why it prints 3?

sam_psycho

Can anybody tell me why value of b is 3 in this code? what happens with (a=0) exactly?

int a=0;
int b=(a=0)?2:3;
cout<

David Crow

Because the statement within parenthesis, which assigns 0 to a, equates to 0 (false), thus assigning 3 to b. If you change it to:

int b = (a = 1) ? 2 : 3;

it might make more sense.

"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

CPallini

The result of the expression (assignment)

(a=0)

is 0, i.e. the value of a (that is false for the conditional operator ?). hence the result of the expression

VCD_A wrote:

(a=0)?2:3

is 3. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

CPallini

DavidCrow wrote:

change it to: int b = (a = 1) ? 2 : 3; it might make more sense.

Does it really make more sense? :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

David Crow

In that it would instead assign 2 to b, yes.

"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

CPallini

Ah, OK, it makes a lot more sense... :-D

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Stuart Dootson

a=0 is assignment. You probably wanted a==0 (two = signs), which is hte equality test. One of the things that's nice (when you're experienced), yet horrible (when you're learning) about C and C++ is that assignment is an expression, not a statement, which means that you can do what you've done there. In other languages like Ada, which class assignment as a statement, you couldn't make that mistake.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

sam_psycho

but if your are assigning any thing to any variable(in our case a=0), this statement suppose to a true, and a=1 does, but what is wrong with zero?

_Superman_

In C (and C++) 0 equates to false and non-zero equates to true. The case that you mentioned is similar to

int a = 0;
if (a)
{
b = 2;
}
else
{
b = 3;
}

Since a is 0, this equates to if(0) or if(false). So the else part will be executed. But in the following snippet, the if part will be executed.

int a = -1;
if (a)
{
b = 2;
}
else
{
b = 3;
}

«_Superman_» I love work. It gives me something to do between weekends.

Lost User

The result of assignment is the value that was assigned to the lvalue, not some sort of status flag indicating that the assignment succeeded. The result of a=x is x, thus a=0 equals 0.

David Crow

VCD_A wrote:

but if your are assigning any thing to any variable(in our case a=0), this statement suppose to a true...

So what would you propose the value of a and b to be in the following:

int a, b, c;
a = b = c = 5;

Hint: it's not 1.

"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons