void setup()
{
size(700,700);
}

void draw()
{

for (int i = 0; i < 25; i++)
{
for (int j = 0; j < 25; j++)
{
fill(255,255,255);
rect(i*25,j*25,25,25);
}
}

int fcell = int(random(25));
int scell = int(random(25));
fill(int(random(255)),int(random(255)),int(random(255)));
rect(fcell*25,scell*25,25,25);

}