How to extract the bits from a binary number?

[baby bunny]

Hi,

I want a function that, given two integers n and k, returns the kth bit of the binary representation of n. Does C++ come with such a function? If yes, which library do I need? Thanks!

[Chervil]

You just need to "and" the number n with an integer with just the required bit set on, like this: n & (1<<k)

Or consider the following:

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#include <iostream> using namespace std; int getBit(int n, int k) { return (n & (1<<k)) != 0; } int main() { int n = 141; for (int k = 31; k>=0; k--) cout << getBit(n,k); cout << endl; return 0; }

00000000000000000000000010001101

[baby bunny]

Wow thanks! And could you tell me how & and << works? I've never learned them. I just searched the this site but didn't find their definition.

[Chervil]

In this context, << is the bitwise shift-left operator. It moves the integer (in its binary representation) one position to the left.

If you're not familiar with the operators, then you should take a look at the tutorial pages:
http://www.cplusplus.com/doc/tutorial/operators/

I'd also suggest looking here, as it gives more detail:
http://www.cprogramming.com/tutorial/bitwise_operators.html

[baby bunny]

Thanks a lot!