Rust Tutorial : Package Manager
from tutorialspoint.com

Cargo
Cargo is the package manager for RUST
acts as a tool and manages Rust projects
commonly used cargo commands

  • cargo build - compiles the current project
  • cargo check - analyzes the current project and report errors, but doesn't build object files
  • cargo run - builds and executes src/main.rs
  • cargo clean - removes the target directory
  • cargo update - updates dependencies listed in Cargo.lock
  • cargo new - creates a new cargo project
Cargo helps to download third party libraries
acts like a package manager
can also build own libraries
Cargo is installed by default when Rust is installed
to check Cargo version 
cargo --version

to create a new cargo project use the commands below

create a binary crate
cargo new project_name --bin
create a library crate
cargo new project_name --lib
Create a Binary Cargo project
Create a Binary Cargo project
game generates a random number and prompts the user to guess the number

Create a project folder
in a terminal and enter the following command 
cargo new guess-game-app --bin
creates a new folder structure 
guess-game-app/
    Cargo.toml
    src/
        main.rs
public crates are stored in a central repository called crates.io

Include references to external libraries
example needs to generate a random number
standard library does not provide random number generation logic
need to look at external libraries or crates
use rand crate which is available at crates.io

rand is a rust library for random number generation
rand provides

  • utilities to generate random numbers
  • to convert them to useful types and distributions
  • some randomness-related algorithms
crates.io provides two ways to add the rand package to the project
  1. from the console run 
    cargo add rand
  2. add the following line to Cargo.toml 
    rand = "0.9.0"
the first way lets cargo edit Cargo.toml using the current version of the crate

Compile the Project
in the console navigate to the project folder
execute the command 
cargo build
the output will be similar to 
Updating registry `https://github.com/rust-lang/crates.io-index`
Downloading rand v0.9.0
Downloading rand_core v0.2.2
Downloading winapi v0.3.6
Downloading rand_core v0.3.0
   Compiling winapi v0.3.6
   Compiling rand_core v0.3.0
   Compiling rand_core v0.2.2
   Compiling rand v0.5.5
   Compiling guess-game-app v0.1.0 
   (file:///d:/rust/guess-game-app)
   Finished dev [unoptimized + debuginfo] target(s) in 1.08s
the rand crate and all transitive dependencies (inner dependencies of rand) will be automatically downloaded

Understanding the Business Logic
the logic is simple so the code should be simple
  1. game initially generates a random number
  2. user is asked to enter input and guess the number
  3. if number is less than the generated number, a message 'Too low' is printed.
  4. if number is greater than the generated number, a message 'Too high' is printed
  5. if the user enters the number generated by the program, the game exits
Edit the main.rs file
replace the default code with the code below 
use std::io;
extern crate rand; 
//importing external crate
use rand::random;
fn get_guess() -> u8 {
   loop {
      println!("Input guess") ;
      let mut guess = String::new();
      io::stdin().read_line(&mut guess).expect("could not read from stdin");
      match guess.trim().parse::(){ 
         // remember to trim input to avoid enter spaces
         Ok(v) => return v,
         Err(e) => println!("could not understand input {}",e)
      }
   }
}
fn handle_guess(guess:u8,correct:u8)-> bool {
   if guess < correct {
      println!("Too low");
      false
   } else if guess> correct {
      println!("Too high");
      false
   } else {
      println!("You go it ..");
      true
   }
}
fn main() {
   println!("Welcome to no guessing game");
   let correct:u8 = random();
   println!("correct value is {}",correct);
   loop {
      let guess = get_guess();
      if handle_guess(guess,correct){
         break;
      }
   }
}
Compile and Execute the Project
from the project directory in the console run the command 
cargo run
output 
Welcome to no guessing game
correct value is 97
Input guess
20
Too low
Input guess
100
Too high
Input guess
97
You got it ..
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