10.1 if/else

The if statement allows conditional branching of code.

The expression used as the condition needs to evaluate to a boolean value. If not, the compiler issues an error:

if 1 {
  println!("Hi");
}

[E0308] Error: mismatched types
   ╭─[ command_2:1:1 ]
   │
 1 │ if 1 {
   │    ┬  
   │    ╰── expected `bool`, found integer
───╯

Here is a correct conditional expression:

if 1 != 2 {
  println!("True");
}

True

Example of chained if/else:

let n = 5;
if n > 10 {
  println!("Yes");
} else if n < -20 {
  println!("Maybe");
} else {
  println!("No");
}

No

10.1.1As an expression¶

if/else statement can be used as an expression:

let n = 11;
let x = if n < 10 { 5.5 } else { -4.1 };
x

We can chain the if/else statements:

let s = "b";
let t = if s == "a" { (1,2) } else if s == "b" { (3,4) } else { (5,6) };
t