/in/foo.cc: In function 'int main()':
/in/foo.cc:12:9: error: 'c' was not declared in this scope
  system(c);
         ^
/in/foo.cc:10:15: warning: unused variable 'i' [-Wunused-variable]
  register int i,j;
               ^
/in/foo.cc:10:17: warning: unused variable 'j' [-Wunused-variable]
  register int i,j;
                 ^