Reverse A Number In Dart

Reversing a number is a common task in programming that involves taking a given number and reversing its digits. This concept is important because it helps in understanding string manipulation, number processing, and algorithms. It is often used in interview questions and can be applied in various fields, including data validation and numerical analysis.

What is Reversing a Number?

Reversing a number means transforming a number, such as 1234, into its reverse, 4321. This process can help programmers practice working with integers and strings, and it serves as a good exercise in algorithmic thinking. Understanding how to reverse a number can also aid in developing more complex algorithms in areas like data structures, cryptography, and more.

Syntax

// Function to reverse a number
int reverseNumber(int num) {
  // Initialize a variable to hold the reversed number
  int reversed = 0;

  // Loop until the number becomes 0
  while (num != 0) {
    // Get the last digit of the number
    int digit = num % 10;
    
    // Update the reversed number
    reversed = reversed * 10 + digit;
    
    // Remove the last digit from the original number
    num ~/= 10; // Using integer division
  }

  // Return the reversed number
  return reversed;
}

How It Works

1. We define a function reverseNumber that takes an integer as input.
2. We initialize a variable reversed to store the reversed number.
3. We use a while loop to iterate as long as the number is not zero.
4. Inside the loop, we extract the last digit using the modulus operator %.
5. We update the reversed variable by multiplying it by 10 and adding the extracted digit.
6. We then remove the last digit from the original number using integer division ~/.
7. Finally, we return the reversed number.

Example 1: Basic Usage

Example
Copy
void main() {
  int number = 1234; // The number to be reversed
  int reversedNumber = reverseNumber(number); // Call the function
  print(reversedNumber); // Print the reversed number
}
Try it Yourself

Output:

4321

Explanation: The input number 1234 is reversed to 4321 using the reverseNumber function.

Example 2: Reversing Negative Numbers

void main() {
  int number = -5678; // A negative number
  int reversedNumber = reverseNumber(-number); // Reverse the positive part
  print(-reversedNumber); // Print the reversed number with a negative sign
}

Output:

-8765

Explanation: The negative number -5678 is reversed to -8765 by reversing its positive part and then reapplying the negative sign.

Example 3: Real-World Application

void main() {
  int userInput = 890; // Simulating user input
  // Call the function to reverse the input
  int reversedNumber = reverseNumber(userInput);
  // Check if the reversed number is a palindrome
  if (userInput == reversedNumber) {
    print("$userInput is a palindrome.");
  } else {
    print("$userInput is not a palindrome.");
  }
}

Output:

890 is not a palindrome.

Explanation: This example demonstrates how reversing a number can be used to check if a number is a palindrome (reads the same forward and backward).

Example 4: Edge Cases

void main() {
  int number = 0; // Edge case: zero
  int reversedNumber = reverseNumber(number); // Reverse the number
  print(reversedNumber); // Print the reversed number
}

Output:

0

Explanation: The edge case of reversing zero results in zero, as it does not change.

Example 5: Advanced Usage - Reversing a Number with Input Validation

void main() {
  int number = 12345; // Example input
  if (number >= 0) { // Check for non-negative input
    int reversedNumber = reverseNumber(number);
    print(reversedNumber);
  } else {
    print("Please enter a non-negative integer."); // Error message for invalid input
  }
}

Output:

54321

Explanation: This example ensures that only non-negative integers are accepted for reversal, providing a user-friendly error message for invalid input.

When to Use Reverse a Number in Dart

Key Points