非常大数的平方

Question

给定一个 16 位整数。我必须使用位操作或 C++ 中的任何其他方法打印它的平方。我试图将该数字作为 long int 但它不起作用，因为 long int 的范围小于所需的输入。

Answer 1

You can always choose a bigger primitive data type, but often this will just delay the problem. What should you do once you want to take a square of a long long, really?

If you need really big numbers, you need a more abstract, encapsulated data representation. C++ has the right tools to offer for this job, and the Boost libraries make extensive use of them with Boost.Multiprecision . Specifically, look at the documentation for <boost/multiprecision/cpp_int.hpp> . It's complicated, but powerful.

Answer 2

The square is perfectly representable as an unsigned integer (32 bit):

#include <iostream>
#include <cstdint>

int main()
{
    std::int32_t s = (std::int32_t(1) << 16) - 1;
    std::uint32_t u = std::abs(s);
    std::uint32_t square = u * u;
    std::cout << square << " = " << std::hex << square << '\n';
    return 0;
}

Having a signed integer you will face an overflow and get a negative number.