for loop

A for loop repeats the same code a certain number of times.

for loop 会让电脑按照设定的次数，重复执行同一段代码。

while loop

A while loop keeps repeating while a condition is true.

infinite loop 无限循环

I first thought c = 0 means c will always stay 0, but now I understand that c++ changes its value every time the loop runs.

for loop

is useful when I already know how many times I want to repeat something.

while loop

continues as long as a condition is true.

Nested if

比如 hover 后：

左边变蓝，右边变红。

if (mouseX > c * 20 && mouseX < c * 20 + 20) {

  if (c < 10) {
    fill(0, 0, 255);
  } else {
    fill(255, 0, 0);
  }

} else {
  fill(255);
}

这里有两层判断：

第一层：

Is the mouse hovering over this column?

鼠标有没有在这个 column 上？

第二层：