a3.hello-world.md

title	slug
Hello World	hello-world

Hello, World!

fn main() {
    println!("Hello, world!");
}

fn means function. The main function is the beginning of every Rust program. println!() prints text to the console and its ! indicates that it’s a macro rather than a function.

💡 Rust files should have .rs file extension and if you’re using more than one word for the file name, follow the snake_case convention.

• Save the above code in file.rs , but it can be any name with .rs extension.
• Compile it with rustc file.rs
• Execute it with ./file on Linux and Mac or file.exe on Windows

Rust Playground

Rust Playground is a web interface for running Rust code.

👨‍🏫 Before going to the next...

• These are the other usages of the println!() macro,

  println!("{}, {}!", "Hello", "world"); // Hello, world!
  
  println!("{0}, {1}!", "Hello", "world"); // Hello, world!
  
  println!("{a}, {b}!", a = "Hello", b = "world"); // Hello, world!
  
  let (a, b) = ("Hello", "world"); // 💡 Two Variable bindings declare & initialize in one line.
  println!("{a}, {b}!"); // Hello, world!
  
  println!(); // A new line

  // Debug print and pretty-print debug print format specifiers
  println!("{:?}", [1, 2, 3]); // [1, 2, 3]
  
  println!("{:#?}", [1, 2, 3]);
  /*
      [
          1,
          2,
          3
      ]
  */
  
  // 💡 We can use the variable directly with the format specifier as well.
  let a = [1, 2, 3];
  
  println!("{a:?}"); // similar to println!("{:?}", a);
  println!("{a:#?}"); // similar to println!("{:#?}", a);

• Rust has a print!() macro as well.

  print!("Hello, world!\n"); // With new line
  print!("Hello, world!"); // Without new line

• The format!() macro is used to store the formatted string.

  let a = format!("{}, {}!", "Hello", "world");
  println!("{a}"); // Hello, world!

• Let's play a bit more...

  println!("{}", "Hello, world!".to_uppercase()); // HELLO, WORLD!
  println!("{}", "Hello, world!".to_lowercase()); // hello, world!
  
  println!("{}", "⭐️".repeat(3)); // ⭐️⭐️⭐️
  
  println!("{}", "Hello, world!".chars().count()); // 13
  // 💡 For more accurate results, you should use a crate like unicode_segmentation that follows more accurate Unicode text segmentation standards.

• Different format specifiers.

  let a = 255;
  println!("{a}"); // 255
  
  println!("{a:b}"); // Binary 💡 11111111
  println!("{a:o}"); // Octal 💡 377
  println!("{a:x}"); // LowerHex 💡 ff
  println!("{a:X}"); // UpperHex 💡 FF
  
  println!("{a:0>5}"); // Add leading zeros till character lengh 5 💡 00255
  println!("{a:0<5}"); // Add tailing zeros till character lengh 5 💡 25500

• Check the difference between macros and functions.

• For more rustc commands, check the rustc --help command.