请教，这里的循环结构是怎样的？

#include<stdio.h>   main()   { int x,i; 
  for(i=1;i<=100;i++)   { x=i; 
  if(++x%2==0)   if(++x%3==0)   if(++x%7==0)   printf("%d",x);   } 
  printf("\n");   } 
The output of the program is