foo.cc: In function 'int main()':
foo.cc:4:8: warning: unused variable 'n' [-Wunused-variable]
  int x,n,m,a;
        ^
foo.cc:4:10: warning: unused variable 'm' [-Wunused-variable]
  int x,n,m,a;
          ^
foo.cc:4:12: warning: variable 'a' set but not used [-Wunused-but-set-variable]
  int x,n,m,a;
            ^