这条线返回什么？

Question

int lf = ((t.left==null) = (t.right==null)) ? 1:0;

如果大括号中的语句为true，则返回1，但是在中间，为lefT分配正确的值有什么意义呢？

Answer 1

Normally you'd have an equal sign to assign. The return of the assigned is the same as the RHS of the expression.

You'd use an equal sign in a expression within an if to assign and check the result at the same time.

// return first and third items added if they exist.
if ((list = GetItems()).Length > 2) { return list[0] + list[2]; } 

Right here all you have is a compiler error because t.left==null evaluates to (true/false) and you can't assign to that.

Answer 2

If both t.left and t.right are either null or not null at the same time , then lf is 1 otherwise it is 0 .

Also you have a typo in there. The line should be

int lf = ((t.left==null) == (t.right==null)) ? 1:0;

Notice the == between the two null checks.