Language: C++

#include <bits/stdc++.h>
//#include <boost/multiprecision/cpp_int.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
#pragma GCC optimize("O3")
#define REP(i,n) for(int i=0;i<n;i++)
#define REPP(i,n) for(int i=1;i<=n;i++)
#define ALL(obj) (obj).begin(), (obj).end()
#define EPS (1e-9)
#define INF (1e17)
#define PI (acos(-1))
//const double PI = acos(-1);
//const double EPS = 1e-15;
//long long INF=(long long)1E17;
#define i_7 (long long)(1e9+7)
//#define i_7 998'244'353
long mod(long a){
    long long c=a%i_7;
    if(c>=0)return c;
    return c+i_7;
}
long long po(long a, long b){
    if(b==0){
        return 1;
    }
    
    long long z = po(a,b/2);
    z = mod(z*z);
    if(b%2!=0){
        z = mod(a*z);
    }
    return z;
}
 
bool prime_(int n){
  if(n==1){
    return false;
  }else if(n==2){
    return true;
  }else{
    for(int i=2;i<=std::sqrt(n);i++){
      if(n%i==0){
        return false;
      }
    }
    return true;
  }
}
 
long long gcd_(long long a, long long b){
  if(a<b){
    std::swap(a,b);
  }
  if(a%b==0){
    return b;
  }else{
    return gcd_(b,a%b);
  }
}
 
long long lcm_(long long x, long long y){
  return (x/gcd_(x,y))*y;
}
 
//using namespace std;
//using namespace boost::multiprecision;
//using namespace __gnu_pbds;

int main(){
  using namespace std;
  int n;
  cin>>n;
  vector<string> a(n);
  REP(i, n) cin>>a[i];
  
  long long b[n];
  REP(i, n){
    string s = a[i];
    if(count(ALL(s), '.') != 0){
      string g;
      while(s.back() != '.'){
        g.push_back(s.back());
        s.pop_back();
      }
      s.pop_back();
      reverse(ALL(g));
      while((int)g.size() < 9) g.push_back('0');
      b[i] = 1000'000'000LL * stoi(s) + stoi(g);
    }else{
      b[i] = 1000'000'000LL * stoi(s);
    }
  }
  
  vector<vector<long long>> cnt(19, vector<long long>(19, 0));
  REP(i, n){
    long long temp = b[i];
    int c = 0, d = 0;
    while(temp % 2 == 0){
      temp /= 2;
      c++;
    }
    while(temp % 5 == 0){
      temp /= 5;
      d++;
    }
    c = min(c, 18); d = min(d, 18);
    cnt[c][d]++;
  }
  
  long long ans = 0;
  int c[2], d[2];
  for(int c[0] = 0; c[0] <= 18; c[0]++){
    for(int d[0] = 0; d[0] <= 18; d[0]++){
      for(int c[1] = 0; c[1] <= 18; c[1]++){
        for(int d[1] = 0; d[1] <= 18; d[1]++){
          
          if(c[0] + c[1] < 18 || d[0] + d[1] < 18) continue;
          
          if(c[0] == c[1] && d[0] == d[1]){
            ans += cnt[c[0]][d[0]] * (cnt[c[0]][d[0]] - 1);
          }else{
            ans += cnt[c[0]][d[0]] * cnt[c[1]][d[1]];
          }
          
        }
      }
    }
  }
  ans /= 2;
  cout << ans << endl;  
  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:112:18: error: array must be initialized with a brace-enclosed initializer
  112 |   for(int c[0] = 0; c[0] <= 18; c[0]++){
      |                  ^
a.cc:113:20: error: array must be initialized with a brace-enclosed initializer
  113 |     for(int d[0] = 0; d[0] <= 18; d[0]++){
      |                    ^
a.cc:114:22: error: array must be initialized with a brace-enclosed initializer
  114 |       for(int c[1] = 0; c[1] <= 18; c[1]++){
      |                      ^
a.cc:115:24: error: array must be initialized with a brace-enclosed initializer
  115 |         for(int d[1] = 0; d[1] <= 18; d[1]++){
      |                        ^