Line 21: Char 40: error: reference to non-static member function must be called 21 | sort(words.begin(),words.end(),lencom); | ^~~~~~1 error generated.

The error message you're seeing is because you're trying to use a non-static member function as a comparison function for std::sort. The comparison function should be either a standalone function or a static member function.

Here's how you can fix it:

1. If lencom is a method of a class, you should make it a static method. Here's an example:

class MyClass {
public:
    static bool lencom(const string &a, const string &b) {
        return a.length() < b.length();
    }
};

Then you can call it like this:

sort(words.begin(), words.end(), MyClass::lencom);

2. If lencom doesn't need to access any member variables, you can make it a standalone function:

bool lencom(const string &a, const string &b) {
    return a.length() < b.length();
}

Then you can call it like this:

sort(words.begin(), words.end(), lencom);

3. If lencom needs to access member variables, you can use a lambda function to capture the necessary variables:

auto lencom = [this](const string &a, const string &b) {
    return a.length() < b.length();
};
sort(words.begin(), words.end(), lencom);

Remember to include the necessary headers and use the correct namespaces as needed.