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Error in percentage calculation

Trying to calculate percentage amount but it always return a 0.
foreach (DataGridViewRow row in dataGridView1.Rows)
{
double igst_amt;
double amt = (Convert.ToDouble(row.Cells[dataGridView1.Columns[4].Index].Value)) * (Convert.ToDouble(row.Cells[dataGridView1.Columns[5].Index].Value));
row.Cells[dataGridView1.Columns[6].Index].Value = Convert.ToString(amt);
igst_amt = (igst/100)*(amt);
MessageBox.Show(Convert.ToString(igst_amt));
if (state == "o")
{
row.Cells[dataGridView1.Columns[9].Index].Value =Convert.ToString( (cgst / 100) *( amt));
row.Cells[dataGridView1.Columns[11].Index].Value =Convert.ToString( (sgst / 100) * (amt));
}
else if (state == "i")
{
row.Cells[dataGridView1.Columns[7].Index].Value = igst_amt;
}
double g_total = igst_amt + amt;
row.Cells[dataGridView1.Columns[13].Index].Value = Convert.ToString(g_total);
double t_g_total=0;
t_g_total+= g_total;
}

Let's break this down to the basic code required to reproduce the issue:
int igst = 10;
double amt = 42;
double igst_amt = (igst / 100) * (amt);
Console.WriteLine(igst_amt);
With this I get a result of 0.
However, if I write it like this:
double igst = 10;
double amt = 42;
double igst_amt = (igst / 100) * (amt);
Console.WriteLine(igst_amt);
Then I get 4.2.
I suspect that igst is actually an integer and you're performing integer arithmetic which will result in 0.
You should change igst to double or you can do this:
int igst = 10;
double amt = 42;
double igst_amt = igst * amt / 100;
Console.WriteLine(igst_amt);
A simple change to the calculation and it works.
Also, as a side note, you appear to be doing monetary calculations using double, but you should be using decimal as it is designed for money calculations.

Correct way for get fractional part double like int

I need get fractional part of double like int and only two numbers. My code
(int)Math.Floor(val * 100 - (int)val * 100)
but this can (int)val * 100 may be out of range of int or long. Ok.
If i try
(int)Math.Floor((val - (int)val) * 100)
Return value may be incorrect. For example:
double val = 56.9;
int retVal = (int)Math.Floor((val - (int)val) * 100);
// retVal = 89, because (val - (int)val) return 0.899999999675
How correct get fractional part of double like int?

Try this extensions method:
public static int GetFrac2Digits(this double d)
{
var str = d.ToString("0.00", CultureInfo.InvariantCulture);
return int.Parse(str.Substring(str.IndexOf('.') + 1));
}

try this
double val = 56.9;
double result=0;
int retVal = (int)Math.Floor((val - (int)val) * 100);
// retVal = 89, because (val - (int)val) return 0.899999999675
int FrctPart=result.ToString().Split('.')[1]

Like this maybe?
decimal d = (decimal)val;
int retVal = Math.Floor((d - Math.Floor(d)) * 100);
// 59.9 --> 90
// 123.456 --> 45

You could also use Math.Truncate instead of casting to int:
double val = 56.9;
int retVal = (int)Math.Round((val-Math.Truncate(val)) * 100);
// retVal is now 90

Dealing with imprecise, jittery gps signal

My goal is to use GPS to measure the distance that I moved with my phone. My problem is, that the results are imprecise. I've used the following code to calculate the distance:
public double getDistance(GeoCoordinate p1, GeoCoordinate p2)
{
double d = p1.Latitude * 0.017453292519943295;
double num3 = p1.Longitude * 0.017453292519943295;
double num4 = p2.Latitude * 0.017453292519943295;
double num5 = p2.Longitude * 0.017453292519943295;
double num6 = num5 - num3;
double num7 = num4 - d;
double num8 = Math.Pow(Math.Sin(num7 / 2.0), 2.0) + ((Math.Cos(d) * Math.Cos(num4)) * Math.Pow(Math.Sin(num6 / 2.0), 2.0));
double num9 = 2.0 * Math.Atan2(Math.Sqrt(num8), Math.Sqrt(1.0 - num8));
return (6376500.0 * num9);
}
This is my OnLocationChanged implementation:
bool begin = true;
public void OnLocationChanged(Location location)
{
_aktuellerOrt = location;
//aktuellerOrt.Speed is always 0, so I cannot use that.
if (_aktuellerOrt == null)
{
//message
}
else
{
if (_aktuellerOrt.Accuracy > 70) //I found values around 130 to be more or less good
{
_locationText.Text = String.Format("{0}, {1}", _aktuellerOrt.Latitude, _aktuellerOrt.Longitude);
GeoJetzt = new GeoCoordinate();
GeoJetzt.Latitude = _aktuellerOrt.Latitude;
GeoJetzt.Longitude = _aktuellerOrt.Longitude;
if (beginn)
{
GeoVorher = new GeoCoordinate();
GeoVorher.Latitude = _aktuellerOrt.Latitude;
GeoVorher.Longitude = _aktuellerOrt.Longitude;
beginn = false;
}
else
{
double abstand = getDistance(GeoVorher, GeoJetzt);
weg += abstand;
if (weg >= 1)
_distanzText.Text = weg + " kilometers";
else
_distanzText.Text = (weg * 1000) + " meters";
_distanzText.Text += " (" + abstand + ", " + _aktuellerOrt.Accuracy + ")";
GeoVorher = new GeoCoordinate();
GeoVorher.Latitude = _aktuellerOrt.Latitude;
GeoVorher.Longitude = _aktuellerOrt.Longitude;
}
}
else
_locationText.Text = "Too coarse, now " + _aktuellerOrt.Accuracy + ".";
}
}
The problem is, I get values for abstand within the kilometer range while not moving the phone.
What are best practices for imprecise signals? My goal is to measure the distance while jogging or running, so 10 - 16 km/h.

