How can I calculate the tens place value of 2^100 in C ?

I tried this;

#include <cmath>
#include <iostream>

using namespace std;

int main(){
    int answer;
    answer=(unsigned long long int)pow(2, 100)0/10;//zero
    cout<<answer<<endl;
    return 0;
}

But it printed 0 because of overflow.

Python prints the answer correctly with this code;

print(2**1000//10)

But how do I calculate it in C ?

CodePudding user response：

Just do it in 2 steps:

int x = (1<<25)0;
x = (x*x*x*x)0;
x = x/10;

CodePudding user response：

unsigned long long int is not large enough to store 2**100. If you are using GCC or Clang, try to use __int128 instead.

#include <cmath>
#include <cstdint>
#include <iostream>
int main(int argc, char **argv) {
  int answer = ((__int128)std::pow(2, 100)) % 100 / 10;
  std::cout << answer << '\n'; // 7
}

CodePudding user response：

You have a problem with typecasting.

As you can see from documentation std::pow return double

So first step to solve our problem, try to remove type casting.

std::pow(2, 100); // return 1.26765e 30

The next problem we can't use operator% with double type so we need std::fmod So final solution would look like this:

int answer= std::fmod(std::pow(2, 100), 100) / 10;