Convert array element as concatenated string to double in C#

Question

I'm (very) new to C#; I'm sure the solution here is simple but I can't figure it out.

Suppose I have a simple array of temperatures for Friday. I receive an abbreviation for the day and an hour (integer) from somewhere and I want to use it to print an element from the array:

using System;

public class Program
{
    public static void Main()
    {
        double[] Friday = {54.5, 61.0, 63.5, 58.0};
        string Today = "Fri";
        int Hour = 1;
        double parsed = Convert.ToDouble(Today + "day[" + int + "]");
        Console.WriteLine(parsed);
    }
}

Given these conditions, how do I output 61.0? Then end result should be equivalent to Console.WriteLine(Friday[1]);

What is the expected output? please be specific. Why did you put day[1] between qoutes? — Manar Husrieh
– Manar Husrieh, Commented Jan 25, 2015 at 8:57
Hi..please be specific about the question? Why do you want to convert the string as Today to a double? — Anurag
– Anurag, Commented Jan 25, 2015 at 9:24
Sorry about the misunderstanding. I rewrote my question as well as some of the code. The main thing is: formatting my concatenated string in such a way that it can return the array element. — Lloyd_Xmas
– Lloyd_Xmas, Commented Jan 25, 2015 at 9:57
I think what you are trying to accomplish is using Convert.ToDouble() in the same way as Javascripts Eval(). There is no equivalent for Eval in the c# language, nothing will simply take a string and interpret it as code. If you tell us some more information about what your ultimate goal is, we can find an alternative approach to the problem. — HugoRune
– HugoRune, Commented Jan 25, 2015 at 12:04

Patrice Gahide · Accepted Answer · 2015-01-25 12:07:42Z

1

If I really wanted to achieve that I would use a dictionary:

Dictionary<string, double[]> dayToValues =
  new Dictionary<string, double[]>
  {
    {"Monday", new double[] {1.0, 2.0, 3.0} },
    {"Friday", new double[] {4.0, 5.0, 6.0} }
  };

string today = "Fri";
int hour = 0;
double firstHourValue = dayToValues[today + "day"][hour];
Console.WriteLine(firstHourValue); // prints "4"

If you really need to dynamically build the name of a variable and access it, you have to use reflection. Something like:

string fieldName = today.ToLower() + "day";
double[] todays = GetType().GetField(fieldName, BindingFlags.NonPublic | BindingFlags.Instance).GetValue(this) as double[];
Console.WriteLine(todays[1]);  // prints "8"

This assumes that your have a private field in the current class:

double[] friday = { 7.0, 8.0, 9.0 };

Of course the reflection code depends on the exact location and scope of the variables. And obvioulsy you would need some null reference checks to use it in the real world. Anyway, using reflection looks quite irrelevant for what seem to be your needs. Use it only if you really have to.

edited Jan 25, 2015 at 12:07

answered Jan 25, 2015 at 10:01

Patrice Gahide

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1 Comment

Lloyd_Xmas Over a year ago

All responses I've seen so far have been helpful, however I think the dictionary approach is best given the particulars of the objective. Thank you much Patrice!

Richard Schneider · Accepted Answer · 2015-01-25 09:01:51Z

1

c# uses zero-relative indexing. This means that the 1st element in the array has an index of zero. So you most likely mean Friday[0].

c# also has the ToString method on all objects. This returns a "human readable" representation of the object. So you can do

 Console.WriteLine(Friday[0].ToString());

Also, WriteLine will auto-magically convert any object passed to it into its string repsentation. So this will also work

 Console.WriteLine(Friday[0]);

If you want text and a value, then use a Format string, as in

 Console.WriteLine("Friday {0}", Friday[0]);

See https://msdn.microsoft.com/en-us/library/system.string.format%28v=vs.110%29.aspx for more details on format strings.

edited Jan 25, 2015 at 9:01

answered Jan 25, 2015 at 8:55

Richard Schneider

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3 Comments

Farhad Jabiyev Over a year ago

IMO you have misunderstood the OP's question. He wants that Console.WriteLine("Fri" + "day[1]") statement to print 61.0.

Farhad Jabiyev Over a year ago

I have taken my downvote. But the answer is not solving the OP's problem neither. In your answer you have not used today variable. He wants to convert string to C# code. Console.WriteLine(today+"day[1]") =>Console.WriteLine(Friday[1])

Lloyd_Xmas Over a year ago

I rewrote my question to be more clear . . . Farhad, you are correct, I want it to output as if I was passing Friday[1] directly.

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