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Control Flow

22 April, 2020   ·   Rust

if, if else, else if

An if expression allows you to branch your code depending on conditions.

fn main() {
  let num: i8 = 2;

  if num < 5 {
    println!("Number is Samll");
  } else if num % 2 === 0 {
    println!("Divisible by 2");
  } else {
    println!("Number is Big");
  }
}

In Rust, condition must resolve to a value of type bool, i.e. either true or false. Otherwise the program won’t compile.

let in if Statement

fn main() {
  let isTrue = true;
  let aNumber = if isTrue {
    5   // no semicolon
  } else {
    10  // no semicolon
  }
}
// also, data type should be same for each if-else
// block

Since if is an expression, it can be assigned to variable. But it is also worth mentioning that the data type of all the if, else blocks. Otherwise the following error would occur:

error[E0308]: if and else have incompatible types

Loops

loop

fn main() {
  let mut counter = 0;
  let value = loop {
    counter += 1;

    if counter == 10 {
      break counter * 2; // here, semicolon needed
    }
  }

  println!("Value is {}", value);
}

loop is a keyword used for running an infinite loop. This loop could be ended using break keyword.

loop is capable of returning value. Any expression/value placed after break keyword would be returned.

while

while is a conditional loop built-in to Rust.

fn main() {
  let mut number = 3;

  while number != 0 {
      println!("{}!", number);

      number -= 1;
  }
}

Using while loop as a replacement of for loop would result in slow execution of code, as compiler would add runtime code for checking checking index out of bound error.

for

fn main() {
  let a = [1, 2, 4, 5, 6];

  for element in a.iter() {
    println!("{}", element);
  }
}

Given an array of items, a for loop would iterate over each of them and pass the value to defind variable. In above case, element.

fn main() {
  for number in (1..4).rev() {
      println!("{}!", number);
  }

  println!("LIFTOFF!!!");
}
  1. sources/temp-conversion.rs
 control-flow  if  if-else
Functions↠ ↞Ownership