printfprintf}//output:f 1f {}
The middle operand in a conditional expression may be omitted. Then if the first operand is nonzero, its value is the value of the conditional expression.
Therefore, the expression
has the value of x if that is nonzero; otherwise, the value of y.
This example is perfectly equivalent to
In this simple case, the ability to omit the middle operand is not especially useful. When it becomes useful is when the first operand does, or may (if it is a macro argument), contain a side effect. Then repeating the operand in the middle would perform the side effect twice. Omitting the middle operand uses the value already computed without the undesirable effects of recomputing it.
，要铭记在心;每天都是一年中最美好的日子
