/in/foo.cc: In function 'int main()':
/in/foo.cc:33:28: error: 'o' was not declared in this scope
         for(int j=sum;j>=a[o];j--)
                            ^
/in/foo.cc:34:15: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
             if(f[j-a[i]]>0)
               ^