conditional operator in c++

Question

I am confused by the following codes and try to understand what they mean.

 if( (root->left == NULL) || (root->right == NULL) )
 {
    Node *temp = root->left ? root->left : root->right;
 }

it means if root->left ==NULL then temp = root->left? else temp = root->right?

Rakib · Accepted Answer · 2014-06-19T06:15:08.773

5

You are not exactly right, but u get the idea. This is a conditional operator which takes three operands.

 var = condition ? expression1 : expression2

is equivalent to

if( condition )
  var = expression1
else
  var = expression2

In your case it means

if root->left != NULL then temp = root->left, else temp = root->right

instead of

if root->left ==NULL then temp = root->left, else temp = root->right

edited Jun 19 '14 at 06:15

answered Jun 19 '14 at 05:07

Rakib

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The part of the question beginning with "it means..." is wrong (the condition should read `!= NULL`), so saying "you are right" is not correct. – DCoder Jun 19 '14 at 05:47
1

Also, the operator's real name is the *conditional operator*, as in OP's question (see **5.16 Conditional operator [expr.cond]**.) – juanchopanza Jun 19 '14 at 06:01
@DCoder, thanks for correcting me. I overlooked it the `==`operator. – Rakib Jun 19 '14 at 06:08
The ternary operator `?:` returns a value whereas the `if` statement does not. – Tobias Jun 19 '14 at 06:13

score 1 · Answer 2 · answered Jun 19 '14 at 05:26

1

It means the following: If left and right are NULL, then temp equals NULL, otherwise if left is NULL, then temp equals right, otherwise if right is NULL, then temp equals left.

answered Jun 19 '14 at 05:26

ThomasMcLeod

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songyuanyao · Answer 3 · 2014-06-19T05:55:53.257

You're wrong. It means if root->left == NULL then *temp = root->right,
else if root->right == NULL then *temp = root->left,
else *temp will not be set.

There're 4 possible cases:

root->left == NULL and root->right != NULL, *temp will be root->right.
root->left == NULL and root->right == NULL, *temp will be root->right.
root->left != NULL and root->right != NULL, *temp will not be set.
root->left != NULL and root->right == NULL, *temp will be root->left.

Now you can see that 2nd and 3rd case may be potential problem.

conditional operator in c++

3 Answers3