Dart Do-While Loop

Mastering Dart Do-While Loops| Comprehensive Quiz and Explanations

Introduction:

Unlock your understanding of Dart’s do-while loops with our comprehensive quiz! Whether you’re a beginner or looking to solidify your knowledge, this quiz covers everything from syntax to best practices. Dive into 15 questions designed to challenge and reinforce your grasp of do-while loops in Dart, followed by detailed explanations to help you master this fundamental concept. Let’s test and enhance your Dart skills together!

In Dart, a do-while loop  executes a block of code repeatedly until a specified condition evaluates to false. The key difference between a do-while loop and a regular while loop is that in a do-while loop, the condition is checked after the loop body has been executed, meaning the loop body is guaranteed to execute at least once.

Here’s the syntax of a do-while loop in Dart:

dart

do {
// code block to be executed
} while (condition);

Here’s an example to demonstrate how a do-while loop works in Dart:

dart

void main() {
int count = 0;

do {
print('Count is: $count');
count++;
} while (count < 5);
}

In this example, the loop will execute the code block (printing the current count) and then check the condition count < 5. If the condition is true, the loop will continue; otherwise, it will terminate. Since the condition is checked after the first iteration, the loop will execute at least once, regardless of the condition.

let’s delve a bit deeper into the do-while loop in Dart and explore some additional aspects and use cases.

Incrementing Values:

A common use case for loops is to increment a value each iteration. You can use shorthand increment operators like ++ or +=:

dart

void main() {
int count = 0;

do {
print('Count is: $count');
count++; // Increment count by 1
} while (count < 5);
}

Dart Do while Loop with Input Validation:

Do-while loops are handy for input validation scenarios, ensuring that the provides valid input before proceeding:

dart

import 'dart:io';

void main() {
String Input;

do {
print('Enter your name:');
Input = stdin.readLineSync();
} while (Input.isEmpty);

print('Hello, $Input!');
}

Infinite Loops:

Be cautious when using do-while loops to avoid infinite loops. Ensure that the condition will eventually become false to prevent the program from running indefinitely:

dart

void main() {
int count = 0;

do {
print('Count is: $count');
count--; // This will cause an infinite loop!
} while (count > 0);
}

Exiting Early:

You can use break statement to exit the loop prematurely based on some condition:

dart

void main() {
int count = 0;

do {
print('Count is: $count');
if (count == 3) {
break; // Exit the loop when count reaches 3
}
count++;
} while (true); // Infinite loop
}

Do-While vs. While:

Lastly, remember that while the do-while loop guarantees the execution of the loop body at least once, the while loop checks the condition before the first iteration, which means the loop body may not execute if the condition is initially false.

dart

void main() {
int count = 5;

// While loop
while (count < 5) {
print('While loop: Count is: $count');
count++;
}

// Do-while loop
do {
print('Do-while loop: Count is: $count');
count++;
} while (count < 5);
}

Output:

Do-while loop: Count is: 5

In this example, the do-while loop executes once even though the condition is initially false, while the while loop doesn’t execute at all.

Examples with explanation about the uses of Dart Do-While Loop

Let’s go through a couple of complete examples with explanations showcasing the uses of the Dart do-while loop.

Example 1: Guessing Game

In this example, we’ll create a simple guessing game where the has to guess a randomly generated number.

dart

import 'dart:math';
import 'dart:io';

void main() {
// Generate a random number between 1 and 100
Random random = Random();
int randomNumber = random.nextInt(100) + 1;

int guess;
int attempts = 0;

print('Welcome to the Guessing Game!');

do {
// Prompt the for a guess
stdout.write('Enter your guess (1-100): ');
guess = int.parse(stdin.readLineSync()!);

// Check the guess
if (guess < randomNumber) {
print('Too low. Try again.');
} else if (guess > randomNumber) {
print('Too high. Try again.');
}

attempts++;
} while (guess != randomNumber);

print('Congratulations! You guessed the correct number $randomNumber in $attempts attempts.');
}

Explanation:

• We use the Random class from the dart:math library to generate a random number between 1 and 100.
• Inside the do-while loop, we prompt the to enter a guess.
• We compare the ‘s guess with the randomly generated number and provide feedback.
• The loop continues until the guesses the correct number.
• After the loop exits, we print a congratulatory message along with the number of attempts it took to guess the correct number.

