foo.cc: In function 'int main()':
foo.cc:18:14: warning: statement has no effect [-Wunused-value]
   18 |         for (i; i<=n; i++)
      |              ^
foo.cc:34:13: warning: statement has no effect [-Wunused-value]
   34 |         for(k;k<i-1;k++)
      |             ^
foo.cc:44:13: warning: statement has no effect [-Wunused-value]
   44 |         for(j;j<=n;j++)
      |             ^