/in/foo.c:7:1: error: unknown type name 'Bigint'
 Bigint d1, d2, ans;
 ^~~~~~
/in/foo.c:7:1: note: use 'struct' keyword to refer to the type
/in/foo.c:8:10: error: unknown type name 'Bigint'
 void Mul(Bigint* p, int x)
          ^~~~~~
/in/foo.c:23:10: error: unknown type name 'Bigint'
 void Add(Bigint* p1, Bigint* p2, Bigint* pans)
          ^~~~~~
/in/foo.c:23:22: error: unknown type name 'Bigint'
 void Add(Bigint* p1, Bigint* p2, Bigint* pans)
                      ^~~~~~
/in/foo.c:23:34: error: unknown type name 'Bigint'
 void Add(Bigint* p1, Bigint* p2, Bigint* pans)
                                  ^~~~~~
/in/foo.c: In function 'main':
/in/foo.c:53:4: error: request for member 'n' in something not a structure or union
  d1.n = 1, d2.n = 1;
    ^
/in/foo.c:53:14: error: request for member 'n' in something not a structure or union
  d1.n = 1, d2.n = 1;
              ^
/in/foo.c:53:10: warning: left-hand operand of comma expression has no effect [-Wunused-value]
  d1.n = 1, d2.n = 1;
          ^
/in/foo.c:54:4: error: request for member 'a' in something not a structure or union
  d1.a[0] = 1, d2.a[0] = 1; 
    ^
/in/foo.c:54:17: error: request for member 'a' in something not a structure or union
  d1.a[0] = 1, d2.a[0] = 1; 
                 ^
/in/foo.c:54:13: warning: left-hand operand of comma expression has no effect [-Wunused-value]
  d1.a[0] = 1, d2.a[0] = 1; 
             ^
/in/foo.c:58:3: warning: implicit declaration of function 'Mul' [-Wimplicit-function-declaration]
   Mul(&d1, x1);
   ^~~
/in/foo.c:61:2: warning: implicit declaration of function 'Add' [-Wimplicit-function-declaration]
  Add(&d1, &d2, &ans);
  ^~~
/in/foo.c:62:14: error: request for member 'n' in something not a structure or union
  for (i = ans.n - 1; i >= 0; i--)
              ^
/in/foo.c:63:19: error: request for member 'a' in something not a structure or union
   printf("%d", ans.a[i]);
                   ^