/in/foo.cc: In function 'int main()':
/in/foo.cc:11:8: warning: statement has no effect [-Wunused-value]
  for (i; i < n; i++)
        ^
/in/foo.cc:14:8: warning: statement has no effect [-Wunused-value]
  for (j; j < q; j++)
        ^
/in/foo.cc:19:9: warning: statement has no effect [-Wunused-value]
   for (k; k < v; k++)
         ^
/in/foo.cc:20:13: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
    if (a[k] = 0)
        ~~~~~^~~