# Exercise Chapter 3 in The Book of Rust

Exercise 1: Convert temperatures between Fahrenheit and Celsius.

```
fn f_to_c(degree: i32) -> i32{
((degree as f64 - 32.) * 5. / 9.).round() as i32
}
fn c_to_f(degree: i32) -> i32{
(degree as f64 / 5. * 9. + 32.).round() as i32
}
```

Exercise 2: Generate the nth Fibonacci number.

```
fn fibonacci(n: u32) -> u32{
if n == 0 { return 0 };
if n == 1 { return 1 };
fibonacci(n-2) + fibonacci(n-1)
}
```

Exercise 3:Print the lyrics to the Christmas carol “The Twelve Days of Christmas,” taking advantage of the repetition in the song.

```
fn the_12_of_days_of_xmas(){
let days = [
"first", "second", "third", "fourth",
"fifth", "sixth", "seventh", "eighth",
"ninth", "tenth", "eleventh", "twelfth"];
let presents = [
"a partridge in a pear tree", "two turtle doves","three French hens",
"four calling birds","five golden rings","six geese a-laying",
"seven swans a-swimming","eight maids a-milking","nine ladies dancing",
"ten lords a-leaping","eleven pipers piping","twelve drummers drumming"];
for index in 0..12 {
println!("{}.",index+1);
println!("On the {} day of Christmas my true love sent to me", days[index]);
for j in 0..index+1 {
if j == index{
println!("{}.",presents[index-j])
}else{
println!("{},",presents[index-j])
}
}
}
}
```

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