为什么数字字符的ASCII值等于该值加"0"? [英] Why the ASCII value of a digit character is equal to the value plus '0'?

问题描述

为什么要将数字的ASCII值转换为整数，我们需要这样做:

Why when we want to convert an ASCII value of a digit into an integer, we need to do:

value - '0'?

反之，要将Integer转换为ASCII，我们需要做:

And the other way around, to convert Integer to ASCII, we need to do:

value + '0'

那是为什么?

推荐答案

因为C标准保证数字字符的整数值是连续的.

因此，可以从'1' - '0' == 1，'2' - '0' == 2等推断出您的公式确实有效.

Therefore '1' - '0' == 1, '2' - '0' == 2, etc. from which you can infer that your formulas really do work.

侧注:

1. 由于标准保证了这一点，因此即使目标平台不使用ASCII，它也可以正常工作.
相反，如果该标准没有强制要求这样做(它不对字母值进行强制要求)，则该技术将不可移植.它将取决于使用ASCII的目标系统.

1. Since this is guaranteed by the standard, it works even if the target platform does not use ASCII.
2. Conversely, if the standard did not mandate this (it does not do so with the values of the letters) then this technique would not be portable; it would be dependent on the target system using ASCII.

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