在包含三元运算符的表达式中使用方括号 [英] Use of brackets in expression that include ternary operator

问题描述

可能重复：

在下面的代码中，我得到了错误，例如 <需要左值作为赋值的左操作数。我不明白为什么要报告这样的错误。但是，当我在（i> j）？（k = i）:( k = j）这样的表达式中使用括号时，它没有报告错误。

  int main（）{
 int i = 2; 
 int j = 9; 
 int k; 
 
（i> j）？ k = i：k = j; 
 printf（％d\n，k）; 
返回0； 
} 
  

解决方案

很明显，这种情况可以可以用更好的方式重写，但是由于 = 和？：运算符的优先级而引起您的问题。 / p>

赋值运算符？：的优先级高于 = ，因此表达式

 （i> j）？ k = i：k = j; 
  

相当于

 （（（i> j）？k = i：k）= j; 
  

这是不正确的，因为您不能分配给表达式结果。

实际上，这种情况类似于（（i> j）：i：j）= 10; 也不正确。

Possible Duplicate:
Error: lvalue required in this simple C code? (Ternary with assignment?)

In the following piece of code I got an error like "lvalue required as left operand of assignment". I am unable to understand why such an error is being reported. But when I am using parenthesis in the expression like (i>j)?(k=i):(k=j) it is not reporting an error. please explain.

int main() {
    int i = 2;
    int j = 9;
    int k;

    (i>j) ? k=i : k=j;
    printf("%d\n",k);
    return 0;
}

解决方案

It's clear that this condition can be rewritten in a better way, but your problem is observed because of the precedence of = and ?: operators.

The assignment operator ?: has higher precedence than =, thus the expression

( i > j ) ? k = i : k = j;

Is equivalent to

(( i > j ) ? k = i : k) = j;

Which is not correct, because you cannot assign to an expression result.

In fact, this case is similar to (( i > j ) : i : j) = 10; which isn't correct either.

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