/in/foo.cc:4:1: error: '__int64' does not name a type
 __int64 gcd(__int64 a,__int64 b)
 ^~~~~~~
/in/foo.cc:10:12: error: variable or field 'exgcd' declared void
 void exgcd(__int64 a,__int64 b,__int64 &m,__int64 &n)
            ^~~~~~~
/in/foo.cc:10:12: error: '__int64' was not declared in this scope
/in/foo.cc:10:22: error: '__int64' was not declared in this scope
 void exgcd(__int64 a,__int64 b,__int64 &m,__int64 &n)
                      ^~~~~~~
/in/foo.cc:10:32: error: '__int64' was not declared in this scope
 void exgcd(__int64 a,__int64 b,__int64 &m,__int64 &n)
                                ^~~~~~~
/in/foo.cc:10:41: error: 'm' was not declared in this scope
 void exgcd(__int64 a,__int64 b,__int64 &m,__int64 &n)
                                         ^
/in/foo.cc:10:43: error: '__int64' was not declared in this scope
 void exgcd(__int64 a,__int64 b,__int64 &m,__int64 &n)
                                           ^~~~~~~
/in/foo.cc:10:52: error: 'n' was not declared in this scope
 void exgcd(__int64 a,__int64 b,__int64 &m,__int64 &n)
                                                    ^