Example 2: Password Validation

In this example, we’ll create a simple password validation program where the has to enter a password until it matches a predefined password.

dart

import 'dart:io';

void main() {
final String correctPassword = 'password123';
String Input;

print('Please enter the password to access the system:');

do {
stdout.write('Password: ');
Input = stdin.readLineSync()!;

if (Input != correctPassword) {
print('Incorrect password. Try again.');
}
} while (Input != correctPassword);

print('Access granted! Welcome to the system.');
}

Explanation:

• We define a correctPassword variable with a predefined password.
• Inside the do-while loop, we prompt the to enter a password.
• We compare the ‘s input with the correct password.
• If the passwords don’t match, we inform the and prompt for input again.
• The loop continues until the enters the correct password.

These examples illustrate how the do-while loop can be used for scenarios where you need to execute a block of code at least once, such as input validation or repeatedly prompting until a condition is met.

Example 3: Calculating Factorial

In this example, we’ll calculate the factorial of a given number using a do-while loop.

dart

import 'dart:io';

void main() {
int number;
int factorial = 1;

stdout.write('Enter a number to calculate its factorial: ');
number = int.parse(stdin.readLineSync()!);

if (number < 0) {
print('Factorial is not defined for negative numbers.');
return;
}

int i = 1;

do {
factorial *= i;
i++;
} while (i <= number);

print('The factorial of $number is: $factorial');
}

Explanation:

• We prompt the to enter a number for which they want to calculate the factorial.
• We check if the entered number is negative. Factorial is not defined for negative numbers.
• Inside the do-while loop, we initialize i to 1 and calculate the factorial iteratively until i reaches the entered number.
• We multiply factorial by i in each iteration and increment i.
• After the loop, we print the calculated factorial.

Example 4: Countdown Timer

In this example, we’ll create a simple countdown timer using a do-while loop.

dart

import 'dart:async';

void main() async {
int seconds = 10;

print('Starting countdown:');

do {
print('$seconds seconds remaining...');
await Future.delayed(Duration(seconds: 1)); // Delay for 1 second
seconds--;
} while (seconds > 0);

print('Time\'s up!');
}

Explanation:

• We initialize a variable seconds to 10 to represent the countdown duration.
• Inside the do-while loop, we print the remaining seconds and wait for 1 second using Future.delayed.
• We decrement seconds in each iteration.
• The loop continues until seconds becomes 0.
• After the loop, we print “Time’s up!” to indicate the end of the countdown.

Example 5: Reading Input Until Exit

In this example, we’ll create a simple program that continuously reads input until the decides to exit.

dart

import 'dart:io';

void main() {
String Input;

do {
stdout.write('Enter a message (type "exit" to quit): ');
Input = stdin.readLineSync()!;
print('You entered: $Input');
} while (Input.toLowerCase() != 'exit');

print('Goodbye!');
}

Explanation:

• Inside the do-while loop, we continuously prompt the to enter a message.
• We read the input using stdin.readLineSync().
• The loop continues until the types “exit” (case-insensitive).
• Once the types “exit”, the loop exits, and we print “Goodbye!”.

Example 6: Generating Fibonacci Series

In this example, we’ll generate the Fibonacci series up to a specified number of terms using a do-while loop.

dart

import 'dart:io';

void main() {
int terms;
int first = 0;
int second = 1;
int count = 2; // Already initialized with first two terms

stdout.write('Enter the number of terms for Fibonacci series: ');
terms = int.parse(stdin.readLineSync()!);

if (terms < 1) {
print('Invalid input. Please enter a positive integer.');
return;
}

print('Fibonacci series:');
print('$first\n$second'); // Printing first two terms

do {
int next = first + second;
print('$next');
first = second;
second = next;
count++;
} while (count < terms);
}

Explanation:

• We prompt the to enter the number of terms they want in the Fibonacci series.
• We initialize first and second with the first two terms of the series.
• Inside the do-while loop, we calculate the next term by adding first and second.
• We update the values of first and second for the next iteration.
• The loop continues until the desired number of terms is generated.

