哪里錯了呀？？？

//使用while循環
??? while(i<=100)
??? {
??????? i++;
??????? sum+=i*flag;
??????? flag*=-1;
??? }
???
??? i = 1;? //重新初始化變量i
???
??? //do-while循環
??? do{
??????? i++;
??????? sum+=i*flag;
??????? flag*=-1;
??? }while(i<=100);
???
??? i = 1;? //重新初始化變量i
???
??? //使用for循環
??? for(i=1;i<=100;i++)
??? {
??????? sum+=i*flag;
??????? flag*=-1;
??? }?
??? printf("sum=%d\n",sum);
???
??? return 0;???
}