C# Calculate Percentage

Simple percentage calculation as an injectable service.

Yeah I got tired of Google’ling which number number you divide by each time I needed to do this in code :)

Simply put this is: (100 * scoreAchieved) / outOf which is generally (100 * small number) / big number.

Interface

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namespace Foo.Common.Maths.Interfaces
{
    public interface IPercentageCalculator
    {
        /// <summary>
        /// Calculate the score achieved as a percentage out of the given value `outOf`
        /// </summary>
        /// <param name="scoreAchieved">Example: 73</param>
        /// <param name="outOf">Example: 100</param>
        /// <returns>73.00 as the default decimal spacing is .00 (2 digits)</returns>
        double GetPercentage(int scoreAchieved, int outOf);

        /// <summary>
        /// Calculate the score achieved as a percentage out of the given value `outOf`
        /// </summary>
        /// <param name="scoreAchieved">Example: 73</param>
        /// <param name="outOf">Example: 100</param>
        /// <param name="digits">Example: 3</param>
        /// <returns>73.000</returns>
        double GetPercentage(int scoreAchieved, int outOf, int digits);
    }
}

Implementation

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using System;

namespace Foo.Common.Maths
{
    ///<inheritdoc/>
    public class PercentageCalculator : IPercentageCalculator
    {
        private const int DIGITS = 2;

        public double GetPercentage(int scoreAchieved, int outOf)
        {
            if (scoreAchieved == 0 || outOf == 0)
                return 0;

            return GetPercentage(scoreAchieved, outOf, DIGITS);
        }

        public double GetPercentage(int scoreAchieved, int outOf, int digits)
        {
            if (scoreAchieved == 0 || outOf == 0)
                return 0;

            return Math.Round((double)(100 * scoreAchieved) / outOf, digits);
        }
    }
}

References