/in/foo.c:6:27: error: expected ';', ',' or ')' before '&' token
 int exgcd(int a,int b,int &x,int &y)
                           ^
/in/foo.c: In function 'main':
/in/foo.c:28:11: warning: implicit declaration of function 'exgcd' [-Wimplicit-function-declaration]
         d=exgcd(a,b,x,y);
           ^~~~~