是否可以在#define中使用if语句？ [英] Is it possible to use a if statement inside #define?

问题描述

我正在尝试使用以下公式制作一个宏：（a ^ 2 /（a + b））* b ，我想确保没有除以零。

I'm trying to make a macro with the following formula: (a^2/(a+b))*b, and I want to make sure that the there will be no dividing by zero.

#define SUM_A( x, y ) if( x == 0 || y == 0) { 0 } else { ( ( ( x * x ) / ( ( x ) + ( y ) ) ) * ( y ) )}

然后我在main中调用宏：

and then I call the macro inside main:

float a = 40, b = 10, result; 
result = SUM_A(a, b); 
printf("%f", result);

我尝试在if函数周围使用括号，但我在if语句之前一直遇到语法错误。我也尝试过使用return，但是我在某处读到了你不应该在define中使用它。

I've tried using brackets around the if function but I keep getting syntax errors before the if statement. I've also tried using return, but I read somewhere that you're not supposed to use that in define.

推荐答案

你不能使用if语句，因为 #define 是解释由预处理器，输出将是

You can not use if statement, because #define is interpret by the preprocessor, and the output would be

 result=if( x == 0 || y == 0) { 0 } else { ( ( ( x * x ) / ( ( x ) + ( y ) ) ) * ( y ) )}

这是错误的语法。

但另一种方法是使用三元运算符。将您的定义更改为

But an alternative is to use ternary operator. Change your define to

#define SUM_A( x, y )  ((x) == 0 || (y) == 0 ? 0 : ( ( ( (x) * (x) ) / ( ( x ) + ( y ) ) ) * ( y ) ))

请记住始终将您的定义放在括号之间，以避免在替换时出现语法错误。

Remember to always put your define between parentheses, to avoid syntax error when replacing.

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