Dart Lesson 14 of 102 3 min read

if, else if and else in Dart

Learn conditional statements in Dart: if, else if, else, nested conditions and if-case, with clear examples and common mistakes.

An if statement runs a block of code only when a condition is true.

if #

void main() {
  var temperature = 31;

  if (temperature > 30) {
    print('It is hot today.');
  }
}

It is hot today.

if and else #

else runs when the condition is false. Exactly one of the two blocks runs.

void main() {
  var marks = 38;

  if (marks >= 40) {
    print('Pass');
  } else {
    print('Fail');
  }
}

Fail

else if #

Chain as many checks as you need. Dart tests them from the top and runs the first one that is true, then skips the rest.

void main() {
  var marks = 76;

  if (marks >= 90) {
    print('Grade A+');
  } else if (marks >= 80) {
    print('Grade A');
  } else if (marks >= 60) {
    print('Grade B');
  } else {
    print('Grade C');
  }
}

Grade B

Order matters. If you tested marks >= 60 first, a score of 95 would be labelled Grade B.

Combining conditions #

void main() {
  var age = 25;
  var hasLicence = true;

  if (age >= 18 && hasLicence) {
    print('You may drive.');
  } else if (age >= 18) {
    print('You need a licence first.');
  } else {
    print('You are too young to drive.');
  }
}

You may drive.

Nested if, and how to avoid it #

You can put an if inside another, but deep nesting is hard to read. Often you can flatten it by handling the “no” cases first and returning early.

String checkLogin(String user, String password) {
  if (user.isEmpty) return 'Enter a user name';
  if (password.length < 8) return 'Password is too short';
  return 'Welcome, $user';
}

void main() {
  print(checkLogin('', 'secret123'));
  print(checkLogin('rina', '123'));
  print(checkLogin('rina', 'secret123'));
}

Enter a user name
Password is too short
Welcome, rina

if-case: test a shape and take values out #

Dart 3 lets an if match a pattern. The block runs only if the value has the shape you describe.

void main() {
  var point = [3, 4];

  if (point case [var x, var y]) {
    print('x is $x and y is $y');
  }
}

x is 3 and y is 4

Common mistakes #

• Using = instead of ==. = assigns, == compares. Dart reports an error because an assignment is not a bool.
• A stray semicolon. if (x > 5); ends the statement right there, so the block below it always runs.
• Skipping the braces. A single statement works without { }, but adding a second line later creates a bug. Use braces unless the whole if fits on one line.

Try it yourself #

Write a program with an hour variable from 0 to 23. Print “Good morning” before 12, “Good afternoon” before 17, “Good evening” before 21 and “Good night” otherwise.