問題描述
int j=42;
if( (5<j<=1) ) {
printf("yes");
} else {
printf("no");
}
輸出:
yes
為什么輸出yes?
條件不是只對了一半嗎?
Why does it output yes?
Isn't the condition only half true?
推薦答案
C 不理解類似數學的語法，所以
C does not understand math-like syntax, so
if(1<j<=5)
沒有按照您的預期和想要的方式進行解釋；應該是
is not interpreted as you expect and want; it should be
if (1 < j && j <= 5)
或類似的.
正如在其他答案中所解釋的，表達式的計算方式為
As explained in other answers, the expression is evaluated as
((1 < j) <= 5)
=> ("true" <= 5)
=> "true"
其中true"(布爾值)隱式轉換為 1，如 explaneid，例如此處，也參考了標準，這解釋了為什么true"必須是less"比" 5(盡管在 C 中談論從 bool 到 int 的隱式轉換"可能并不完全正確)
where "true" (boolean value) is implicitly converted to 1, as explaneid e.g. here, with references to standards too, and this explain why "true" has to be "less than" 5 (though in C might not be totally correct to speak about "implicit conversion from bool to int")
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