Please tell me why this condition is always true

Question

enum bool{true,false};
void main()
{
    if(true==(2==3))
    {
        printf("true\n");
    }
    else
    {
        printf("false\n");
    }

    return 0;
}

Answer 1

The enum true is 0 in this case.

so:

0==(2==3)
0==(0)
1

1 is true. Thus this conditional is always true.

Answer 2

It's because the default starting point for enums in C is 0, which happens to be false, not true.

You should use enum bool {false, true} instead. And please don't use abominations like

if (x == true)
if (x == false)

at all. You'd be better off with

if (x)
if (!x)

By all means, use true and false for setting booleans but you should never have to test them that way. Especially since the definition is zero/non-zero, not zero/one.

I've always liked (if you really have to):

#define false (1==0)
#define true  (1==1)

That's at least guaranteed to work.

Answer 3

In your enumeration, true has the constant value 0, and false has the constant value 1.

In C, the result of an equality comparison (2==3) is either 0 for not equal, or 1 for equal. Your code is:

if ( 0 == (2==3) )

or

if ( 0 == 0 )

Which is clearly true.

Answer 4

Defining the enums 'true' and 'false' is a bad idea anyway. In C, 'false' is zero, and 'true' is non-zero... true is not necessarily '1'.

Answer 5

Because true is false and false is true.