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[No audio]

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This section is about basic programming with Rust.

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If you are already familiar with some other

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programming language, then this section will give you

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a quick start for writing codes in Rust.

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You don't need to worry if you are new

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as we will explain everything in detail and will

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learn everything in a step by step fashion from

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complete scratch. In this very first tutorial,

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in this section, we will learn two things.

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That is comments and basic print commands.

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So without any delay, let's get started.

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Almost every programming language support

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the use of comments.

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A comment is a programmer readable, explanation or annotation

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in the source code file of a computer program

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and they are written with the intention of making

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the source code easier to understand.

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They are ignored by compilers and are not executed.

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Commented code lines in Rust files are

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lines that starts with two backslashes.

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For instance, this line is going

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to be treated as comments.

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[No audio]

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We can have more comments in the code by adding

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more lines that starts with a couple of backslashes.

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[No audio]

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There are situations in which we may

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want to add multiple lines of comments.

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In that situation, it is not very convenient

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and effective to keep on adding backslashes at

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the start of each and every line.

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An efficient way of writing multiline comments in Rust

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is with the help of backslash and star.

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The comment is ended with the

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help of star followed by backslash.

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Let us add a single multiline comment.

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[No audio]

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These two types of comments are enough for now

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to add necessary documentation and explanation to our code.

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We will now cover the second topic of

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the lecture which is to learn the basic

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print command and some of its variants.

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We have already seen the basic print command

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in our first Rust program of Hello World.

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It is used to print something through the terminal.

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Let me add a simple print statement for

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printing the text of Hello from Rust.

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[No audio]

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Please note that ideally you should put semicolons

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after the end of each line of code.

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Of course, there are some exceptions which will become

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evident to us as we progress along the course.

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The ln after the print means that after

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this command, any subsequent printing to the terminal

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will be on the next line.

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The exclamation mark is a symbol

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to denote a Rust macro.

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In simple words, a macro are a

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way of writing code that writes other

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code which is also known as metaprogramming.

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The Rust macros are substituted by other

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code before the program is being executed.

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Don't worry about them for now as they will make

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sense as we progress along the course and cover the

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topic of macros in the later on sections.

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For now, it is sufficient to know that it is a macro.

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To execute the code, we will typically use the cargo

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run command by typing cargo run in the terminal.

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This command will execute the program and any output

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from the program will be displayed on the terminal.

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[No audio]

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Comments may be inserted within

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a Rust statement or command.

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It is done with the help of syntax

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that we use to write multiline comments.

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For instance, consider the Hello World print statement

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again. We can command a piece of this statement to

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be treated as comment and not part of the source

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code by enclosing it inside the multiline comment.

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The ln in this case will be treated as comment.

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Unlike println command, which moves to the next line

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after printing to the terminal, the print does not move

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to the next line after printing to the terminal.

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Let us now learn how to print strings and numbers.

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[No audio]

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We cannot print strings or numbers by

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just enclosing it inside the print statement.

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It will generate an error message.

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This is a nice feature of Rust

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which is known as compile time errors.

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The compile time errors refers to the

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error messages that are indicated by the

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compiler before we even run the program.

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If I move my mouse cursor, it will

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give me more details about the error message.

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In this case, it says you might

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be missing a string literal to format.

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If for some reason I do not understand the details

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that are being provided by the compiler, so I may

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execute this program and it will give me more information.

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[No audio]

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In this case, it is giving me the

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correct syntax indicated by the green text.

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Let us explain the problem

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in this case. The print function needs

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some sort of placeholder inside the double

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quotes which will be replaced using the

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constants, strings, variables or whatever we mention.

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So the correct syntax for printing out the value

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of ten will be placeholder inside the double quotes.

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Let me add some suitable text

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also. During the execution, the placeholder will be

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replaced with the value that we have mentioned.

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The output in this case will be the

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value is ten. If there are multiple placeholders

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and multiple values after the double quotes,

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so the placeholder will be replaced in the

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order in which the parameters are being provided.

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The order is always going to be from left to right.

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Let us look at printing the strings now.

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Strings are indicated with the help of double quotes.

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Let us add a print statement for

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printing my first name and last name

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which are being provided as string arguments.

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[No audio]

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This statement will print, My first name is

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Nouman and my last name is Azam.

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The first placeholder was being replaced with the first

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parameter after the double quotes and the second placeholder

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has been replaced with the second parameter.

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To print text on the same line and not on a

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new line, we will use the print statement without the ln.

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Let me add a print statement.

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[No audio]

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This text will now be printed on the same line.

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Please note that the print will only occur

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on the next line when there is no

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more spaces to print on the same line.

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Let me add some printing statements to see this.

