Global Variable

global.cpp

// declaration of g_nValue


int g_nValue = 5;

global.h

#ifndef GLOBAL_H // header guards
#define GLOBAL_H
 
// extern tells the compiler this variable is declared elsewhere
extern int g_nValue;
 
#endif

main.cpp

#include "global.h"
int main()
{
    g_nValue = 7;
    return 0;
}