📝 What You’ll Learn

• How the while loop works
• How the do...while loop works
• Differences between the two
• Common patterns and pitfalls
• Real-world examples

🔄 What is a While Loop?

A while loop keeps running as long as its condition is true.

🔧 Syntax:

while (condition) {
    // code to repeat
}

✅ Example

int i = 1;

while (i <= 5) {
    System.out.println("i = " + i);
    i++;
}

🔁 This prints i = 1 through i = 5.

🔂 The do...while Loop

This version always runs at least once — because the condition is checked after the first execution.

🔧 Syntax:

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

Example:

int i = 1;

do {
    System.out.println("i = " + i);
    i++;
} while (i <= 5);

🔍 When to Use Which?

Use this...	When...
while	You may want to skip the loop entirely
do...while	You always want it to run at least once

⚠️ Common Mistakes

• Forgetting to update the loop variable (infinite loop!)
• Misplacing semicolons:

  while (i < 5); // ❌ Don't do this
  

• Using assignment instead of comparison:

  while (x = 5) // ❌ should be while (x == 5)
  

🛠 Real-Life Example

Password Retry Simulation:

Scanner scanner = new Scanner(System.in);
String password;

do {
    System.out.print("Enter password: ");
    password = scanner.nextLine();
} while (!password.equals("java123"));

System.out.println("Access granted!");

📘 Recap

• while loops check condition before running
• do...while loops run at least once
• Be careful with infinite loops and condition logic