Reverse a Number in Dart

In Dart programming, as in many other programming languages, manipulating numbers is a fundamental skill.

Among these manipulations, the ability to reverse a number is particularly intriguing and useful.

This technique isn’t just about understanding numbers; it’s about mastering the art of manipulating data structures and algorithms in Dart, which is the backbone of Flutter apps.

In this guide, we’ll delve into the nuances of reversing numbers, a skill that can be applied in various scenarios such as solving algorithmic problems, developing unique app features, or simply enhancing your problem-solving toolkit in Dart.

Section 1: Fundamental Concepts

Understanding Number Types in Dart

In Dart, numbers mainly come in two types: int and double.

  • int: This is used for whole numbers. In Dart, an int is any non-decimal number without a fractional component. Examples are 123, -456, 7890.
  • double: This type represents floating-point numbers, which include decimals. Examples include 12.34, -56.78, 9.0.

Understanding these types is crucial because the method of reversing a number might slightly vary based on whether you’re dealing with an int or a double.

The Concept of Number Reversal

Reversing a number essentially means to invert the sequence of its digits. For example, reversing 1234 would give us 4321. This process might seem straightforward but requires a good understanding of data type conversion and manipulation in Dart.

Why is this important? Number reversal finds its application in various programming scenarios, such as:

  • Algorithmic challenges and puzzles, where such manipulations are a common requirement.
  • In certain algorithms, like palindrome checking where reversing a number can be a crucial step.
  • Unique features in applications, like generating certain types of numeric codes or identifiers.

Section 2: Reversing a Number in Dart

String Conversion Method

One of the most straightforward methods to reverse a number in Dart is by using string conversion. This method involves converting the number into a string, reversing the string, and then converting it back to a number. Let’s break down the steps:

  1. Convert the Number to a String: Dart allows easy conversion of numbers to strings using the toString() method.
  2. Reverse the String: Once the number is converted to a string, you can reverse it using the split(), reversed, and join() methods.
  3. Convert the String Back to a Number: Finally, convert the reversed string back to a number using int.parse() for integers or double.parse() for floating-point numbers.

Here’s an example to illustrate this method:

int reverseNumber(int number) {
    // Step 1: Convert the number to a string
    String numStr = number.toString();

    // Step 2: Reverse the string
    String reversedStr = numStr.split('').reversed.join('');

    // Step 3: Convert the string back to a number
    int reversedNum = int.parse(reversedStr);

    return reversedNum;

void main() {
    int originalNumber = 12345;
    int reversedNumber = reverseNumber(originalNumber);
    print("Original: $originalNumber, Reversed: $reversedNumber");

In this example, reverseNumber function takes an integer number, converts it to a string, reverses that string, and then parses the reversed string back to an integer. The main function demonstrates how to use this reverseNumber function.

Mathematical Approach

The mathematical approach to reversing a number involves using modulus and division operations. This method is particularly suited for integers and involves the following steps:

  1. Initialize a Variable for the Reversed Number: Start with a variable set to 0 that will hold the reversed number.
  2. Loop through the Original Number: Extract each digit using the modulus operator and build the reversed number by multiplying the current reversed number by 10 and adding the extracted digit.
  3. Return the Reversed Number: Once the original number is reduced to 0, return the reversed number.

Here’s a Dart function demonstrating this approach:

int reverseNumberMathematically(int number) {
    int reversedNumber = 0;
    while (number != 0) {
        int digit = number % 10; // Extracting the last digit
        reversedNumber = reversedNumber * 10 + digit; // Building the reversed number
        number = number ~/ 10; // Removing the last digit
    return reversedNumber;

void main() {
    int originalNumber = 12345;
    int reversedNumber = reverseNumberMathematically(originalNumber);
    print("Original: $originalNumber, Reversed: $reversedNumber");

Section 3: Handling Edge Cases

Dealing with Negative Numbers

To effectively reverse negative numbers, you can:

  • Detect if the number is negative.
  • If negative, convert it to positive, reverse it, and then reapply the negative sign.

Example Code:

int reverseNumberHandlingNegative(int number) {
    bool isNegative = number < 0;
    number = isNegative ? -number : number;
    int reversedNumber = reverseNumberMathematically(number);
    return isNegative ? -reversedNumber : reversedNumber;


Reversing a number in Dart can be achieved through different methods, each with its use cases and efficiencies. Understanding these techniques enhances your capability to solve various programming challenges and implement unique features in Flutter applications.

Hussain Humdani

Hussain Humdani

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