Creating variation in grid with random();

Processing Coding Questions
3

Thank you @glv ! Again, this is exactly what I was looking for. When I follow your directions I end up with a black screen after running the code. What am I missing?

int cols, rows;

PVector[][] terrain;

void setup()
  {
  size(1000, 1000);  
  terrain = new PVector [30][30];
  
  cols = 20;  
  rows = 20;
  for (int y = 0; y < rows; y++) 
    {
    for (int x = 0; x< cols; x++) 
      {   
      terrain[x][y] = new PVector(x*50 + random(-5, 5), y*50 + random(-5, 5));
      }
    } 
  noLoop();
  }
  
void draw(){
  background(0);
  stroke(255);
  smooth();
  noFill(); 
  
  translate(width/2, height/2);  //rotate perspective
  translate(-width/2,-height/2); //perspective 
  
  for (int y = 0; y < rows-1; y++) {
    beginShape(QUAD_STRIP); // OR beginShape(QUAD_STRIP), (TRIANGLE_STRIP)
    for (int x = 0; x< cols; x++) {
      //vertex(x*scl, y*scl, terrain[x][y]);
      //vertex(x*scl, (y+1)*scl, terrain[x][y+1]);
      
       }
         endShape();
    }
}