While Loop in Dart

Syntax

A while loop repeats as long as its condition remains true. The condition is checked before each iteration.

while (condition) {
  // runs while condition is true
}

Example

void main() {
  // Count 1 to 5
  int i = 1;
  while (i <= 5) {
    print('i = $i');
    i++;
  }

  // Sum until total exceeds 50
  int total = 0;
  int num = 1;
  while (total <= 50) {
    total += num;
    num++;
  }
  print('Total: $total after adding $num numbers');

  // Simulate user input validation
  int attempts = 0;
  String password = 'dart123';
  String input = 'wrong';
  while (input != password && attempts < 3) {
    attempts++;
    print('Attempt $attempts: wrong password');
    if (attempts < 3) input = 'wrong'; else input = 'dart123';
  }
  print('Access granted: $${input == password}');
}

i = 1 ... i = 5
Total: 56 after adding 11 numbers
Attempt 1: wrong password
Attempt 2: wrong password
Attempt 3: wrong password
Access granted: true

When to Use While

Use while when you do not know the number of iterations in advance — for example, reading input until the user types "quit", or processing data until a condition changes.

⚠️ Infinite Loop Warning

Always ensure the condition eventually becomes false, or use break to exit. Forgetting to update the loop variable causes an infinite loop:

// DANGER — infinite loop:
int x = 0;
while (x < 5) {
  print(x);
  // x is never incremented!
}

🧠 Quiz

Summary

The while loop checks its condition before each iteration. Use it when the number of iterations is unknown. Always update the condition variable inside the loop to avoid infinite loops.