Функция для нахождения суммы факториалов

#include <iostream>
void factorial( int a )
{
int answer = a;
for(int i = a - 1; i > 1; i--)
a *= i;
}
int main()
{
int answer = 0;
for( int i = 1; i <= 9; i++ )
answer += factorial( i );
 
cout << answer;
return 0;
}

answer += factorial( i );

#include <iostream>
using namespace std;
 
int factorial( int a )
{
int answer = a;
for(int i = a - 1; i > 1; i--)
a *= i;
return a;
}
int main()
{
int answer = 0;
for( int i = 1; i <= 9; i++ )
answer += factorial( i );
 
cout << answer;
return 0;
}

#include <iostream>
using namespace std;
 
unsigned long factorial(int a);
 
int main()
{
int answer = 3;
for (int i = 3; i <= 9; i++)
answer += factorial( i );
cout << answer;
cin.get();
return 0;
}
 
unsigned long factorial(int a)
{
unsigned long answer=1;
for (int i=2;i<=a;i++)
answer*=i;
return answer;
}

#include <iostream>
unsigned long long facsum(int a);
 
int main(){
  std::cout << facsum(9);
  std::cin.get();
  return 0;
}
unsigned long long facsum(int a){
  unsigned long long result=2;
  unsigned long long fac=1;
  for (int i=2;i<=a;i++){
    fac*=i;
    result+=fac;
  }
  return result;
}