I have a task to practice and I just can't get the solution. It should be noted that I am a total beginner. There is 1min for the exercise, so it should be child's play. But I am racking my brains over it.

I am supposed to write an expression for the following :

Let x and k be variables of type int. Formulate a C condition with bitwise operator that is true exactly when x is less than 2^(k-1).

I would have done this with the ?-operator. So something like

( ) ? 1 : 0

But which condition must be in the brackets? I can't think of a bitwise operator that can be used to compare less than?

I really don't have any Idea :/

CodePudding user response：

It seems you mean something like the following

if ( x < 1 << k - 1 ) { /*...*/ }

provided that the expression k - 1 is not negative and the expression 1 << k - 1 is representable as a positive value in an object of the type int.

CodePudding user response：

Let x and k be variables of type int.

int x;
int k;

Formulate a C condition with bitwise operator that is true exactly when x is less than 2^(k-1).

Start with directly translating it:

if ( x < pow(2,k-1) ) { ... }

Then remove the call to pow using bitwise operators

2-to-the-power-of k-1 is: 1<<(k-1)

Examples: to help clarify

2 ^ 3 == 1 << 3 == 8
2 ^ 5 == 1 << 5 == 32

So the final expression is:

( x < 1<<(k-1) ); // Result will either be 1 or 0

There is no need to use ternary ?: operator.
The boolean expression < will evaluate to 1 or 0 by itself!