printf help

[pankajkumar911]

int main()
{
char boolean[][6]={"TRUE","FALSE"};
printf("%s",boolean[(unsigned int)-1 == ~0]);
}

i dont understand the (unsigned int)-1== ~0

can any one tell me how it works

[tvrameshmc]

Here (unsigned int)-1 means converting -1 to an equivalent unsigned integer value i.e the max value of unsigned int.

The bitwise complement operator, the tilde, ~, flips every bit.
~0 means all 0 bits are flips to 1 then here also we get same value as above i.e max value of unsigned int.

Finally (unsigned int)-1== ~0 becomes true and it displays

FALSE

.

[Chervil]

The real puzzle is the character string.

    char boolean[][6]={"TRUE","FALSE"};
    printf("%s",boolean[false]);

output:

TRUE

This outputs "TRUE" for a value of false and vice versa.
That's because the bool type can be converted to an integer so that false=0 and true=1. That means the array index for false is zero, meaning the first string, i.e. "TRUE".

To my mind, it would make more sense to initialise the array like this: char boolean[][6]={"FALSE", "TRUE"};

However, this is mixing C++ and C code and maybe there is some reason for original code.