[C++] ช่วยแก้โค๊ดเปรียบเทียบค่าจัดเก็บหน่อยครับ

if (unit != "cm"&& unit != "m" &&unit != "in"&&unit != "ft")
            cout << "The unit given is not accepted\n"
                << "Enter a length value with a unit\n";
        //__________illegal unit indicator___________________________________________
        else if (unit == "cm")
        {
                            cout << length << " cm is " << 0.01*length << " m\n"; //เปลี่ยน cm เป็น m
                             meter = 0.01*length; //เก็บค่าเป็นความยาว
                             sum += (0.01*length); //บวกความยาวตามลูป
                            cout << "The sum of length is " << sum << " m\n"; //แสดงผลบวก
        }
        //______________cm____________________________________________________________________
        else if (unit == "in")
        {
            cout << length << " in is " << 0.0254*length << " m\n"; //เปลี่ยน in เป็น m
            meter = 0.0254*length;
            sum += (0.0254*length);
            cout << "The sum of length is " << sum << " m\n";
        }
        //________________in____________________________________________________
        else if (unit == "ft")
        {
            cout << length << " ft is " << 0.3048*length << " m\n"; //เปลี่ยน ft เป็น m
            meter=0.3048*length;
            sum += (0.3048*length);
            cout << "The sum of length is " << sum << " m\n";
        }
        //_____________________________ft___________________________________________
        else if (unit == "m")
        {
        cout << length << " m is " << length << " m\n"; //เมตรเหมือนเดิม
        meter=length;
        sum += length;
        cout << "The sum of length is " << sum << " m\n";
        }
        if (meter<shortest)
        {
            shortest = meter;
        }
        else if (meter>longest)
        {
            longest = meter;
        }
        cout << shortest << " m is the shortest so far\n"
            << longest << " m is the longest so far\n";
        cin >> next >> unit;
        }while (length=next);