🦀 Rust – Hello World Example: Your First Rust Program Explained

🧲 Introduction – Why Start with Hello World?

The best way to begin learning any programming language is by writing a simple “Hello, World!” program. In Rust, this not only teaches you the basic syntax but also introduces core concepts like functions, macros, and compilation flow.

🎯 In this guide, you’ll learn:

• How to write, compile, and run your first Rust program
• The role of the main function and println! macro
• Project structure using cargo
• How Rust’s compilation produces executables

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📝 Writing a Basic Hello World Program

Here’s the simplest Rust program you can write:

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

🔍 Explanation Line-by-Line:

Code	Meaning
fn main()	Defines the entry point of the program (like main() in C/C++)
{}	Denotes the body of the function
println!("...")	A macro that prints to standard output
! after println	Indicates it’s a macro, not a function

📤 Output:

Hello, Rustaceans!

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🔧 Compile and Run with rustc

If you’re using raw Rust tools without cargo, save the code to a file named hello.rs.

📦 Step-by-step (manual):

rustc hello.rs
./hello      # or hello.exe on Windows

✅ This creates an executable named hello that you can run directly.

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🚀 Creating a Hello World Project with Cargo

cargo is the preferred way to manage Rust projects.

🛠️ Step 1: Create a new project

cargo new hello_project
cd hello_project

This generates:

hello_project/
├── Cargo.toml       # Project metadata & dependencies
└── src/
    └── main.rs      # Default entry point

📜 Step 2: Code in src/main.rs

fn main() {
    println!("Hello from Cargo!");
}

▶️ Step 3: Run the program

cargo run

📤 Output:

   Compiling hello_project v0.1.0
    Finished dev [unoptimized + debuginfo] target(s)
     Running `target/debug/hello_project`
Hello from Cargo!

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📚 println! Macro Variations

fn main() {
    println!("Rust");                          // Basic string
    println!("{} {}", "Hello", "Rust");        // Format with {}
    println!("Sum is: {}", 5 + 10);            // Expression output
}

📤 Output:

Rust
Hello Rust
Sum is: 15

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⚠️ Common Beginner Mistakes

Mistake	Error Message / Issue	Fix
Missing ! in println	expected function, found macro	Use println! not println
Misspelling main	can’t find function Main	Always use lowercase fn main()
Forgetting semicolon	unexpected token	End expressions with ; when needed

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🧪 Run Rust Code Online

Try Rust in your browser without installing anything:

🔗 https://play.rust-lang.org

Paste your Hello World code, hit Run, and see the output instantly.

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📌 Summary – Recap & Next Steps

Your first Rust program is more than just a greeting—it teaches you syntax, compilation, and core structure. From here, you’re ready to explore variables, data types, and control flow.

🔍 Key Takeaways:

• main() is the starting point for Rust programs
• println! is a macro used to print messages to the console
• Use cargo for real-world projects and easier workflow
• Rust compiles to native executables

⚙️ Move on to learning variables, constants, and data types in Rust – Variables.

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❓FAQs

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❓ Why does Rust use println! instead of print()?
✅ Rust uses macros (like println!) for compile-time code generation. The ! denotes a macro, not a regular function.

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❓ Can I run Rust code without installing Rust?
✅ Yes, use play.rust-lang.org or TutorialsPoint Rust compiler for online execution.

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❓ Do I need cargo to write Rust programs?
✅ No, but cargo simplifies project creation, building, and dependency management. It’s recommended for all but the smallest examples.

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❓ What does rustc do?
✅ rustc is the Rust compiler. It compiles .rs source files into native executables.

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