() {

In the first iteration, the value will be 2.

And in the second iteration, the value will be 3 and so on.

Notify:

https://doc.rust-lang.org/std/iter/index.html

Here, we are using iter() method which iterates over the address of T.

For more details, on iter method refer to the link.

In our example, The iter() method will iterate over all the values in the array.

println!(“Value = {}”,value);

cargo run [Enter]

Value = 2

Value = 3

Value = 5

Value = 7

Value = 11

We can see the for loop has been executed once for each and every element in the array.

And on reaching the end of the array, the for loop stopped executing.

Let’s summarize.

• if/else control flow statements
• Different types of loops and
• Their syntax and usage

• Go to the project folder rust-assignment
• In the main.rs file
  • Create a array named n and assign 10 random numbers to it
  • Loop over the array and
  • Count the number of even values and odd values
  • Print the count of odd and even values
• Compile and execute the project.
• Observe the output in the Terminal

• The video at the following link summarises the Spoken Tutorial project.
• Please download and watch it

• We conduct workshops using spoken tutorials and give certificates.
• For more details, please write to us.