using System;

using Xunit;

public class Program

{

    public static void Main()

    {

        StringCalculatorTests.RunAllTests();

    }

}

​

public class StringCalculator

{

    public int Add(string input)

    {

        var symbol = '+';

        var sequence = input;

        // This will check if there is a "//[symbol]\n" sequence at the start of the input,

        // which indicates that the default symbol of '+' is being replaced.

        if(input.Length > 3 && input.Substring(0, 2) == "//")

        {

            symbol = input[2];

            sequence = input.Substring(4);

        }

        // Now we will use Split() to remove the symbol and grab all the numbers.

        var numbers = sequence.Split(symbol);

        var sum = 0;

        foreach(string number in numbers)

        {

            // This converts each number from a type of string to integer.

            if(int.TryParse(number, out int result))

            {

                if(result < 0) throw new Exception("Negative numbers not allowed!");

                if(result > 999) continue;

                sum += result;

            }

        }   

        return sum;

    }

}

​

​

public static class StringCalculatorTests

{

    public static void RunAllTests()

    {

        Should_Pass_Step_One();

        Console.WriteLine("Test 1 Passed!");

        Should_Pass_Step_Two();

        Console.WriteLine("Test 2 Passed!");

​

        Should_Pass_Step_Three();

        Console.WriteLine("Test 3 Passed!");

        Should_Pass_Step_Four();

        Console.WriteLine("Test 4 Passed!");

        Should_Pass_Step_Five();

        Console.WriteLine("Test 5 Passed!");

        Should_Pass_Step_Six();

        Console.WriteLine("Test 6 Passed!");

        Should_Pass_Step_Seven();

        Console.WriteLine("Test 7 Passed!");

        Should_Pass_Step_Eight();

        Console.WriteLine("Test 8 Passed!");

    }

    public static void Should_Pass_Step_One()

    {

        // Arrange

        var target = new StringCalculator();

        // Act

        var result = target.Add("");

        // Assert

        Assert.Equal(0, result);

    }

    public static void Should_Pass_Step_Two()

    {

        // Arrange

        var target = new StringCalculator();

        // Act

        var result = target.Add("1");

        var result2 = target.Add("3");

        // Assert

        Assert.Equal(1, result);

        Assert.Equal(3, result2);

    }

    public static void Should_Pass_Step_Three()

    {

        // Arrange

        var target = new StringCalculator();

        // Act

        var result = target.Add("1+2");

        var result2 = target.Add("3+5");

        // Assert

        Assert.Equal(3, result);

        Assert.Equal(8, result2);

    }

    public static void Should_Pass_Step_Four()

    {

        // Arrange

        var target = new StringCalculator();

        // Act

        var result = target.Add("1+2+3");

        var result2 = target.Add("3+5+3+9");

        // Assert

        Assert.Equal(6, result);

        Assert.Equal(20, result2);

    }

    public static void Should_Pass_Step_Five()

    {

        // Arrange

        var target = new StringCalculator();

        // Act

        var result = target.Add("3+3\n+3");

        var result2 = target.Add("4+\n5\n+4+4");

        // Assert

        Assert.Equal(9, result);

        Assert.Equal(17, result2);

    }

    public static void Should_Pass_Step_Six()

    {

        // Arrange

        var target = new StringCalculator();

        // Act & Assert

        var ex = Assert.Throws<Exception>(() => target.Add("-1+2-3"));

        Assert.Equal("Negative numbers not allowed!", ex.Message);

    }

    public static void Should_Pass_Step_Seven()

    {

        // Arrange

        var target = new StringCalculator();

        // Act

        var result = target.Add("1000+1001+2");

        // Assert

        Assert.Equal(2, result);

    }

    public static void Should_Pass_Step_Eight()

    {

        // Arrange

        var target = new StringCalculator();

        // Act

        var result = target.Add("//,\n11,1,2");

        var result2 = target.Add("//@\n1@2@3");

        // Assert

        Assert.Equal(14, result);

        Assert.Equal(6, result2);

    }

}