Getting runtime error, C# Converting Array to Int

for some reason this will compile but it comes out with an error at the end and I can't figure out why. The first part of the code is to display a table from a text file which works correctly, the second part doesn't.
I don't think it even gets to the Console.WriteLine bit, which was a way of checking whether it did. Can anyone see why?
Thanks for any help you can give!
class Program
{
static void Main(string[] args)
{
List<float> inputList = new List<float>();
TextReader tr = new StreamReader("c:/users/tom/documents/visual studio 2010/Projects/DistanceCalculator3/DistanceCalculator3/TextFile1.txt");
String input = Convert.ToString(tr.ReadToEnd());
String[] items = input.Split(',');
Console.WriteLine("Point Latitude Longtitude Elevation");
for (int i = 0; i < items.Length; i++)
{
if (i % 3 == 0)
{
Console.Write((i / 3) + "\t\t");
}
Console.Write(items[i]);
Console.Write("\t\t");
if (((i - 2) % 3) == 0)
{
Console.WriteLine();
}
}
Console.WriteLine();
Console.WriteLine();
// Ask for two bits of data which are then stored in Longtitude, Latitude and Elevation
Console.WriteLine("Please enter the two points that you wish to know the distance between:");
string point = Console.ReadLine();
string[] pointInput = point.Split(' ');
int pointNumber = Convert.ToInt16 (pointInput[0]);
int pointNumber2 = Convert.ToInt16 (pointInput[1]);
int Latitude = (Convert.ToInt16(items[pointNumber*3]));
int Longtitude = (Convert.ToInt16(items[(pointNumber*3)+1]));
int Elevation = (Convert.ToInt16(items[(pointNumber*3)+2]));
int Latitude2 = (Convert.ToInt16(items[pointNumber2 * 3]));
int Longtitude2 = (Convert.ToInt16(items[(pointNumber2 * 3) + 1]));
int Elevation2 = (Convert.ToInt16(items[(pointNumber2 * 3) + 2]));
Console.WriteLine("Latitude");
Console.WriteLine("Latitude2");

You are using decimal values, which cannot be converted into Int16. So use float.
Also, Outputting "Latitude" will write the variable's name, not its value.
I modified your code:
float Latitude = (float.Parse(items[pointNumber*3]));
float Longtitude = (float.Parse(items[(pointNumber*3)+1]));
float Elevation = (float.Parse(items[(pointNumber*3)+2]));
float Latitude2 = (float.Parse(items[pointNumber2 * 3]));
float Longtitude2 = (float.Parse(items[(pointNumber2 * 3) + 1]));
float Elevation2 = (float.Parse(items[(pointNumber2 * 3) + 2]));
Console.WriteLine(Latitude);
Console.WriteLine(Latitude2);

Your input strings are of floating values, not integers. You can parse to floats like this:
float Latitude = (Convert.ToSingle(items[pointNumber * 3]));
float Longtitude = (Convert.ToSingle(items[(pointNumber * 3) + 1]));
float Elevation = (Convert.ToSingle(items[(pointNumber * 3) + 2]));
float Latitude2 = (Convert.ToSingle(items[pointNumber2 * 3]));
float Longtitude2 = (Convert.ToSingle(items[(pointNumber2 * 3) + 1]));
float Elevation2 = (Convert.ToSingle(items[(pointNumber2 * 3) + 2]));

Generate a random number in a Gaussian Range?

