7章6节for循环计算Fibonacci数

#include <iostream>

unsigned int fib(unsigned int position);
int main()
{
   
 using namespace std;
 unsigned int answer,position;
 
 cout << "Which position? ";
 cin >> position;
 cout << endl;

 answer = fib(position);
 cout << answer << " is the ";
 cout << position << "th Fibonacci number " << endl;

 return 0;
}

unsigned int fib(unsigned int n)
{
 unsigned int minusTwo=1,minusOne=1,answer=2;

 if(n<3)
  return 1;

 for(n-=3 ; n != 0 ; n--)
 {
  minusTwo = minusOne;
  minusOne = answer;
  answer = minusOne + minusTwo;
 }
 return answer;
}