using System;

public class Program

{

    public struct frame {

        public int f;

        public double x;

        public double y;

        public frame(int f1, double x1, double y1) {

            f = f1;

            x = x1;

            y = y1;

        }

    }

    public struct keyFrame {

        public int frame;

        public bool valid;

        public double x;

        public double y;

        public keyFrame(int f, double x1, double y1) {

            frame = f;

            valid = true;

            x = x1;

            y = y1;

        }

    }

    public static void Main()

    {

        keyFrame x0 = new keyFrame (0,1,0);

        keyFrame x1 = new keyFrame (1,0,2);

        keyFrame x2 = new keyFrame ();

        keyFrame x3 = new keyFrame (3,10,0);

        keyFrame[] kf = new keyFrame[4];

        frame[] f = new frame[4];

        kf[0] = x0;

        kf[1] = x1;

        kf[2] = x2;

        kf[3] = x3;

​

        for(int i = 0; i < kf.Length; i++) {

            if(kf[i].valid == false) {

                //f[i].x = (kf[i-1].x +  kf[i+1].x)/2;

                for (int k = i+1; k < kf.Length; k++) {

                }

                f[i].f = i;

            } else {

                f[i].x = kf[i].x;

                f[i].y = kf[i].y;

                f[i].f = kf[i].frame;

            }

        }

        for(int i = 0; i < kf.Length; i++) {

            Console.WriteLine(f[i].x);

        }

    }

}