Cannot resolve symbol

Question

I have a UnitTest and should test this method. I am getting the sum of strings. What I did is that I converted the string into integers and added them and store in the variable length as an Integer, and then I return the length. The problem that I have is that it is showing that it cannot resolve symbol length. I am using Rider as IDE and I changed the settings of the IDE, but it is still showing "Cannot resolve symbol length". I hope someone can help me to fix this.

internal string SumStrings(string value1, string value2)
{            
    int.Parse(length) = int.Parse(value1) + int.Parse(value2);
    return length;            
}

The UnitTest:

#region Sum of strings as string

// Create a method that returns the sum of two numbers.
    [Fact]
    public void ReturnsSumAsStringFromTwoString()
    {
        Assert.Equal("11", util.SumStrings("6","5"));
    }

    // Previous method must pass the following Multiple tests.
    [Theory]
    [InlineData("1", "1", "0")]
    [InlineData("1", "0", "1")]
    [InlineData("-1", "0", "-1")]
    [InlineData("1000", "500", "500")]
    public void TheoriesReturnsSumAsStringFromTwoString(string length, string value1, string value2)
    {
        Assert.Equal(length, util.SumStrings(value1, value2));
    }

    

Answer 1

This is not how you declare and assign a variable:

int.Parse(length) = int.Parse(value1) + int.Parse(value2);

This is:

var length = int.Parse(value1) + int.Parse(value2);

Or if you want to specify the type explicitly:

int length = int.Parse(value1) + int.Parse(value2);

Additionally, your method claims to have a return type of string but you are trying to return an int . Change the return type:

internal int SumStrings(string value1, string value2) {

As an aside, in your method you don't really need a separate variable at all, you can just return the calculated result directly:

internal int SumStrings(string value1, string value2) {
    return int.Parse(value1) + int.Parse(value2);
}

Answer 2

you are trying to do int.Parse(length) while the length is not defined yet, and you are not returning a string but an Int.

internal string SumStrings(string value1, string value2)
{            
    var length = int.Parse(value1) + int.Parse(value2);
    return length.ToString();            
}

would work, but be careful, what would happen if the input is not a number? better use TryParse

int number;

bool success = int.TryParse(value, out number);

a better solution would be something like this:

    internal string SumStrings(string value1, string value2)
    {
         if (int.TryParse(value1, out var num1) && int.TryParse(value2, out var num2))
         {
             return (num1+num2).ToString();
         }


         
         // throw new WrongInputException("wrong input");   
         // or some other default behavior as your requirements ask for
         // basically some kind of handling for bad input value
  }

as the comments section implies, you should of course catch the specific exception, and even create a new exception that suits your needs