How do I share a global variable between c files?

If I define a global variable in a .c file, how can I use the same variable in another .c file?

file1.c:

#include<stdio.h>

int i=10;

int main()
{
    printf("%d",i);
    return 0;
}

file2.c:

#include<stdio.h>

int main()
{
    //some data regarding i
    printf("%d",i);
    return 0;
}

How can the second file file2.c use the value of i from the first file file1.c?