a_variables

Exercise A: Variables

Make a new project named variables using cargo
- See "cargo help" if you forgot the command.
Open Cargo.toml
- Change the version number to 2.3.4 and save the file. Keep an eye out for that version number in cargo's output when you run it!
In src/main.rs at the start of the main() function:
- Declare the variable missiles and initialize it to 8
- Declare the variable ready and initialize it to 2
Change the println!(...) at the end of main() to:
- println!("Firing {} of my {} missiles...", ready, missiles);
Run your program using cargo (see "cargo help" if you forgot the command). Some common errors you may hit:
- Forgot to use let to bind a variable
- Forgot a semicolon ; at the end of a line

After the println!(...), subtract ready from missiles like this:
- missiles = missiles - ready;
Add a second println!(...) to the end:
- println!("{} missiles left", missiles);
Run your program again using cargo
- Did you run into an error about mutability? Go back and add mut at the right spot on the line where you declare missiles.
Declare a constant named STARTING_MISSILES and set it to 8 (the type is i32).
Declare a constant named READY_AMOUNT and set it to 2 (also i32).
Use the constants to initialize missiles and ready
- Where did you put the constants? If you put them inside the main() function, try moving them up above main() to module scope!
Nice. Congratulate yourself on a job well done! You are a Rust programmer now!

Explicitly annotate the variables with the type i32
Try binding the variables all at once on one line using a pattern (parentheses and commas) -- can you figure out where mut goes?
- Can you figure out the correct type annotation when you assign them all in one line? Hint: it will use the same sort of pattern as the variables and values.
Instead of changing missiles, use the value missiles - ready directly in the second println!(...)
- What warning does cargo emit when you run your program now? Can you fix it?
Add another variable to your program but don't use it.
- What does cargo say when you run your program?
Try modifying a constant in main() (for example, READY_AMOUNT = 1). What does the error look like?