format! Macro

Part of the Fundamentals section of Coddy's Rust journey — lesson 70 of 75.

In Rust, the format! macro allows you to combine text with variables in a readable and customizable way. This macro is similar to println!, but instead of printing the output to the console, it returns a formatted string that you can store in a variable or use in other operations.

The simplest syntax uses unnamed placeholders {}:

let name = "Alice";
let age = 30;

let formatted = format!("Name: {}, Age: {}", name, age);
println!("{}", formatted);
// Output: Name: Alice, Age: 30

You can use variable names directly in the placeholders:

let name = "Bob";
let age = 25;

let formatted = format!("Name: {name}, Age: {age}");
println!("{}", formatted);
// Output: Name: Bob, Age: 25

You can specify the position of arguments using numbers:

let formatted = format!("{1} {0} {2}", "first", "second", "third");
println!("{}", formatted);
// Output: second first third

You can control how values are formatted using format specifiers:

// Number formatting
let pi = 3.1415926;
let formatted_float = format!("{:.2}", pi);
// "3.14"

// Padding with zeros
let padded = format!("{:0>5}", "123");
// "00123"

Challenge

Easy

Create a program that generates a secret code from a name and birth year using these exact rules:

Takes the first letter of the name and makes it uppercase
Reverses the year digits
Wraps the first letter with "⭐" symbols
Adds a "-" between the wrapped letter and reversed year

To reverse a string use the following code: .to_string().chars().rev().collect::<String>()

Cheat sheet

The format! macro combines text with variables and returns a formatted string that can be stored in a variable.

Basic syntax with unnamed placeholders:

let name = "Alice";
let age = 30;
let formatted = format!("Name: {}, Age: {}", name, age);

Using variable names directly in placeholders:

let name = "Bob";
let age = 25;
let formatted = format!("Name: {name}, Age: {age}");

Specifying argument positions with numbers:

let formatted = format!("{1} {0} {2}", "first", "second", "third");
// Output: "second first third"

Format specifiers for controlling output:

// Number formatting
let pi = 3.1415926;
let formatted_float = format!("{:.2}", pi); // "3.14"

// Padding with zeros
let padded = format!("{:0>5}", "123"); // "00123"

To reverse a string: .to_string().chars().rev().collect::<String>()

Try it yourself

use std::io;


fn main() {
    let mut input_name = String::new();
    let mut input_year = String::new();
    io::stdin().read_line(&mut input_name).unwrap();
    io::stdin().read_line(&mut input_year).unwrap();
    let name = input_name.trim();
    let year: i32 = input_year.trim().parse().unwrap();

    // Write your code below
    
    
    let secret_code =
    println!("{}", secret_code);
}