/in/foo.c: In function 'main':
/in/foo.c:8:22: warning: statement with no effect [-Wunused-value]
   for (i = 1; i++; i <= n)
                    ~~^~~~
/in/foo.c:10:15: warning: implicit declaration of function 'pow' [-Wimplicit-function-declaration]
  sum = sum + (pow(10, i) - 1) / 9;
               ^~~
/in/foo.c:10:15: warning: incompatible implicit declaration of built-in function 'pow'
/in/foo.c:10:15: note: include '<math.h>' or provide a declaration of 'pow'
/in/foo.c:8:16: warning: iteration 2147483646 invokes undefined behavior [-Waggressive-loop-optimizations]
   for (i = 1; i++; i <= n)
               ~^~
/in/foo.c:8:3: note: within this loop
   for (i = 1; i++; i <= n)
   ^~~