Terrain Modification Script index out of range?

I am making a script to make my terrain blocky like in minecraft but since I am new to unity3d's terrain class it is proving a challenge, I do not know why but I get a IndexOutOfRangeError on line 23. Also if you see any other problems please tell me! Thanks!

Code:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public static class TerrainToBlocks {
 
     public static int xRes;
     public static int yRes;
 
     public static void GetTerrainValues(TerrainData td,GameObject terrainObject){
         Debug.Log ("Started");
         xRes = td.heightmapWidth;
         yRes = td.heightmapHeight;
         float[,] heights = td.GetHeights (0, 0, td.heightmapWidth, td.heightmapHeight);
         RoundNumbers (xRes,yRes,heights,terrainObject);
         Debug.Log ("Step 1 Complete.");
     }
     
     private static void RoundNumbers(int x, int y,float[,] old,GameObject terrainObject){
         float[,] newHeights = new float[xRes,yRes];
         for(int i = 0; i < x; i++){
             for(int k = 0; i < y; k++){
                 newHeights[i,k] = Mathf.RoundToInt(old[i,k]);
             }
         }
         GenerateBlocks (newHeights,x,y,terrainObject);
         Debug.Log ("Step 2 Complete.");
     }
 
     private static void GenerateBlocks(float[,] hMap,int x, int y,GameObject terrainObject){
         for(int i = 0; i < x; i++){
             for(int k = 0; i < y; k++){
                 float xVal = (float)i;
                 float yVal = (float)hMap[i,k];
                 float zVal = (float)k;
                 Vector3 pos = new Vector3(xVal,yVal,zVal);
                 GameObject newCube = GameObject.CreatePrimitive(PrimitiveType.Cube);
                 newCube.transform.position = pos;
             }
         }
         Object.DestroyImmediate (terrainObject);
         Debug.Log ("Terrain Generation Finished.");
     }
 }