declaration - declare extern variable within a C function? -

i define variable in c file: int x, , know should use extern int x declare in other files if want use in other files.

my question is: should declare in other files?

1. outside of functions,

   // in file a.c: int x;  // in file b.c: extern int x; void foo() { printf("%d\n", x); } 

2. within function(s) use it?

   // in file b.c: void foo() {    extern int x;    printf("%d\n", x); } 

my doubts are:

• which 1 correct?, or
• which preferred if both correct?

1. both correct.

2. which 1 preferred depend on scope of variable's use.

   • if use in 1 function, declare in function.

     void foo()  {      extern int x;   <--only used in function.      printf("%d",x);    } 

   • if used more 1 function in file, declare global value.

     extern int x;   <-- used in more 1 function in file void foo() {     printf("in func1 :%d",x);    }     void foo1()  {     printf("in func2 :%d",x);    }