foo.cpp: In function 'void gcd(ll, ll, ll&, ll&, ll&)':
foo.cpp:13:22: error: invalid initialization of reference of type 'll& {aka long long int&}' from expression of type 'int'
     gcd(b,a%b,d,x1,y1);
                      ^
foo.cpp:9:6: error: in passing argument 4 of 'void gcd(ll, ll, ll&, ll&, ll&)'
 void gcd(ll a,ll b,ll &d,ll &x,ll &y)
      ^
foo.cpp: In function 'int main()':
foo.cpp:47:30: warning: format '%d' expects argument of type 'int', but argument 2 has type 'll {aka long long int}' [-Wformat=]
         printf("%d\n",(t+b)%b);
                              ^