语法和“< letter>”的不同含义 [英] Syntax and different meanings of '<letter>'

问题描述

我正在从K& R书中学习C，并且碰到了代码以计算否。空格字符（空白，制表符，换行符）和所有其他字符的出现。

代码如下：

I am learning C from the K&R book and I came across the code to count the no. of occurrence of white space characters (blank, tab, newline) and of all other characters.
The code is like this:

#include <stdio.h>
/* count digits, white space, others */
main()
{
    int c, i, nwhite, nother;
    int ndigit[10];  
    nwhite = nother = 0;
    for (i = 0; i < 10; ++i)
        ndigit[i] = 0;
    while ((c = getchar()) != EOF)
        if (c >= '0' && c <= '9')
            ++ndigit[c-'0'];
        else if (c == ' ' || c == '\n' || c == '\t')
            ++nwhite;
        else
            ++nother;
    printf("digits =");
    for (i = 0; i < 10; ++i)
        printf(" %d", ndigit[i]);
    printf(", white space = %d, other = %d\n",
    nwhite, nother);
}

我需要问2个问题。.

1st问题：

I need to ask 2 questions..
1st question:

if (c >= '0' && c <= '9')
++ndigit[c-'0']; 

我很清楚， 0和 9表示ASCII值0& 9个。但是我似乎不明白的是，为什么我们甚至需要使用ASCII谷值而不是整数本身。就像为什么我们不能简单地使用

I very well know that '0' and '9'represents the ASCII value of 0 & 9 respectively. But what I don't seem to understand is why we even need to use the ASCII vale and not the integer itself. Like why can't we simply use

if (c >= 0 && c <= 9)

查找c是否在0到9之间？

to find if c lies between 0 and 9?

第二个问题：

++ndigit[c-'0']

上面的语句是做什么的？

为什么我们不在这里取c的ASCII值？

因为如果这样做，它应该被写为 ['c'-'0'] 。

What does the above statement do?
Why aren't we taking the ASCII value of c here?
Because if we did, it should have been written as ['c'-'0'].

推荐答案

1. getchar（）返回字符代码和标记值（EOF）。因此，我们知道 c 在循环内保存了字符代码。

1. getchar() returns character codes and sentinel values (EOF). So, we know c holds a character code inside the loop.

c-'0'是字符代码数字行上从c值（字符代码）到 0代码的距离。根据C标准，字符代码必须以连续的顺序'0'，'1，'2'，'3'，'4'，'5'，'6'，'7'，'8'， '9'。因此，该表达式将计算数字字符的整数值。

c-'0' is the distance on the character code "number line" from the value of c (a character code) to the code for '0'. Per the C standard, character codes must have these digits in consecutive order '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'. So, the expression computes the integer value of the digit character.

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