let c = 10;   

let r = 10;        

function setup() {

  createCanvas(400,400);

}

​

function draw() {

  background(220);

  let cellwidth = width/ c;    

  let cellheight = height / r;  

​

  for (let lc = 0; lc < c; lc++) { // Loop through columns

    for (let lr = 0; lr < r; lr++) { // Loop through rows

      let x = lc * cellwidth;      

      let y = lr * cellheight;     

      if ((lc + lr) % 2 === 0) { //even and odd

        fill("black");

      } else {

        fill("white");

      }

      rect(x, y, cellwidth, cellheight); 

    }

  }

}

​