Control flow (if, for, while, switch) in Flutter

Introduction

Control flow helps your app decide what to do next. It lets your app choose between options, repeat tasks, or pick actions based on conditions.

Show a message only if a user is logged in.

Repeat a list of items to display them on the screen.

Keep asking for input until the user provides a valid answer.

Choose different screens to show based on user choices.

Syntax

Flutter

if (condition) {
  // code to run if condition is true
} else if (anotherCondition) {
  // code if anotherCondition is true
} else {
  // code if none above are true
}

for (var item in collection) {
  // code to run for each item
}

while (condition) {
  // code to repeat while condition is true
}

switch (variable) {
  case value1:
    // code for value1
    break;
  case value2:
    // code for value2
    break;
  default:
    // code if no case matches
    break;
}

if checks conditions and runs code accordingly.

for repeats code for each item in a list.

while repeats code while a condition stays true.

switch picks code to run based on a variable's value.

Examples

Checks if age is 18 or more, then prints 'Adult', otherwise 'Child'.

Flutter

if (age >= 18) {
  print('Adult');
} else {
  print('Child');
}

Prints 'Number 0', 'Number 1', and 'Number 2' one by one.

Flutter

for (var i = 0; i < 3; i++) {
  print('Number $i');
}

Repeats printing count until it reaches 3.

Flutter

int count = 0;
while (count < 3) {
  print('Count is $count');
  count++;
}

Prints 'Stop' because color is 'red'.

Flutter

var color = 'red';
switch (color) {
  case 'red':
    print('Stop');
    break;
  case 'green':
    print('Go');
    break;
  default:
    print('Wait');
    break;
}

Sample App

This app shows a greeting based on the current time. It uses if and else if to pick the right greeting.

Flutter

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    int hour = DateTime.now().hour;
    String greeting;

    if (hour < 12) {
      greeting = 'Good morning!';
    } else if (hour < 18) {
      greeting = 'Good afternoon!';
    } else {
      greeting = 'Good evening!';
    }

    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('Control Flow Example')),
        body: Center(
          child: Text(
            greeting,
            style: const TextStyle(fontSize: 24),
          ),
        ),
      ),
    );
  }
}

Important Notes

Always make sure your while loops have a way to stop, or your app may freeze.

Use break; in switch cases to stop checking further cases.

Indent your code inside control flow blocks to keep it clear and easy to read.

Summary

Control flow lets your app make decisions and repeat tasks.

if, for, while, and switch are common ways to control flow.

Use them to create interactive and dynamic apps.