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copied!<pre><code>using System; public static class DecimalExtensions { public static int DigitAtPosition(this decimal number, int position) { if (position <= 0) { throw new ArgumentException("Position must be positive."); } if (number < 0) { number = Math.Abs(number); } number -= Math.Floor(number); if (number == 0) { return 0; } if (position == 1) { return (int)(number * 10); } return (number * 10).DigitAtPosition(position - 1); } } </code></pre> <p><strong>Edit</strong>: If you wish, you may separate the recursive call from the initial call, to remove the initial conditional checks during recursion:</p> <pre><code>using System; public static class DecimalExtensions { public static int DigitAtPosition(this decimal number, int position) { if (position <= 0) { throw new ArgumentException("Position must be positive."); } if (number < 0) { number = Math.Abs(number); } return number.digitAtPosition(position); } static int digitAtPosition(this decimal sanitizedNumber, int validPosition) { sanitizedNumber -= Math.Floor(sanitizedNumber); if (sanitizedNumber == 0) { return 0; } if (validPosition == 1) { return (int)(sanitizedNumber * 10); } return (sanitizedNumber * 10).digitAtPosition(validPosition - 1); } </code></pre> <hr> <p>Here's a few tests:</p> <pre><code>using System; using Xunit; public class DecimalExtensionsTests { // digit positions // 1234567890123456789012345678 const decimal number = .3216879846541681986310378765m; [Fact] public void Throws_ArgumentException_if_position_is_zero() { Assert.Throws<ArgumentException>(() => number.DigitAtPosition(0)); } [Fact] public void Throws_ArgumentException_if_position_is_negative() { Assert.Throws<ArgumentException>(() => number.DigitAtPosition(-5)); } [Fact] public void Works_for_1st_digit() { Assert.Equal(3, number.DigitAtPosition(1)); } [Fact] public void Works_for_28th_digit() { Assert.Equal(5, number.DigitAtPosition(28)); } [Fact] public void Works_for_negative_decimals() { const decimal negativeNumber = -number; Assert.Equal(5, negativeNumber.DigitAtPosition(28)); } [Fact] public void Returns_zero_for_whole_numbers() { const decimal wholeNumber = decimal.MaxValue; Assert.Equal(0, wholeNumber.DigitAtPosition(1)); } [Fact] public void Returns_zero_if_position_is_greater_than_the_number_of_decimal_digits() { Assert.Equal(0, number.DigitAtPosition(29)); } [Fact] public void Does_not_throw_if_number_is_max_decimal_value() { Assert.DoesNotThrow(() => decimal.MaxValue.DigitAtPosition(1)); } [Fact] public void Does_not_throw_if_number_is_min_decimal_value() { Assert.DoesNotThrow(() => decimal.MinValue.DigitAtPosition(1)); } [Fact] public void Does_not_throw_if_position_is_max_integer_value() { Assert.DoesNotThrow(() => number.DigitAtPosition(int.MaxValue)); } } </code></pre>

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