c++第四次作业

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求1000以内所有偶数的和

# include <iostream>    using namespace std;    int main()  {      int i, sum = 0;        i = 2;        do      {          if(i % 2 == 0)          {              sum += i;          }            i++;      }while(i <= 1000);        cout << "sum = " << sum << endl;        return 0;  }

# include <iostream>    using namespace std;    int main()  {      int i, sum = 0;        for(i = 2; i <= 1000; i++)      {          if(i % 2 == 0)          {              sum = sum + i;          }      }        cout << "sum = " << sum << endl;        return 0;  }

# include <iostream>    using namespace std;    int main()  {      int i, sum = 0;        i = 2;        while(i <= 1000)      {          if(i % 2 == 0)          {              sum = sum + i;          }          i++;      }        cout << "sum = " << sum << endl;        return 0;  }

编程序，输出1/3-3/5+5/7-7/9…+19/21的结果

#include<iostream>       #include <cmath>     using namespace std;    int main()    {        double sum=0,i=1,j=3,k=1;      while (i<=19 && j<=21) {  sum=sum+i/j*k;  i+=2;  j+=2;  k=-k;      }      cout<<"1/3-3/5+5/7-7/9…+19/21的结果为："<<sum<<endl;  return 0;         }

乘法口诀表

# include <iostream>  # include <iomanip>  using namespace std;  int main()  {      int i, k, j = 1;      for(k = 1; k < 10; k++)      {          for(i = 1; i <= k; i++)          {              cout << i << "x" << k << "=" << setw(2) << setiosflags(ios::left) << i*k << "  ";          }          j++;          cout << endl;      }      return 0;  }

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