View Compilation Error

0_0_37983576_12477.cpp: In function 'int main()':
0_0_37983576_12477.cpp:52:24: error: invalid initialization of reference of type 'int&' from expression of type 'long long int'
    gcd_extern(r,mod,a,b); // a r + mod b = 1; s就是a的逆元
                        ^
0_0_37983576_12477.cpp:14:6: note: in passing argument 3 of 'void gcd_extern(int, int, int&, int&)'
 void gcd_extern(int a,int b,int &x,int &y){ // ax + by = gcd(a,b)
      ^