Digits Sort

Create a C# console application that extracts all digits from a text string and displays them in sorted order.

Solution

This app demonstrates string parsing, character validation, and sorting. It accepts any text input containing a mix of letters, numbers, and special characters, extracts only the numeric digits, sorts them in ascending order, and displays the result as a continuous sequence.

namespace DigitsSort
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Input text with digits: ");
            var str = Console.ReadLine();

            // Counting digits in the text string
            var count = 0;
            foreach (var c in str!)
            {
                if (char.IsDigit(c))
                {
                    count++;
                }
            }

            // Creating an array to store digits
            var m = new int[count];
            var index = 0;
            foreach (var c in str)
            {
                if (char.IsDigit(c))
                {
                    m[index] = Convert.ToInt32(c.ToString());
                    index++;
                }
            }

            // Sorting the array using selection sort
            for (int i = 0; i < count; i++)
            {
                for (int j = i + 1; j < count; j++)
                {
                    if (m[i] > m[j])
                    {
                        int temp = m[i];
                        m[i] = m[j];
                        m[j] = temp;
                    }
                }
            }

            // Displaying the sorted result
            Console.Write("Sorted result: ");
            foreach (int item in m)
            {
                Console.Write(item);
            }
        }
    }
}

Features

• Accepts mixed alphanumeric input text
• Extracts only digit characters (0-9)
• Ignores letters, spaces, and special characters
• Sorts extracted digits using Selection Sort algorithm
• Displays sorted digits as a continuous string
• Two-pass algorithm: counting then extraction

Requirements

• .NET Framework or .NET Core/5+
• C# compiler

Usage

1. Run the application
2. Enter any text containing digits (letters and symbols are allowed)
3. The program will extract all digits and display them sorted in ascending order

Example Usage

Input text with digits: Hello123World456
Sorted result: 123456

Input text with digits: abc9def3ghi7jkl1
Sorted result: 1379

Input text with digits: Order #4582 - Price: $19.99
Sorted result: 124589999

Input text with digits: No numbers here!
Sorted result:

How It Works

Step 1: Count Digits

var count = 0;
foreach (var c in str!)
{
    if (char.IsDigit(c))
    {
        count++;
    }
}

First pass through the string counts how many digit characters exist.

Step 2: Extract Digits

var m = new int[count];
var index = 0;
foreach (var c in str)
{
    if (char.IsDigit(c))
    {
        m[index] = Convert.ToInt32(c.ToString());
        index++;
    }
}

Second pass extracts digits and stores them as integers in an array.

Step 3: Sort Digits (Selection Sort)

for (int i = 0; i < count; i++)
{
    for (int j = i + 1; j < count; j++)
    {
        if (m[i] > m[j])
        {
            int temp = m[i];
            m[i] = m[j];
            m[j] = temp;
        }
    }
}

Sorts the digit array in ascending order using Selection Sort.

Step 4: Display Results

foreach (int item in m)
{
    Console.Write(item);
}

Outputs sorted digits as a continuous string without spaces.

Algorithm Analysis

Time Complexity

• Counting pass: O(n) where n is input string length
• Extraction pass: O(n)
• Sorting: O(d²) where d is number of digits
• Overall: O(n + d²)

Space Complexity

• Array storage: O(d) for digit array
• Overall: O(d)

Since d ≤ n and typically d << n, the algorithm is quite efficient.

Building and Running

Using Visual Studio

1. Open the project in Visual Studio
2. Press F5 or click "Start" to build and run

Using .NET CLI

dotnet run

Technical Details

Character Validation

• Uses char.IsDigit(c) to identify numeric characters
• Works with Unicode digit characters (0-9)
• Filters out all non-digit characters automatically

Digit Conversion

• Converts char to string: c.ToString()
• Converts string to integer: Convert.ToInt32()
• Alternative: int.Parse() or c - '0' for ASCII arithmetic

Null-Forgiving Operator

• str! tells compiler that ReadLine() won't return null
• Safe in this context since we're iterating immediately

Educational Value

This project is excellent for learning:

• String manipulation: Parsing and character-level processing
• Character classification: Using char.IsDigit() and similar methods
• Two-pass algorithms: Counting before allocation
• Type conversion: Converting between char, string, and int
• Array manipulation: Dynamic sizing based on input
• Sorting algorithms: Applying Selection Sort to extracted data
• Filtering data: Separating relevant from irrelevant information

Use Cases

Practical applications of this algorithm:

• Data cleaning: Extracting numeric codes from mixed text
• Phone number extraction: Getting digits from formatted numbers
• ID validation: Sorting identification numbers
• Log parsing: Extracting numeric values from log files
• Form processing: Validating and organizing numeric input

Possible Enhancements

Consider these extensions:

• Sort in descending order option
• Remove duplicate digits
• Count frequency of each digit
• Extract and sort multi-digit numbers (not just single digits)
• Support for negative numbers
• Display original vs sorted side-by-side
• Add option to use Array.Sort() for comparison
• Extract digits while preserving their groupings

Edge Cases

The program handles:

• No digits: Creates empty array, displays nothing
• Only digits: Processes entire input
• Unicode characters: Properly identifies digit characters
• Empty input: Handles gracefully (creates size-0 array)

Alternative Sorting

For production code, consider using built-in sorting:

Array.Sort(m);

The manual Selection Sort implementation is provided for educational purposes.

Source Code

Please refer to the GitHub repository.