/in/foo.c: In function 'main':
/in/foo.c:7:10: error: 'new' undeclared (first use in this function)
  long *a=new long[n];     //动态定义数字a[n]
          ^~~
/in/foo.c:7:10: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:7:14: error: expected ',' or ';' before 'long'
  long *a=new long[n];     //动态定义数字a[n]
              ^~~~
/in/foo.c:13:2: error: 'delete' undeclared (first use in this function)
  delete[] a;              //动态定义出来的最后要释放空间
  ^~~~~~
/in/foo.c:13:9: error: expected expression before ']' token
  delete[] a;              //动态定义出来的最后要释放空间
         ^
/in/foo.c:5:11: warning: unused variable 'b' [-Wunused-variable]
  long n,i,b;
           ^