c++ - 如果没有条件？

Question

我今天才发现这个“C++”，但我无法理解它:

if(array[i][j]) {--i;--j;}

谁能给我解释一下这是怎么回事？我只是不明白。这里的条件是什么？似乎每次都是如此，但是当我摆脱 IF 时(所以只剩下这个 {--i;--j;}。)它的工作原理就不一样了。

我是 C++ 的新手，所以请轻松阅读解释! :)

谢谢!

Answer 1

在 C++ 中，非零值可用于在条件语句中指示“成功”。

这是来自 C99，第 6.8.4.1 节:

The if Statement

2 In both forms, the first substatement is executed if the expression compares unequal to 0.

来自 C++03，第 6.4 节

4 The value of a condition that is an initialized declaration in a statement other than a switch statement is the value of the declared variable implicitly converted to type bool. If that conversion is ill-formed, the program is ill-formed. The value of a condition that is an initialized declaration in a switch statement is the value of the declared variable if it has integral or enumeration type, or of that variable implicitly con- verted to integral or enumeration type otherwise. The value of a condition that is an expression is the value of the expression, implicitly converted to bool for statements other than switch; if that conversion is ill-formed, the program is ill-formed. The value of the condition will be referred to as simply “the condi- tion” where the usage is unambiguous.

bool 转换定义在6.3.1.2

6.3.1.2 Boolean type

1 When any scalar value is converted to _Bool, the result is 0 if the value compares equal to 0; otherwise, the result is 1.

而int是一个标量类型。我假设这就是你的数组填充的内容，因为你可以在它们上使用一元 ++ 和 --。