Example 7: Menu-Driven Program

In this example, we’ll create a simple menu-driven program where the can choose different options.

dart

import 'dart:io';

void main() {
int choice;

do {
print('Menu:');
print('1. Option 1');
print('2. Option 2');
print('3. Option 3');
print('4. Exit');

stdout.write('Enter your choice: ');
choice = int.parse(stdin.readLineSync()!);

switch (choice) {
case 1:
print('You selected Option 1');
break;
case 2:
print('You selected Option 2');
break;
case 3:
print('You selected Option 3');
break;
case 4:
print('Exiting program...');
break;
default:
print('Invalid choice. Please enter a number between 1 and 4.');
}
} while (choice != 4);
}

Explanation:

• Inside the do-while loop, we continuously display a menu with different options.
• We prompt the to enter their choice.
• Based on the ‘s choice, we use a switch statement to perform the corresponding action.
• If the chooses to exit (option 4), the loop exits, and the program terminates.
• Otherwise, the menu is displayed again, and the loop continues.

Example 8: Simulating a Dice Roll Game

In this example, we’ll simulate a simple dice roll game where the keeps rolling a six-sided die until they choose to stop.

dart

import 'dart:io';
import 'dart:math';

void main() {
final Random random = Random();
int diceValue;
String Input;

print('Welcome to the Dice Roll Game!');

do {
stdout.write('Press enter to roll the dice (or type "exit" to quit): ');
Input = stdin.readLineSync()!;

if (Input.toLowerCase() == 'exit') {
print('Exiting game...');
break;
}

diceValue = random.nextInt(6) + 1;
print('You rolled a $diceValue');
} while (true);
}

Explanation:

• Inside the do-while loop, we continuously prompt the to roll the dice or exit the game.
• We use a Random object to generate a random number representing the value of the dice roll.
• If the types “exit”, the loop exits, and the game ends.
• Otherwise, we display the value of the dice roll and continue rolling until the decides to exit.

Anapplication about Dart Do-While Loop with explanation

Let’s create a simple application in Dart that utilizes a do-while loop.

Application: Multiplication Table Generator

This application will generate a multiplication table for a given number entered by the .

dart

import 'dart:io';

void main() {
print('Multiplication Table Generator');
print('-------------------------------');

int number;

// Prompt the to enter a number
stdout.write('Enter a number to generate its multiplication table: ');
number = int.parse(stdin.readLineSync()!);

print('\nMultiplication Table for $number:');
print('----------------------------------');

int multiplier = 1;

// Generate and print the multiplication table using a do-while loop
do {
int result = number * multiplier;
print('$number x $multiplier = $result');
multiplier++;
} while (multiplier <= 10); // Generate table up to 10

print('----------------------------------');
print('End of Multiplication Table');
}

Explanation:

• The application starts by prompting the to enter a number for which they want to generate the multiplication table.
• It then enters a do-while loop where the multiplication table is generated.
• Inside the loop, it multiplies the entered number by the current multiplier (initially 1) to get the result.
• The result is printed in the format “number x multiplier = result”.
• The multiplier is incremented in each iteration.
• The loop continues until the multiplier reaches 10, generating the multiplication table up to 10.
• After the loop, a message indicating the end of the multiplication table is printed.

Sample Output:

Multiplication Table Generator
——————————-
Enter a number to generate its multiplication table: 7

Multiplication Table for 7:
———————————-
7 x 1 = 7
7 x 2 = 14
7 x 3 = 21
7 x 4 = 28
7 x 5 = 35
7 x 6 = 42
7 x 7 = 49
7 x 8 = 56
7 x 9 = 63
7 x 10 = 70
———————————-
End of Multiplication Table
This application demonstrates how a do-while loop can be used to generate a repetitive task, such as printing a multiplication table, until a specified condition is met.

Quiz about Dart Do-While Loop:15 questions with explanations

Below is a quiz about Dart do-while loops. Each question is followed by multiple-choice options, and after each question, there’s an explanation of the correct answer.

Quiz: Dart Do-While Loop

1-What is the purpose of a do-while loop?

A. To execute a block of code repeatedly while a condition is true.
B. To execute a block of code at least once and then repeat it based on a condition.
C. To execute a block of code only if a condition is true.
D. To execute a block of code a fixed number of times.
Correct Answer: B. To execute a block of code at least once and then repeat it based on a condition.

Explanation: Unlike the while loop, the do-while loop guarantees the execution of the block of code at least once, regardless of the condition.

2-Which keyword is used to exit a do-while loop prematurely?

