📅  最后修改于: 2022-03-11 14:44:45.985000             🧑  作者: Mango
The part str[i] - '0' takes the ASCII character of the corresponding digit
which are sequentially "0123456789" and subtracts the code for '0' from the
current character. This leaves a number in the range 0..9 as to which digit is
in that place in the string.