A definition that takes arguments, particularly more than one, is often known as a macro:
#define SQUARE(x) x * x
Incidentally, the previous definition leads to an interesting problem. What would happen with this line:
y = SQUARE(v + 1);
Because of the literal substitution, what actually gets compiled is y = v + 1 * v + 1;, which algebraically simplifies to y = 2 * v + 1;. Therefore, the macro should be properly define as
#define SQUARE(x) ( (x) * (x) )
Therefore, y = SQUARE(v + 1); becomes y = ( (v + 1) * (v + 1) );.
The rule of thumb is to enclose each argument within the definition in parentheses, which should avoid the issue above.
原来宏定义的时候，会发生这种情况。。。以后定义宏四则运算的时候要注意运算优先级了。
原文地址：http://www.binpress.com/tutorial/learn-objectivec-the-preprocessor/69
原文：http://www.cnblogs.com/kptanjunhao/p/5644337.html