//  playExternCaller.c
 //
 //
 //  Created by Ying Li on 2/23/20.
 //
 // This is the main program
 // 
 // Compile:
 // gcc -o playExternCaller playExternCaller.c playExtern.c
 //
 // Illustrates that the proper way to make a truly global variable
 // is to use the extern keyword. 
 // declare it with the extern keywork in the header file of the file that gets to 
 // claim some sort of ownership over the variable.
 // then define it (i.e. give it a value) in the .c file
 // then other files that want to use it include the .h file and can use it, with ]
 // all files referring to the same variable in the same location of memory.

// # means "pre-processing command"
// #include means "copy-paste playExtern.h into this file before compiling it"
#include "playExtern.h"

// extern int glbA; // redundant if in playExtern.h
// int gblA; // not appropriate way
// We do not need to declare gblA because we included playExtern.h

int main () {
    printf("main: Caller gblA %d at Address %p\n", gblA, &gblA);
    printExternVal();
    printf("main: Caller gblA %d at Address %p\n", gblA, &gblA);
    gblA = 10;
    printf("main: Caller gblA %d at Address %p\n", gblA, &gblA);
    printExternVal();
    return 0;
}