Search code examples
c#mathwebrequest

Why isn't my math right

I'm trying to make a simple tool in which you can track your invest with BTC. I have all the data a need to calculate everything but when comes to the exchange price changing my "investment total" doesn't change. Meaning when BTC goes up, my result of how much money I made stays the same almost and the same for when it goes down.

I have posted my code and tried a bunch of different solutions, including different types: floats, decimals, int's, doubles and it always turns out the same way. What am I missing?

enter image description here

EDIT - CODE:

namespace BTC_Profit_Projections
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

        }
        Core c = new Core();

        private void button1_Click(object sender, EventArgs e)
        {
            timer1.Enabled = true;
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            var ExchangeRate = c.GrabBTCAmount();
            var AmountInBTC = (c.USDtoBTC(15000, ExchangeRate));
            var AmountAtMarket = (AmountInBTC * ExchangeRate);

            ListViewItem i = new ListViewItem("15000");
            i.SubItems.Add(AmountInBTC.ToString());
            i.SubItems.Add(AmountAtMarket.ToString());
            i.SubItems.Add(ExchangeRate.ToString());
            mainlist.Items.Add(i);
        }
    }
}

Core Class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading.Tasks;

namespace BTC_Profit_Projections
{
    class Core
    {

        public decimal GrabBTCAmount()
        {
            WebClient w = new WebClient();
            string btc = w.DownloadString("https://www.bitstamp.net/api/ticker/");

            int pos1 = btc.IndexOf("last", 0);
            int pos2 = btc.IndexOf(":", pos1);
            int pos3 = btc.IndexOf(",", pos2);

            return Convert.ToDecimal(btc.Substring(pos2 + 3, pos3 - pos2 - 4));

        }

        public decimal USDtoBTC(decimal money, decimal rate) 
        {
            return money / rate;
        }
    }
}
Solution

  • It is not clear why you expect this code to behave differently. Look at these lines:

            var ExchangeRate = c.GrabBTCAmount();
        var AmountInBTC = (c.USDtoBTC(15000, ExchangeRate));
        var AmountAtMarket = (AmountInBTC * ExchangeRate);

    If I inline USDtoBTC and inline everything to calculate AmountAtMarket the formula would be 

    AmountAtMarket  = (15000 / ExchangeRate) * ExchangeRate

    So you should always get 15000 with some rounding error.

    The bug seems to be in the line where you calculate AmountInBTC. To calculate AmountInBTC you should divide your investment sum (I assume 15000) by the exchange rate at the moment you did your investment rather than current exchange rate.