在C和C ++中1LL或2LL是什么？

Question

I was looking at some of the solutions in Google Code Jam and some people used this things that I had never seen before. For example,

2LL*r+1LL

What does 2LL and 1LL mean?

Their includes look like this:

#include <math.h>
#include <algorithm>
#define _USE_MATH_DEFINES

or

#include <cmath>

Answer 1

The LL makes the integer literal of type long long .

So 2LL , is a 2 of type long long .

Without the LL , the literal would only be of type int .

This matters when you're doing stuff like this:

1   << 40
1LL << 40

With just the literal 1 , (assuming int to be 32-bits, you shift beyond the size of the integer type -> undefined behavior). With 1LL , you set the type to long long before hand and now it will properly return 2^40.