比较 if 语句中的 3 个参数时无法理解第一个代码的输出
这是一个小代码，一次性比较 3 个变量。我比较了2个代码。
FIRST
#include <iostream>
int main() {
if( 8 > 7 > 6) std::cout << "true";
else std::cout << "false";
std::cout << "\n";
std::cout << (8 < 9);
std::cout << "\n";
system("pause");
}
// output :
/* false
* 1
*/
SECOND
#include <iostream>
int main() {
if( 8 > (7 > 6) ) std::cout << "true"; // with brackets
else std::cout << "false";
std::cout << "\n";
std::cout << (8 < 9);
std::cout << "\n";
system("pause");
}
// output :
// true
// 1
我理解第二个输出，但无法理解第一个代码中的 if 语句是如何计算的？
请解释一下。
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评论（8）
关系运算符是从左到右的，因此
8>7>6的计算结果为 (8>7)>6。8>7计算结果为true，它会转换为1，因此您会得到1>6，即假。C++标准其实明确提到了这一点：
The relational operators are left-to-right, so
8>7>6gets evaluated as (8>7)>6.8>7evaluates totrue, which is converted to1, so you get1>6, which isfalse.The C++ standard actually mentions this point explicitely:
if( 8 > 7 > 6)表示if( (8 > 7) > 6)表示if( (1) > 6 )表示if(false)。这意味着，if块无法执行，else块将被执行，并打印false。if( 8 > (7 > 6))表示if( ( 8 > (1) )表示if(true)因此，执行if块会打印true，如果您知道
(8<9)的值，就很容易知道是什么。 ><的意思是。(8<9)返回true，这意味着1。if( 8 > 7 > 6)meansif( (8 > 7) > 6)which meansif( (1) > 6)which meansif(false). That means,ifblock cannot execute,elseblock will be executed which printsfalse.if( 8 > (7 > 6))meansif( ( 8 > (1) )which meansif(true). Soifblock gets executed which printstrue.And the value of
(8<9)is easy to know if you know what<means. Well,(8<9)returnstruewhich means1.第一个代码的 if 语句按从左到右的顺序进行计算。即：
(8 > 7) > 6计算如下：请注意，
(8 > 7)为true，因此它返回与true等价的数值>，<代码>1。总体评价为
0，即。假。The first code's if statement is evaluated in left-to-right order. ie:
(8 > 7) > 6which is evaluated as follows:Note that
(8 > 7)istrue, so it returns the numerical equivalent fortrue,1.The overall evaluation comes to
0, ie.false.if 语句通常用于比较 2 个语句，如果您想要比较 2 个以上的语句，您应该使用布尔 OR
||或布尔 AND&&.这背后的推理基于布尔逻辑。您在第一个程序中发布的语句从左到右计算，这意味着如果 8 大于 7（确实如此），它将计算为 true，即布尔逻辑中的“1”（1 为 true，0 为 false）。
因此，在评估之后，你有：
自然评估为 false。因为比较不再是 8/7/6，而是 true / 6。在这种情况下，true 小于 6，因此为 false。
如果你像这样设置它，就会得到预期的结果：
或者，如果你想详尽无遗..
那么所有数字都会被比较（如果你有 3 个变量，这会更明智，也许在哪里x 应等于 100，y 应等于 50，z 应等于 25。）
然后您将进行比较
如果您的变量具有您期望的内容，则该比较将评估为 true。
An if statement is classically made to compare 2 statements, if you are wanting to compare more than 2 statements you should be using a boolean OR
||or a boolean AND&&. The reasoning behind this is based in boolean logic. The statement that you posted in the first program evaluates from left to right meaningIf 8 is greater than 7 (which it is) it will evaluate to true, which is "1" in boolean logic (1 being true, 0 being false).
Thus after that evaluates you have:
which naturally evaluates to false. Because the comparison is no longer 8/7/6, it's true / 6. And in this case, true is less than 6, thus a false.
If you were to set it up like this, would would have the expected results:
or alternatively, if you wanted to be exhaustive..
so all numbers are compared (this would be more sensible in the event that you had 3 variables, perhaps where x should be equal to 100, y should be equal to 50, and z should be equal to 25.)
You'd then have the comparison
This would evaluate to true in the event that your variables had the contents that you expected.
if(8 > 7 > 6) 的计算方式如下：
if(8 > 7 > 6) is evaluated like :
if 语句从左到右计算，因此与 (8>7)>6 相同。
8>7 为真，等于 1，因此它评估 1>6，为假。
The if statement is evaluated left to right so it is the same as (8>7)>6.
8>7 is true which is equal to 1 so then it evaluates 1>6 which is false.
关系运算符从左到右关联！
8>7>6 = (8>7)>6 = 1>6 = 假
The relational operators associate from left to right!
8>7>6 = (8>7)>6 = 1>6 = FALSE
运算符“>”的结合性是从左到右，所以这意味着在第一个示例中，首先评估“8 > 7”，其结果为 1，然后针对 6 评估，结果为 false。
在第二个示例中，由于您使用括号，因此我们有 8 > 1，这是真的。
希望这有帮助。
The associativity of operator ">" is from left to right, so it means that in your first example, "8 > 7" is evaluated first, and the result of that is 1, which is then evaluated against 6, which result is false.
In the second example, since you use brackets, the we have 8 > 1, which is true.
Hope this helps.