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The Basic Program

• Rust code is always put in a file with .rs extension.
• Every executable Rust program starts execution from the main function.

fn main() {
    println!("Hello World!");
}

println! prints text to standard output and automatically adds a newline at the end.

• println! is a macro not a function.
• Macros are evaluated at compile time.

Example 2:

Rust does not use string interpolation like Python or JavaScript. Instead, it uses format placeholders inside the string.

fn main() {
    println!("Number: {}", 1);
}

{} is a placeholder.

Printing variables

fn main() {
    let age = 25;
    println!("Age: {}", age);
}

Positional Arguments

Arguments are filled in same order.

fn main() {
    println!("{} last name is {}", "Rachel", "Green");
}

Named Arguments

Helps in code readability.

fn main() {
    println!("{fname} last name is {lname}", fname="Rachel", lname="Green");
}

This is different from string interpolation in python.

Using Expressions

fn main() {
    println!("{} * {} = {}", 15, 15, 15 * 15);
}

Number Formatting

Rust supports multiple number representations using format specifiers

fn main() {
    println!(
        "Decimal: {}\nBinary: {:b}\nHex: {:x}\nOctal: {:o}",
        20, 20, 20, 20
    );
}

Debug Printing {:?}

fn main() {
    println!("{:?}", (100, "Rachel Green"));
}

fn main() {
    println!("{}{:?}", "Rachel Green", "Rachel Green"));
}

Debug printing it for debugging, not for user facing outputs.

We will discuss about Debug Trait in later weeks.

#println #macro #trait #debug #placeholderVer 2.0.8