if/else

Branching with if-else is similar to other languages. Unlike many of them,
the boolean condition doesn’t need to be surrounded by parentheses, and each
condition is followed by a block. if-else conditionals are expressions,
and, all branches must return the same type.

  1. fn main() {
  2.     let n = 5;
  4.     if n < 0 {
  5.         print!("{} is negative", n);
  6.     } else if n > 0 {
  7.         print!("{} is positive", n);
  8.     } else {
  9.         print!("{} is zero", n);
  10.     }
  12.     let big_n =
  13.         if n < 10 && n > -10 {
  14.             println!(", and is a small number, increase ten-fold");
  16.             // This expression returns an `i32`.
  17.             10 * n
  18.         } else {
  19.             println!(", and is a big number, half the number");
  21.             // This expression must return an `i32` as well.
  22.             n / 2
  23.             // TODO ^ Try suppressing this expression with a semicolon.
  24.         };
  25.     //   ^ Don't forget to put a semicolon here! All `let` bindings need it.
  27.     println!("{} -> {}", n, big_n);
  28. }