/in/foo.c: In function 'main':
/in/foo.c:5:10: error: redeclaration of 'num' with no linkage
  int num,num = 0;
          ^~~
/in/foo.c:5:6: note: previous declaration of 'num' was here
  int num,num = 0;
      ^~~
/in/foo.c:12:11: error: 'o' undeclared (first use in this function)
   int z = o;
           ^
/in/foo.c:12:11: note: each undeclared identifier is reported only once for each function it appears in