在条件中使用在do-while循环中声明的变量 [英] Use variables declared inside do-while loop in the condition

问题描述

我在写这样的代码：

do {
    int i = 0;
    int j = i * 2;
    cout<<j;

    i++;
} while (j < 100);

（ http：// codepad.org/n5ym7J5w ）

当我的编译器告诉我，我不能使用变量'j'，因为它不是在do-while循环。

and I was surprised when my compiler told me that I cannot use the variable 'j' because it is not declared outside the do-while loop.

我只是很好奇，如果有任何技术上的原因，为什么这是不可能的。

I am just curious about if there is any technical reason why this cant be possible.

推荐答案

有一个原因，这是不可能的。这是由于语句范围的限制。

There is a reason why this can't be possible. It is due to the limitation of "statement-scope".

您的变量i和j已使用local scope（即{}括号内的变量）声明。你实际上希望j被声明为语句范围，但这是不可能的。

Your variables i and j have been declared with "local scope" -- that is variables inside {} brackets. You actually wanted j to be declared with "statement scope" but this is not possible.

语句范围是声明为'for'，'while' ，'if'或'switch'语句。

Statement-scope are those variables declared as part of 'for', 'while', 'if' or 'switch' statements. Statement scope does not cover do-while statements, though, which is why you cannot do this.

你基本上暴露了使用do-while的语言缺点。

You have basically exposed a language drawback of using do-while.

这将是更好的语言提供：

It would be better if the language offered:

do {
.
.
.
} while (int j < 100);

但不提供此项。

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