Every useful program behaves differently depending on something.

If the user is logged in, show the dashboard. If not, show the login screen. If a score is above 90, print an A. If it is below 60, print an F.

That is control flow.

The fork in the road

Think of your program as a traveler on a road. At certain points, the road splits. The traveler checks a sign (the condition) and takes one path or the other.

            condition?
                |
        --------+--------
        |                |
      true              false
        |                |
   run this block    skip it

Every decision in Dart starts with a condition.

You already know how to write conditions. They are the comparison and logical expressions from Lesson 5: age >= 18, score < 60, name == 'Ali'.

if

The simplest decision: run a block of code only when a condition is true.

void main() {
  var age = 20;
  if (age >= 18) {
    print('You can vote.');
  }
}

The condition goes inside (...). The code to run goes inside {...}.

If the condition is true, the block runs. But if it is false, Dart skips it entirely. Nothing happens.

if / else

What if you want to do something when the condition is false?

void main() {
  var age = 16;
  if (age >= 18) {
    print('You can vote.');
  } else {
    print('You cannot vote yet.'); // this runs, age is 16
  }
}

else handles the false path. One branch always runs. But never both.

if / else if / else

What if there are more than two paths?

void main() {
  var score = 85;
  if (score >= 90) {
    print('A');
  } else if (score >= 80) {
    print('B'); // this runs, 85 >= 80
  } else if (score >= 70) {
    print('C');
  } else {
    print('F');
  }
}

Dart checks conditions from top to bottom. It runs the first one that is true, then stops. If none are true, else runs.

You can add as many else if branches as you need. The final else is optional.

Ternary

When an if / else assigns a single value, you can write it on one line:

void main() {
  var age = 20;
  var label = age >= 18 ? 'Adult' : 'Minor';
  print(label); // Adult
}

Read it left to right: if the condition is true, use the first value. If it is false, use the second.

The ternary is for simple one-value choices. But if you need to do more than assign a single value, use a full if / else.

switch

When one variable can be one of several specific values, switch is cleaner than a long chain of else if:

void main() {
  var day = 'Monday';
 
  switch (day) {
    case 'Monday':
      print('Start of the week.'); // this runs
      break;
    case 'Friday':
      print('End of the work week.');
      break;
    default:
      print('Another day.');
  }
}

Each case matches one specific value. When a match is found, that block runs. break exits the switch. Without break, Dart gives a compile-time error.

default is the fallback. It runs when no case matches. It is optional, but a good habit.

Dart 3 added more powerful switch expressions and pattern matching. Those live in the Dart in Depth course.

Summary