Dart While Loop
Repeating code based on conditions
🔄 What is While Loop?
While loops repeat code as long as a condition remains true. Unlike for loops, you don't need to know the exact number of iterations beforehand. Perfect for user input validation and conditional repetition.
// Simple while loop example
void main() {
int count = 1;
while (count <= 5) {
print('Count: $count');
count++; // Important: update the condition variable
}
}
While Loop Characteristics
Condition Check
Tests condition before each iteration
while (condition) {
// code here
}Variable Update
Must update condition variable inside loop
while (i < 10) {
print(i);
i++; // Update
}Infinite Loop Risk
Can run forever if condition never becomes false
// Dangerous!
while (true) {
print('Forever');
}Flexible Control
Great for unknown iteration counts
while (userInput != 'quit') {
// process input
}🔹 Basic While Loop
A simple counting example with while loop:
void main() {
int number = 1;
print('Counting from 1 to 5:');
while (number <= 5) {
print('Number: $number');
number++; // Increment to avoid infinite loop
}
print('Loop finished!');
}Output:
Counting from 1 to 5:
Number: 1
Number: 2
Number: 3
Number: 4
Number: 5
Loop finished!
🔹 While Loop with User Input
Keep asking for input until a specific condition is met:
import 'dart:io';
void main() {
String password = '';
String correctPassword = 'dart123';
while (password != correctPassword) {
print('Enter password:');
password = stdin.readLineSync() ?? '';
if (password != correctPassword) {
print('Wrong password! Try again.');
}
}
print('Access granted!');
}Sample Output:
Enter password:
Wrong password! Try again.
Enter password:
Access granted!
🔹 While Loop with Lists
Process list elements using while loop:
void main() {
List tasks = ['Study', 'Exercise', 'Cook', 'Read'];
int index = 0;
print('My daily tasks:');
while (index < tasks.length) {
print('${index + 1}. ${tasks[index]}');
index++;
}
} Output:
My daily tasks:
1. Study
2. Exercise
3. Cook
4. Read
🔹 While Loop with Break and Continue
Control loop execution with break and continue statements:
void main() {
int number = 0;
while (number < 10) {
number++;
if (number == 5) {
continue; // Skip printing 5
}
if (number == 8) {
break; // Exit loop when reaching 8
}
print('Number: $number');
}
print('Loop ended at: $number');
}Output:
Number: 1
Number: 2
Number: 3
Number: 4
Number: 6
Number: 7
Loop ended at: 8
🔹 Common While Loop Patterns
Useful patterns for different scenarios:
🔸 Sum Until Condition
void main() {
int sum = 0;
int number = 1;
while (sum < 50) {
sum += number;
print('Added $number, sum is now: $sum');
number++;
}
}🔸 Menu System
void main() {
String choice = '';
while (choice != 'quit') {
print('\nMenu: 1-Start, 2-Settings, quit-Exit');
// choice = getUserInput(); // Simulated
if (choice == '1') {
print('Starting application...');
} else if (choice == '2') {
print('Opening settings...');
}
}
}🔹 While vs For Loop
Choose the right loop for your situation:
Use While Loop When:
- Unknown iterations: Don't know how many times to repeat
- Condition-based: Continue until something happens
- User input: Keep asking until valid input
- File processing: Read until end of file
Use For Loop When:
- Known iterations: Exact number of repetitions
- Array/List processing: Go through all elements
- Counting: Simple increment/decrement patterns