改程序中哪句是多重定义?

还有其余的逻辑错误和语法错有有哪些.求解
#include

using namespace std;

void main()
{
int count = 0, count1 = 0, count2 = 0, count3 = 0;

 mark = -9;

 while (mark != -9)
 {
     cout << "insert marks of students in your class, enter -9 to stop entering"; 

     cin >> mark;

     count++;

     if (mark >= 0 && mark <= 60);
        count1 = count1 + 1;
     else if (mark >= 61 && mark <= 70);
        count2 = count2 + 1;
     else if (mark >= 71 && mark <= 100);
        count3 = count3 + 1;
  }
  cout <<"Report of MTS3013 course" << endl;
  cout <<"Mark" << count << endl << endl;
  cout << "0-60" << "\t\t\t\t" << count1 << endl;
  cout << "61-70" << "\t\t\t\t" << count2 << endl;
  cout << "71-100" << "\t\t\t\t" << count3 << endl<< endl << endl;
  cout << "End of program";

}

建议如下更改，否则count的值是不对的，把-9也算进去了

#include <iostream>
using namespace std;
void main()
{
    int count = 0, count1 = 0, count2 = 0, count3 = 0;
    int mark=0;
 while (1)
 {
     cout << "insert marks of students in your class, enter -9 to stop entering\n"; 
     cin >> mark;
     if(mark == -9)
         break;
     count++;
     if (mark >= 0 && mark <= 60)
        count1 = count1 + 1;
     else if (mark >= 61 && mark <= 70)//;
        count2 = count2 + 1;
     else if (mark >= 71 && mark <= 100)//;
        count3 = count3 + 1;
  }
  cout <<"Report of MTS3013 course" << endl;
  cout <<"Mark " << count << endl << endl;
  cout << "0-60" << "\t\t\t\t" << count1 << endl;
  cout << "61-70" << "\t\t\t\t" << count2 << endl;
  cout << "71-100" << "\t\t\t\t" << count3 << endl<< endl << endl;
  cout << "End of program";
}

代码修改如下：（问题在代码中标注）

#include <iostream>

using namespace std;

void main()
{
    int count = 0, count1 = 0, count2 = 0, count3 = 0;

    int mark = -9; //修改1，添加变量类型

    while (1)
    {
        cout << "insert marks of students in your class, enter -9 to stop entering"; 

        cin >> mark;
                if(mark ==－9) break;

        count++;

        if (mark >= 0 && mark <= 60)//; //这里多了一个分号
        count1 = count1 + 1;
        else if (mark >= 61 && mark <= 70)//;//这里多了一个分号
        count2 = count2 + 1;
        else if (mark >= 71 && mark <= 100)//;//这里多了一个分号
        count3 = count3 + 1;
    }
    cout <<"Report of MTS3013 course" << endl;
    cout <<"Mark" << count << endl << endl;
    cout << "0-60" << "\t\t\t\t" << count1 << endl;
    cout << "61-70" << "\t\t\t\t" << count2 << endl;
    cout << "71-100" << "\t\t\t\t" << count3 << endl<< endl << endl;
    cout << "End of program";
}

#include <iostream>
using namespace std;

void main()
{
    int count = 0, count1 = 0, count2 = 0, count3 = 0;

    int mark=0;//mark = -9;缺少类型，并且初始化不能为-9，否则不执行循环
 
 while (mark != -9)
 {
     cout << "insert marks of students in your class, enter -9 to stop entering\n"; 
 
     cin >> mark;
 
     count++;
 
     if (mark >= 0 && mark <= 60)//;多个个分号，下同
        count1 = count1 + 1;
     else if (mark >= 61 && mark <= 70)//;
        count2 = count2 + 1;
     else if (mark >= 71 && mark <= 100)//;
        count3 = count3 + 1;
  }
  cout <<"Report of MTS3013 course" << endl;
  cout <<"Mark" << count << endl << endl;
  cout << "0-60" << "\t\t\t\t" << count1 << endl;
  cout << "61-70" << "\t\t\t\t" << count2 << endl;
  cout << "71-100" << "\t\t\t\t" << count3 << endl<< endl << endl;
  cout << "End of program";
}