如何在这种情况下，数组索引工作性质再presentation？ [英] How does character representation in array index work in this case?

问题描述

我在C初学者，我有code是这样的：

I'm a beginner in C and I have code like this :

#include <stdio.h>
main()
{
    int i;
    int ndigit[10] = { [9] = 5 };
    printf("%d\n",++ndigit['9']);
}

本打印的价值是这样的：

This prints the value something like this :

-1074223011

但是，当我改变语句：

But when I change the statement to:

++ndigit['9'-'0']

这是正确打印值

6

我不知道为什么有必要添加 -0 在我的指数，使其正常工作？又为什么只是提 ++ ndigit ['9'] ，并不能帮助我？

I wonder why there is a need for adding -0 in my index to make it work properly? And why just mentioning ++ndigit['9'], doesn't help me?

先谢谢了。

推荐答案

如果您要访问的第10个数组中的元素，你做的：

If you want to access the 10th element in an array, you do:

array[9]

如果你想拥有的字符常量数的值索引来访问元素 9 + 1，你做的：

If you want to access the element at the index which has the value of the character constant for the number 9 + 1, you do:

array['9']

由于方式ASCII（用C使用，其他所有字符编码方案，看绿野仙踪的评论）的定义，前pression '9' - '0'实际上等于9，这可能会迷惑你在这种情况下。

Due to the way ASCII (and all other character encoding schemes used by C, see Wiz's comment) is defined, the expression '9' - '0' actually equals 9, which might confuse you in this case.

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