I want to use a random number generator that creates random numbers in a gaussian range where I can define the median by myself. I already asked a similar question here and now I'm using this code:
class RandomGaussian
{
private static Random random = new Random();
private static bool haveNextNextGaussian;
private static double nextNextGaussian;
public static double gaussianInRange(double from, double mean, double to)
{
if (!(from < mean && mean < to))
throw new ArgumentOutOfRangeException();
int p = Convert.ToInt32(random.NextDouble() * 100);
double retval;
if (p < (mean * Math.Abs(from - to)))
{
double interval1 = (NextGaussian() * (mean - from));
retval = from + (float)(interval1);
}
else
{
double interval2 = (NextGaussian() * (to - mean));
retval = mean + (float)(interval2);
}
while (retval < from || retval > to)
{
if (retval < from)
retval = (from - retval) + from;
if (retval > to)
retval = to - (retval - to);
}
return retval;
}
private static double NextGaussian()
{
if (haveNextNextGaussian)
{
haveNextNextGaussian = false;
return nextNextGaussian;
}
else
{
double v1, v2, s;
do
{
v1 = 2 * random.NextDouble() - 1;
v2 = 2 * random.NextDouble() - 1;
s = v1 * v1 + v2 * v2;
} while (s >= 1 || s == 0);
double multiplier = Math.Sqrt(-2 * Math.Log(s) / s);
nextNextGaussian = v2 * multiplier;
haveNextNextGaussian = true;
return v1 * multiplier;
}
}
}
Then to verify the results I plotted them with gaussianInRange(0, 0.5, 1) for n=100000000
As one can see the median is really at 0.5 but there isn't really a curve visible. So what I'm doing wrong?
EDIT
What i want is something like this where I can set the highest probability by myself by passing a value.

The simplest way to draw normal deviates conditional on them being in a particular range is with rejection sampling:
do {
retval = NextGaussian() * stdev + mean;
} while (retval < from || to < retval);
The same sort of thing is used when you draw coordinates (v1, v2) in a circle in your unconditional normal generator.
Simply folding in values outside the range doesn't produce the same distribution.
Also, if you have a good implementation of the error function and its inverse, you can calculate the values directly using an inverse CDF. The CDF of a normal distribution is
F(retval) = (1 + erf((retval-mean) / (stdev*sqrt(2)))) / 2
The CDF of a censored distribution is
C(retval) = (F(retval) - F(from)) / (F(to) - F(from)), from ≤ x < to
To draw a random number using a CDF, you draw v from a uniform distribution on [0, 1] and solve C(retval) = v. This gives
double v = random.NextDouble();
double t1 = erf((from - mean) / (stdev*sqrt(2)));
t2 = erf((to - mean) / (stdev*sqrt(2)));
double retval = mean + stdev * sqrt(2) * erf_inv(t1*(1-v) + t2*v);
You can precalculate t1 and t2 for specific parameters. The advantage of this approach is that there is no rejection sampling, so you only need a single NextDouble() per draw. If the [from, to] interval is small this will be faster.
However, it sounds like you might want the binomial distribution instead.

I have similar methods in my Graph generator (had to modify it a bit):
Returns a random floating-point number using a generator function with a specific range:
private double NextFunctional(Func<double, double> func, double from, double to, double height, out double x)
{
double halfWidth = (to - from) / 2;
double distance = halfWidth + from;
x = this.rand.NextDouble() * 2 - 1;// -1 .. 1
double y = func(x);
x = halfWidth * x + distance;
y *= height;
return y;
}
Gaussian function:
private double Gauss(double x)
{
// Graph should look better with double-x scale.
x *= 2;
double σ = 1 / Math.Sqrt(2 * Math.PI);
double variance = Math.Pow(σ, 2);
double exp = -0.5 * Math.Pow(x, 2) / variance;
double y = 1 / Math.Sqrt(2 * Math.PI * variance) * Math.Pow(Math.E, exp);
return y;
}
A method that generates a graph using the random numbers:
private void PlotGraph(Graphics g, Pen p, double from, double to, double height)
{
for (int i = 0; i < 1000; i++)
{
double x;
double y = this.NextFunctional(this.Gauss, from, to, height, out x);
this.DrawPoint(g, p, x, y);
}
}
I would rather used a cosine function - it is much faster and pretty close to the gaussian function for your needs:
double x;
double y = this.NextFunctional(a => Math.Cos(a * Math.PI), from, to, height, out x);
The out double x parameter in the NextFunctional() method is there so you can easily test it on your graphs (I use an iterator in my method).