/in/foo.c:5:24: error: expected ';', ',' or ')' before '&' token
 ll exgcd(ll a, ll b, ll& x, ll& y) {
                        ^
/in/foo.c: In function 'main':
/in/foo.c:15:9: warning: implicit declaration of function 'exgcd' [-Wimplicit-function-declaration]
     g = exgcd(a, l, x, y);
         ^~~~~
/in/foo.c:16:9: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
     e = abs(l / g);
         ^~~