/in/foo.c: In function 'main':
/in/foo.c:23:6: error: conflicting types for 'a'
  int a[600];
      ^
/in/foo.c:22:6: note: previous declaration of 'a' was here
  int a,b,c;
      ^
/in/foo.c:29:2: error: 'nc' undeclared (first use in this function)
  nc=Merge(a,na, b,nb, c);
  ^~
/in/foo.c:29:2: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:29:13: error: 'na' undeclared (first use in this function)
  nc=Merge(a,na, b,nb, c);
             ^~
/in/foo.c:29:19: error: 'nb' undeclared (first use in this function)
  nc=Merge(a,na, b,nb, c);
                   ^~
/in/foo.c:29:17: warning: passing argument 3 of 'Merge' makes pointer from integer without a cast [-Wint-conversion]
  nc=Merge(a,na, b,nb, c);
                 ^
/in/foo.c:3:5: note: expected 'int *' but argument is of type 'int'
 int Merge(int a[],int na, int b[],int nb, int c[])
     ^~~~~
/in/foo.c:29:23: warning: passing argument 5 of 'Merge' makes pointer from integer without a cast [-Wint-conversion]
  nc=Merge(a,na, b,nb, c);
                       ^
/in/foo.c:3:5: note: expected 'int *' but argument is of type 'int'
 int Merge(int a[],int na, int b[],int nb, int c[])
     ^~~~~