Quality of life is not what you get but what you become

//---------------------------------------------------------------------------
/****************************************************************************
練習6-1：輸入分數，然後印出成績                                             *
****************************************************************************/
#include <iostream>
//---------------------------------------------------------------------------
int grades;
int n=1;

int main(int argc, char* argv[])
{
        std::cout << "Enter grades,system will change it to A~F rank: "
                  << "(not 0-100 = exit) \n";

        for (int i=1;i<=n;i){
          std::cin >> grades;

          if ( grades <= 60 && grades >=0)
            std::cout << "F\n";

          else if ( grades >60 && grades <=70 )
            std::cout << "D\n";

          else if ( grades >70 && grades <=80 )
            std::cout << "C\n";

          else if ( grades >80 && grades <=90 )
            std::cout << "B\n";

          else if ( grades >90 && grades <=100 )
            std::cout << "A\n";

          else
            {std::cout << "You enter the wrong grades";
             break;}
        }
        std::system("pause");
        return 0;
}
//---------------------------------------------------------------------------


題目來源：C++風格與藝術 第二版 Steve Oualline 著 黃吉霈 編譯
答案來源：自我撰寫(不保證正確喔)