Do-While Loops but the values for the while statement is inside the Do Statement

Question

I am trying to learn C# by making a program that finds two values in which the system becomes equilibrium. I tried the Do-While loop but I can't establish the while statement since the values for the while statement is inside the Do-statement. It just says "The variables does not exist in the current context". I hope I make sense.

Update: The complete code is posted below. I tried the while (true) statement and added a if-break statement. I don't really know if this is how the if-break statement works. The loop goes on and on without end. I tried printing the values but from the very first loop, it already satisfies the conditions.

Below is my code:

using System;
using System.Linq;

public class BoltCoord
{
    public double x1;
    public double y1;
}

public class Program
{
    public static void Main()
    {
        Console.Write("Number of Rows: ");
        int nrow = int.Parse(Console.ReadLine());

        Console.Write("Spacing of Rows: ");
        double srow = double.Parse(Console.ReadLine());

        Console.Write("Number of Columns: ");
        int ncol = int.Parse(Console.ReadLine());

        Console.Write("Spacing of Columns: ");
        double scol = double.Parse(Console.ReadLine());

        Console.Write("Eccentricity from CG: ");
        double ecc = double.Parse(Console.ReadLine());

        Console.Write("Rotation: ");
        double rot = double.Parse(Console.ReadLine());

        int totalbolts = nrow * ncol;

        var boltgroupCG = BoltCG(nrow, ncol, srow, scol); // bolt group cg from first bolt

        double[] xvaluesofbolts = new double[totalbolts]; //x-values of each bolt where first bolt is (0,0)
        for (int ctr = 0; ctr < totalbolts; ctr++)
        {
            xvaluesofbolts[ctr] = (ctr % ncol) * srow;
        }

        double[] yvaluesofbolts = new double[totalbolts]; //y-values of each bolt where first bolt is (0,0)
        for (int ctr = 1; ctr < totalbolts; ctr++)
        {
            yvaluesofbolts[ctr] = (ctr / ncol) * srow;
        }

        double[] FxOfBolts = new double[totalbolts];
        double[] FyOfBolts = new double[totalbolts];
        double[] MomOfBolts = new double[totalbolts];
        double[] XTransOfBolts = new double[totalbolts]; // Translated X
        double[] YTransOfBolts = new double[totalbolts]; // Translated Y

        double[] XLi = new double[totalbolts]; // Translated X
        double[] YLi = new double[totalbolts]; // Translated Y

        double[] BoltDist = new double[totalbolts]; // from IC
        double[] DeformBolts = new double[totalbolts];
        double[] ReactionForce = new double[totalbolts];
        double[] ReactionForceX = new double[totalbolts];
        double[] ReactionForceY = new double[totalbolts];
        double[] MomentBolt = new double[totalbolts];

        var IC = new BoltCoord(); // from CG

        double Px;
        double Py;
        double sumRx;
        double sumRy;
        double ctrX;
        double ctrY;

        do
        {
            for (ctrX = 0; ctrX < 50; ctrX = ctrX + 0.1)
            {
                for (ctrY = 0; ctrY < 50; ctrY = ctrY + 0.1)
                {
                    for (int El = 0; El < totalbolts; El++)
                    {
                        XTransOfBolts[El] = xvaluesofbolts[El] - boltgroupCG.x1;
                        YTransOfBolts[El] = yvaluesofbolts[El] - boltgroupCG.y1;
                        XLi[El] = XTransOfBolts[El] + ctrX;
                        YLi[El] = YTransOfBolts[El] + ctrY;
                        BoltDist[El] = Math.Sqrt(Math.Pow(XLi[El], 2) + Math.Pow(YLi[El], 2));

                        double MaxDist = BoltDist.Max();
                        // int MaxIndex = Array.IndexOf(BoltDist, MaxDist);
                        double delta = 0.34;
                        double Rult = 74;


                        DeformBolts[El] = delta * BoltDist[El] / MaxDist;
                        ReactionForce[El] = Rult * Math.Pow((1 - Math.Exp(-10 * DeformBolts[El])), 0.55);

                        ReactionForceX[El] = ReactionForce[El] * YLi[El] / BoltDist[El];
                        ReactionForceY[El] = ReactionForce[El] * XLi[El] / BoltDist[El];

                        MomentBolt[El] = ReactionForce[El] * BoltDist[El];

                        sumRx = ReactionForceX.Sum();
                        sumRy = ReactionForceY.Sum();
                        double sumMoment = MomentBolt.Sum();
                        double sumReax = ReactionForce.Sum();

                        double ro = (ecc + ctrX) * Math.Cos(Math.PI * rot / 180) + ctrY * Math.Sin(Math.PI * rot / 180);
                        Px = sumMoment / ro;
                        Py = Px * Math.Cos(Math.PI * rot / 180);

                        Console.WriteLine(Px + " " + sumRx + " " + Py + " " + sumRy); // tried printing the values to see if loop happens. 
                                                                                      // Px minus sumRx and Py minus sumRy are always less than 1000 but
                                                                                      // loop still continues?

                        if ((Px - sumRx <= 1000) && (Py - sumRy <= 1000))
                        {
                            break;
                        }

                    }
                }
            }
        } while (true); //((Px != sumRx) || (Py != sumRy));
    }

    public static BoltCoord BoltCG(int nrow, int ncol, double srow, double scol)
    {
         var BoltCGCoord = new BoltCoord
         {
             x1 = (ncol - 1) * scol * 0.5,
             y1 = (nrow - 1) * srow * 0.5
         };
         return BoltCGCoord;
    }
}

Answer 1

If you replace

while ((Px != sumRx) || (Py != sumRy))

with

while (true)

does the code compile?

If not, then make sure you declared the variables Px, Py, sumRx, sumRy before the start of the do-while loop.

double Px, Py, sumRx, sumRy;
do
{
...

Answer 2

I put your code into dotnetfiddle.net, and the error I get when changing the while statement to

while((Px != sumRx) || (Py != sumRy))

is Use of unassigned local variable 'Px' . To not get this error you need to assign a value to Px sumRx Py and sumRy before starting the loop. Above the loop you can just change your initialization to

double Px = 0;
double Py = 0;
double sumRx = 0;
double sumRy = 0;
double ctrX = 0;
double ctrY = 0;

Also, your break statement isn't working because the break statement applies to your current loop block which is your innermost for loop, so you are breaking out of the innermost for loop, and not breaking out of the while loop.

Answer 3

The general answer to why the loop goes on and on is that your for loop is going to check every condition, which means that it will loop nrow * ncol number of times even if it does find the answer on the first time through. This is assuming that in the code you're running this line isn't commented out. (while true will totally loop forever and ever).

    } while (true); //((Px != sumRx) || (Py != sumRy));

The break statement in there bails out of the inner most for loop. If you want to keep breaking out early you'll need to also write break out logic for all the loops. In general that's pretty ugly though and it is a great example of why nesting loops and if statements can get ugly very fast. :)

Hope that helps.