Obviously, the 0 should be at the left edge of the ruler, but if we place the two - and three-digit Numbers at the 72-pixel points, they will appear unbalanced.
In subtraction, one never "carries" a digit or bit on to the next left place-weight.
在减法，一个从来没有“携带”数字或比特的下一个离开的地方体重。
3
You can use [: digit:] in place of [0-9], and [: alpha:] is a more portable replacement for [-a-za-z0-9_]. For example, you can strip all punctuation from a string by using the statement.
您可以使用[：digit：]代替[0 - 9]，并且[：alpha：]是比[- a - zA - z 0 - 9 _]更具有可移植性的替代者。