C 语言sizeof运算符

#include<stdio.h>
int main()
{
   int size1 = sizeof ;
   int size2 = sizeof();
   int a = ;
   int size3 = sizeof a;
   int size4 = sizeof(a);
   int size5 = sizeof(int);
   int size7 = sizeof(double);
   //int size6 = sizeof int;//错误写法
   printf("sizeof 10 :%d\n",size1);
   printf("sizeof(10):%d\n",size2);
   printf("sizeof a:%d\n",size3);
   printf("sizeof(a):%d\n",size4);
   printf("sizeof(int):%d\n",size5);
   printf("sizeof(double):%d\n",size7);
   return ;
}

sizeof  :
sizeof():
sizeof a:
sizeof(a):
sizeof(int):
sizeof(double):