int pos = 50;

void setup()
{
size(250,250);
background(150,150,150);
}

void draw()
{

}

void keyPressed() {

String n = "0123456789";
if (pos == 200) 
{
background(150,150,150);
pos = 50;
}
for (int i = 0; i <= 9;i++)
{

if (keyCode == n.charAt(i))
{
fill(0,0,0);
textSize(25);
text(n.charAt(i), pos,50);
pos += 25;
}
}
}