/in/foo.cc:8:1: error: '__int64' does not name a type
 __int64 EXTENDED_EUCLID(__int64 a,__int64 b,__int64& x,__int64& y)
 ^~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:25:2: error: '__int64' was not declared in this scope
  __int64 A,B,C,k;
  ^~~~~~~
/in/foo.cc:26:41: error: 'A' was not declared in this scope
  while(scanf("%I64d %I64d %I64d %I64d",&A,&B,&C,&k))
                                         ^
/in/foo.cc:26:44: error: 'B' was not declared in this scope
  while(scanf("%I64d %I64d %I64d %I64d",&A,&B,&C,&k))
                                            ^
/in/foo.cc:26:47: error: 'C' was not declared in this scope
  while(scanf("%I64d %I64d %I64d %I64d",&A,&B,&C,&k))
                                               ^
/in/foo.cc:26:50: error: 'k' was not declared in this scope
  while(scanf("%I64d %I64d %I64d %I64d",&A,&B,&C,&k))
                                                  ^
/in/foo.cc:31:11: error: expected ';' before 'a'
   __int64 a=C;
           ^
/in/foo.cc:32:11: error: expected ';' before 'b'
   __int64 b=B-A;
           ^
/in/foo.cc:33:11: error: expected ';' before 'n'
   __int64 n=(__int64)1<<k;  //2^k
           ^
/in/foo.cc:34:11: error: expected ';' before 'x'
   __int64 x,y;
           ^
/in/foo.cc:35:11: error: expected ';' before 'd'
   __int64 d=EXTENDED_EUCLID(a,n,x,y);  //求a,n的最大公约数d=gcd(a,n)和方程d=ax+by的系数x、y
           ^
/in/foo.cc:37:6: error: 'b' was not declared in this scope
   if(b%d!=0)  //方程 ax=b(mod n) 无解
      ^
/in/foo.cc:37:8: error: 'd' was not declared in this scope
   if(b%d!=0)  //方程 ax=b(mod n) 无解
        ^
/in/foo.cc:41:4: error: 'x' was not declared in this scope
    x=(x*(b/d))%n;  //方程ax=b(mod n)的最小解
    ^
/in/foo.cc:41:16: error: 'n' was not declared in this scope
    x=(x*(b/d))%n;  //方程ax=b(mod n)的最小解
                ^