A. return
B. continue
C. exit
D. break
Correct Answer: D. break

Explanation: The break statement is used to exit a loop prematurely based on a certain condition.

3-What will happen if the condition of a do-while loop is initially false?

A. The loop will never execute.
B. The loop will execute indefinitely.
C. The loop will execute once and then terminate.
D. The loop will prompt the to enter a condition.
Correct Answer: C. The loop will execute once and then terminate.

Explanation: Unlike a while loop, which checks the condition before the first iteration, a do-while loop executes the block of code once before checking the condition.

4-Which of the following is a valid do-while loop in Dart?

dart

A. do { } while ();
B. do { } while;
C. do while ();
D. while { } do;

Correct Answer: A. do { } while ();

Explanation: In Dart, the correct syntax for a do-while loop is do { } while (condition);.

5-In a do-while loop, when is the condition evaluated?

A. Before each iteration.
B. After each iteration.
C. Only before the first iteration.
D. Only after the last iteration.
Correct Answer: B. After each iteration.

Explanation: The condition of a do-while loop is evaluated after each iteration, which means the loop will execute at least once regardless of the condition.

6-Which of the following is the correct way to increment a variable inside a do-while loop?

A. count = count + 1;
B. count++;
C. count += 1;
D. All of the above.
Correct Answer: D. All of the above.

Explanation: All the options provided are valid ways to increment a variable in Dart, but count++ is the most concise and commonly used method.

7-What happens if the condition of a do-while loop is always true?

A. The loop executes indefinitely.
B. The loop terminates immediately.
C. The loop executes once and then terminates.
D. The loop will not execute.
Correct Answer: A. The loop executes indefinitely.

Explanation: If the condition of a do-while loop is always true, the loop will execute indefinitely unless terminated using a break statement or other control flow mechanism.

8-Which of the following statements about do-while loops is true?

A. A do-while loop must always have a condition.
B. A do-while loop may not execute at all if the condition is false initially.
C. A do-while loop guarantees the execution of the block of code at least once.
D. A do-while loop cannot contain a break statement.
Correct Answer: C. A do-while loop guarantees the execution of the block of code at least once.

Explanation: Unlike a while loop, which may not execute if the condition is false initially, a do-while loop guarantees the execution of the block of code at least once.

9-Which keyword is used to define the end of a do-while loop block in Dart?

A. endwhile
B. end
C. done
D. while
Correct Answer: none

Explanation: In Dart, there is no specific keyword used to mark the end of a do-while loop block. The end of the loop block is determined by the closing curly brace }.

10-When should you use a do-while loop instead of a while loop?

A. When you want to execute a block of code repeatedly while a condition is true.
B. When you want to execute a block of code only if a condition is true.
C. When you want to execute a block of code at least once and then repeat it based on a condition.
D. When you want to execute a block of code a fixed number of times.
Correct Answer: C. When you want to execute a block of code at least once and then repeat it based on a condition.

Explanation: Use a do-while loop when you want to ensure that the block of code executes at least once before the condition is evaluated.

11-Which of the following is the syntax of a do-while loop in Dart?

A. do { } while ();
B. while () { } do;
C. do while ();
D. do { } while;
Correct Answer: A. do { } while ();

Explanation: In Dart, the correct syntax for a do-while loop is do { } while (condition);.

12-Which operator is used to concatenate strings in Dart?

A. +
B. &
C. %
D. |
Correct Answer: A. +

Explanation: In Dart, the + operator is used to concatenate strings.

13-In Dart, how do you prompt the to enter input from the command line?

A. input()
B. getInput()
C. readLineSync()
D. getInput()
Correct Answer: C. readLineSync()

Explanation: In Dart, the stdin.readLineSync() function is used to read input from the command line.

14-Which of the following is used to represent a block of code in Dart?

A. ()
B. {}
C. []
D. <>
Correct Answer: B. {}

Explanation: In Dart, a block of code is represented by curly braces { }.

15-What happens if a do-while loop’s condition is always false?

A. The loop executes indefinitely.
B. The loop terminates immediately.
C. The loop executes once and then terminates.
D. The loop will not execute.
Correct Answer: C. The loop executes once and then terminates.

Explanation: If the condition of a do-while loop is false initially, the loop will execute once and then terminate, as the condition is checked after each iteration.