/in/foo.c: In function 'main':
/in/foo.c:5:17: error: expected identifier or '(' before 'long'
  int a[10000],n,long x,y,i;
                 ^~~~
/in/foo.c:7:6: error: 'i' undeclared (first use in this function)
  for(i=0;i<n;i++)
      ^
/in/foo.c:7:6: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:9:2: error: 'x' undeclared (first use in this function)
  x=a[0];
  ^
/in/foo.c:12:3: error: 'y' undeclared (first use in this function)
   y=a[i+1];
   ^
/in/foo.c: In function 'gcd':
/in/foo.c:28:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^