Header files and libraries (Kevin Lynch)

For more information, see http://nu32.org.  This video is a supplement to the book "Embedded Computing and Mechatronics with the PIC32 Microcontroller," Lynch, Marchuk, and Elwin.  It is part of Northwestern University's ME 333 Introduction to Mechatronics.

L-comp:  Say you have a header file header.h, and inside it it has the statement

float HelperFloat;

Then this header is included by both file1.c and file2.c.  These compile successfully to file1.o and file2.o.  When these two codes are linked into a single executable, though, the linker fails.  Explain why.