/in/foo.c:7:10: error: unknown type name 'BigInt'
 void Mul(BigInt *p, int x);
          ^~~~~~
/in/foo.c:8:10: error: unknown type name 'BigInt'
 void Add(BigInt *p1,BigInt *p2, BigInt *p3);
          ^~~~~~
/in/foo.c:8:21: error: unknown type name 'BigInt'
 void Add(BigInt *p1,BigInt *p2, BigInt *p3);
                     ^~~~~~
/in/foo.c:8:33: error: unknown type name 'BigInt'
 void Add(BigInt *p1,BigInt *p2, BigInt *p3);
                                 ^~~~~~
/in/foo.c:9:13: error: unknown type name 'BigInt'
 void OutPut(BigInt * p);
             ^~~~~~
/in/foo.c: In function 'main':
/in/foo.c:14:2: error: unknown type name 'BigInt'
  BigInt x1;
  ^~~~~~
/in/foo.c:14:2: note: use 'struct' keyword to refer to the type
/in/foo.c:15:4: error: request for member 'digit' in something not a structure or union
  x1.digit[0] = 1;x1.n = 1;
    ^
/in/foo.c:15:20: error: request for member 'n' in something not a structure or union
  x1.digit[0] = 1;x1.n = 1;
                    ^
/in/foo.c:19:3: warning: implicit declaration of function 'Mul' [-Wimplicit-function-declaration]
   Mul(&x1,m1);
   ^~~
/in/foo.c:20:2: error: unknown type name 'BigInt'
  BigInt x2;
  ^~~~~~
/in/foo.c:20:2: note: use 'struct' keyword to refer to the type
/in/foo.c:21:4: error: request for member 'digit' in something not a structure or union
  x2.digit[0] = 1;x2.n = 1;
    ^
/in/foo.c:21:20: error: request for member 'n' in something not a structure or union
  x2.digit[0] = 1;x2.n = 1;
                    ^
/in/foo.c:24:2: error: unknown type name 'BigInt'
  BigInt x3;
  ^~~~~~
/in/foo.c:24:2: note: use 'struct' keyword to refer to the type
/in/foo.c:25:2: warning: implicit declaration of function 'Add' [-Wimplicit-function-declaration]
  Add(&x1,&x2,&x3);
  ^~~
/in/foo.c:26:2: warning: implicit declaration of function 'OutPut' [-Wimplicit-function-declaration]
  OutPut(&x3);
  ^~~~~~
/in/foo.c: At top level:
/in/foo.c:30:10: error: unknown type name 'BigInt'
 void Add(BigInt *p1,BigInt *p2, BigInt *p3)
          ^~~~~~
/in/foo.c:30:21: error: unknown type name 'BigInt'
 void Add(BigInt *p1,BigInt *p2, BigInt *p3)
                     ^~~~~~
/in/foo.c:30:33: error: unknown type name 'BigInt'
 void Add(BigInt *p1,BigInt *p2, BigInt *p3)
                                 ^~~~~~
/in/foo.c:60:10: error: unknown type name 'BigInt'
 void Mul(BigInt *p, int x)
          ^~~~~~
/in/foo.c:77:13: error: unknown type name 'BigInt'
 void OutPut(BigInt *p)
             ^~~~~~