foo.c:8:13: error: unknown type name 'BigInt'; did you mean 'int'?
 void Output(BigInt *p);
             ^~~~~~
             int
foo.c:9:10: error: unknown type name 'BigInt'; did you mean 'int'?
 void Mul(BigInt *p, int x);
          ^~~~~~
          int
foo.c:10:13: error: unknown type name 'BigInt'; did you mean 'int'?
 int Compare(BigInt *p1, BigInt *p2);
             ^~~~~~
             int
foo.c:10:25: error: unknown type name 'BigInt'; did you mean 'int'?
 int Compare(BigInt *p1, BigInt *p2);
                         ^~~~~~
                         int
foo.c:11:10: error: unknown type name 'BigInt'; did you mean 'int'?
 void Add(BigInt *p1,BigInt *p2, BigInt *pAns);
          ^~~~~~
          int
foo.c:11:21: error: unknown type name 'BigInt'; did you mean 'int'?
 void Add(BigInt *p1,BigInt *p2, BigInt *pAns);
                     ^~~~~~
                     int
foo.c:11:33: error: unknown type name 'BigInt'; did you mean 'int'?
 void Add(BigInt *p1,BigInt *p2, BigInt *pAns);
                                 ^~~~~~
                                 int
foo.c: In function 'main':
foo.c:19:2: error: unknown type name 'BigInt'; use 'struct' keyword to refer to the type
  BigInt y1;
  ^~~~~~
  struct 
foo.c:20:4: error: request for member 'n' in something not a structure or union
  y1.n=1; y1.digit[0]=1;  
    ^
foo.c:20:12: error: request for member 'digit' in something not a structure or union
  y1.n=1; y1.digit[0]=1;  
            ^
foo.c:21:23: warning: implicit declaration of function 'Mul' [-Wimplicit-function-declaration]
  for(i=1; i<=n1; i++) Mul(&y1,x1); 
                       ^~~
foo.c:23:2: error: unknown type name 'BigInt'; use 'struct' keyword to refer to the type
  BigInt y2;
  ^~~~~~
  struct 
foo.c:24:4: error: request for member 'n' in something not a structure or union
  y2.n=1; y2.digit[0]=1;   
    ^
foo.c:24:12: error: request for member 'digit' in something not a structure or union
  y2.n=1; y2.digit[0]=1;   
            ^
foo.c:26:2: error: unknown type name 'BigInt'; use 'struct' keyword to refer to the type
  BigInt y3;
  ^~~~~~
  struct 
foo.c:27:2: warning: implicit declaration of function 'Add' [-Wimplicit-function-declaration]
  Add(&y1, &y2, &y3);
  ^~~
foo.c:28:2: warning: implicit declaration of function 'Output' [-Wimplicit-function-declaration]
  Output(&y3);
  ^~~~~~
foo.c: At top level:
foo.c:31:10: error: unknown type name 'BigInt'; did you mean 'int'?
 void Add(BigInt *p1,BigInt *p2, BigInt *pAns)
          ^~~~~~
          int
foo.c:31:21: error: unknown type name 'BigInt'; did you mean 'int'?
 void Add(BigInt *p1,BigInt *p2, BigInt *pAns)
                     ^~~~~~
                     int
foo.c:31:33: error: unknown type name 'BigInt'; did you mean 'int'?
 void Add(BigInt *p1,BigInt *p2, BigInt *pAns)
                                 ^~~~~~
                                 int
foo.c:57:13: error: unknown type name 'BigInt'; did you mean 'int'?
 int Compare(BigInt *p1, BigInt *p2)
             ^~~~~~
             int
foo.c:57:25: error: unknown type name 'BigInt'; did you mean 'int'?
 int Compare(BigInt *p1, BigInt *p2)
                         ^~~~~~
                         int
foo.c:67:10: error: unknown type name 'BigInt'; did you mean 'int'?
 void Mul(BigInt *p, int x)
          ^~~~~~
          int
foo.c:83:13: error: unknown type name 'BigInt'; did you mean 'int'?
 void Output(BigInt *p)
             ^~~~~~
             int
foo.c: In function 'main':
foo.c:16:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&x1,&n1);
  ^~~~~~~~~~~~~~~~~~~~~~
foo.c:17:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&x2,&n2);
  ^~~~~~~~~~~~~~~~~~~~~~

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