While and Do While in Dart

While and do-while loops in Dart, including:

• 🔄 Concept & Syntax

• ✅ Solved examples

• ❓ Practice problems (unsolved)

• 📌 Differences

• 🧾 Summary

---

🔁 while and do-while Loops in Dart – Explained with Examples

---

💡 Introduction

Loops are used when we want to repeat something again and again. In Dart, apart from for, we also have while and do-while loops.

But what's the difference?

• 🧠 Use while when you don’t know how many times the loop should run.

• ✅ Use do-while when you want the loop to run at least once, even if the condition is false.

---

🧱 1. while Loop

🔁 Syntax:

while (condition) {
  // code to execute
}

🔍 How it works:

• Checks the condition first.

• If true, it runs the block.

• Keeps repeating as long as the condition is true.

---

✅ Example 1: Print numbers from 1 to 5

void main() {
  int i = 1;
  while (i <= 5) {
    print(i);
    i++;
  }
}

Output:

1
2
3
4
5

---

✅ Example 2: Find the sum of numbers from 1 to 10

void main() {
  int sum = 0, i = 1;
  while (i <= 10) {
    sum += i;
    i++;
  }
  print('Sum = $sum');
}

---

🧱 2. do-while Loop

🔁 Syntax:

do {
  // code to execute
} while (condition);

🔍 How it works:

• Executes the block first, then checks the condition.

• Even if the condition is false, the loop runs once.

---

✅ Example 1: Print “Hello” once even if condition is false

void main() {
  int i = 10;
  do {
    print('Hello');
  } while (i < 5);
}

Output:

Hello

---

✅ Example 2: Ask for password until correct (simulation)

import 'dart:io';
void main() {
  String password = '';
  do {
    stdout.write('Enter password: ');
    password = stdin.readLineSync()!;
  } while (password != 'admin123');
  print('Access Granted!');
}

---

🧠 break and continue in while and do-while

🔴 Using break to exit early

void main() {
  int i = 1;
  while (i <= 10) {
    if (i == 6) break;
    print(i);
    i++;
  }
}

---

🟡 Using continue to skip iteration

void main() {
  int i = 0;
  while (i < 5) {
    i++;
    if (i == 3) continue;
    print(i);
  }
}

---

❓ Unsolved Practice Problems

1. Print all even numbers from 1 to 100 using a while loop.

2. Count the number of digits in a number (e.g., 12345 → 5 digits).

3. Find the factorial of a number using do-while.

4. Keep asking the user for input until they enter a number greater than 50.

5. Reverse a number using a while loop (e.g., 123 → 321).

6. Use a do-while loop to simulate a simple login system.

---

🔍 Differences Between while and do-while

Feature	while Loop	do-while Loop
Condition check	Before loop body	After loop body
Guaranteed execution	❌ May not run at all	✅ Runs at least once
Use case	When unsure of execution	When one run is needed

---

🧾 Summary

• while loop: Checks condition first.

• do-while loop: Runs code first, checks later.

• Use break to exit, continue to skip.

• Great for repeating input, validations, and menus.

---

Contact us for software training, education or development