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[No audio]

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Let us now look at another

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print statement. In this case

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now we have inserted text inside the print

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statement which is spanning more than one line.

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We also have a print statement with no

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text which will ensure that subsequent printing will

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be performed on the next line.

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Let us see the output in this case.

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[No audio]

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You may note that the output

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is also spanning multiple lines,

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although we have used this simple print statement.

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The key point here is that the print or println will

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print what it is instructed to print, and

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when the printing is complete, the println command will

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print subsequent text on next line, while the simple print

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will print subsequent printing on the same line.

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We will now look at the use of escape sequences.

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[No audio]

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An escape sequence contains a backslash symbol followed

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by one of the escape sequence characters.

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It is a combination of characters that has a

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meaning other than the literal character contained therein.

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We will cover a few of the most important ones.

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The first one in this regards is the backslash

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n, which is used to ensure that subsequent printing

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will be done on the next line.

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Adding it two times will mean that one line

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will be empty and will contain no text.

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Let me add some text also.

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[No audio]

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Let us confirm the output now.

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[No audio]

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There are other escape sequences also such as

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slash t, which is for inserting a tab.

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A tab is essentially spaces of some fixed length.

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Let us use it inside a print statement with some text.

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[No audio]

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Let us see the output now.

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[No audio]

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You may note some empty spaces at the

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beginning of the output on the terminal.

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Let us see one more frequently used escape sequence.

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The slash r is used for carriage return, which

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has its history related to the typewriter which people

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used in the old days for typing out documents.

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A carriage return moves your carriage all the way

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to the right at the start of the line.

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So anything that you print afterwards will delete any

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previous text that is present on the same line.

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Let me add a print statement with some

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text and the carriage return escape sequence.

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[No audio]

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The Rust will first print the text

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before the slash r on the screen.

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When it encounters slash r, it will move to the beginning

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of the same line and will write the remaining text after

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the slash r in the print command on the screen.

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This will erase the previously

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written text on the screen.

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Let us see the output of this.

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[No audio]

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We may note that we are only able to see the text

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of, this text will only appear on the screen, and we are

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unable to see the first part of the text on the terminal.

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A backslash is very useful when

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used inside the print statement.

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It is used to ignore the effect

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of one escape sequence which comes afterwards

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and will print it as ordinary text.

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For instance, let us add a couple of slash

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n inside a print statement with some text.

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[No audio]

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The first slash n has

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an additional backslash before it.

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This will ignore its special meaning and therefore the first

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slash n will be part of the text, while the

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second slash n will have its special meaning.

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Let us see the output.

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[No audio]

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The next use of the backslash is to display

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single quotes and double quotes inside the print statement.

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Let me add a print statement to explain this.

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[No audio]

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In this print statement, a single quote will

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be displayed in place of the backslash quote,

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while a double quote will be displayed in

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place of the backslash double quote.

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The double quotes in this case will not be

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treated as the ending double quotes corresponding to the

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starting double quotes of the print statement.

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Let us see its output.

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The backslash special meaning can be used to

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print the backslash itself inside the print statement.

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We will use two backslashes in this case.

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Let me add a print statement to illustrate this.

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[No audio]

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In this example now, the first backslash will ignore the

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special meaning of the second backslash and

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therefore the second backslash will be printed.

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One of the main uses of the backslash where

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it will be used as part of the printing

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text is to display the directory or folder locations.

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Next we will look at the positional arguments.

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The positional arguments are a list of parameters

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or arguments that we pass to the print

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command after the double quote separated by commas.

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Let me add a print text with some positional arguments.

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[No audio]

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In this statement, the numbers inside the placeholder

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will be replaced by the respective parameters.

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The first parameter, which is the string of like,

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will be replaced by the placeholder containing one.

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The second parameter, which has the value of

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20, will be replaced by the placeholder containing

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the value of two, and in the same

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way the third parameter will also be replaced.

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Let us see the respective outputs.

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[No audio]

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Sometimes it may be more meaningful

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to use names instead of numbers.

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This means that we will use the names of the

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arguments instead of using their numbers inside the placeholders.

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Let us look at an example by including a

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suitable print statement containing a couple of named arguments.

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[No audio]

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The first placeholder will contain the value of

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the parameter with the name of language and

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the second parameter will contain the value of

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the parameter with the name of activity.

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The order does not matter in this case.

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Let us look at one last topic and that

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is printing basic Math inside a print statement.

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I will add a print statement in this case

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which will print the value of some addition.

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The placeholder in this example will be

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replaced with the value of addition operation.

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There are a whole bunch of other details which we

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will only cover when they become relevant to us

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in the course. We will be covering

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basic data types in the next lecture,

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so do come back for learning that,

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and until then, happy Rust programming.

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