[user02@FC4 Lesson13]$ cat -n global.c

   1  #include <stdio.h>
   2
   3  int number = 1001;
   4
   5  void first_change(void)
   6  {
   7     printf("number's value in first_change %d\n", number);

   8     ++number;
   9  }
  10
  11  void second_change(void)
  12  {
  13     printf("number's value in second_change %d\n", number);
  14     ++number;
  15  }
  16
  17  int main(void)
  18  {
  19     printf("number's value in main %d\n", number);
  20     ++number;
  21     first_change();
  22     second_change();
  23
  24     return 0;
  25  }

[user02@FC4 Lesson13]$ gcc -std=c99 -o global global.c
[user02@FC4 Lesson13]$ ./global
number's value in main 1001
number's value in first_change 1002
number's value in second_change 1003
[user02@FC4 Lesson13]$