struct should be declared extern

[abe-101]

When the struct is initialized in the header file each time the file gets included it gets initialized result in the following errer

/usr/bin/ld: quicksort.o:(.bss+0x0): multiple definition of `inventory'; inventory.o:(.bss+0x0): first defined here
collect2: error: ld returned 1 exit status
make: *** [Makefile:5: inventory] Error 1

the solution is to use extern and only initialize it once in inventory.c.