/in/foo.cc: In function 'int main()':
/in/foo.cc:15:12: warning: statement has no effect [-Wunused-value]
     for (k1; k1<=k2; k1++)
            ^
/in/foo.cc:16:9: error: 'sum' was not declared in this scope
         sum=k2;
         ^~~
/in/foo.cc:17:6: error: 'sum' was not declared in this scope
      sum+=k1;
      ^~~