#include<stdio.h>
   int sort(int *p,int len);
   
  int mian()
   {
       int a[10]={0};
      int i,j;
       int len=10;
       printf("please input 10 integer numbers:\n");
      for(i=0;i<len;i++)
         {scanf("%d",&a[i]);}
      sort(a,len);
      for(i=0;i<len;i++)
          {printf("%d",a[i]);}
      printf("\n");
  return 0;
  }
  
  int sort(int *p,int len)
 {
      int i,j,tmp;
      for(i=0;i<len-1;i++)
     {
          for(j=i+1;j<len;j++)
          {
              if(*(p+i)<*(p+j))
              {
                  tmp=*(p+j);
                  *(p+j)=*(p+i);
                  *(p+i)=tmp;
              }
          }
      }
  return *(p+i);
 }
编译时错误提示是：Undefined symbols for architecture x86_64:
  "_main", referenced from:
      start in crt1.10.6.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
这个是什么问题呀，求教？

谢谢。