Answer SL23

99 

Comments: There is just one object x, which is referred to in all three files.

When the executable program is loaded into memory, there is just one x, which holds an 8.

The main() function starts running and calls foo() which changes x to 99. x continues to hold 99 when control returns to main() .

Contrast this to the previous two puzzles where the x in foo() is a local variable with no linkage.

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/* --- fileA.c --- */
int x = 8;

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/* --- fileB.c --- */
void foo()
{
  extern int x;
  x = 99;
}

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/* --- fileC.c --- */
#include <stdio.h>
void foo();

extern int x;
void main()
{
  foo();
  printf("%d\n", x );
}

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