在字符串向量中对大小写单词进行排序

Question

I'm trying to alphabetize words in a vector of strings and my program is distinguishing between upper and lowercase letters, so uppercase words always appear first in the sorted list. I can think of potentially really cumbersome ways to make sure the upper case words go in their place, but is there a simple way to do this?

Here is my code:

for (int i = 0; i < str.size(); i++)
    {
        for (int j = 0; j < str.size(); j++) 
        {
            if (str.at(i) > str.at(j))
            {               
                temp = str.at(j);
                str.at(j) = str.at(i);
                str.at(i) = temp;
            }   
        }
    }

Also, this is for a programming assignment, so I am not allowed to use built in C++ functions to do this and I have to use a vector.

Answer 1

The trick to solving this is to write a replacement for this line

if (str.at(i) > str.at(j))

that performs case-insensitive comparison. Start by writing a signature for it:

bool greaterThanIgnoreCase(const string& left, const string& right) {
    ...
}

Now you can replace your if condition with a call to this new function:

if (greaterThanIgnoreCase(str.at(i), str.at(j)))

Finally, you need to provide an implementation of greaterThanIgnoreCase function. This is the core of the problem, so you would need to do it yourself. The trick to it is using toupper or tolower function on each character of strings left and right , and compare them one character at a time. If you run out of characters in one of the strings, the one with some characters remaining should be considered greater.

Answer 2

If you have a vector of string s then you could/should use the STL library, which offers sort or stable_sort for a given comparison function (that can be a simple lambda expression, functor, function,...).

Update: You're not allowed to use built-in types except vector. In this case you can develop easily a replicate of what STL does.

Define a sort function that receives a comparator (for a vector of strings).

Answer 3

The only thing you need to do is to compare lowercased characters. If you are not allowed to use any built-in functions, you can do it manually.

Since lowercase characters are located in ASCII table starting from 97, and uppercase - starting from 65, you can simply add 32 to the uppercase char to get its lowercase equivalent.

char lowerCase(char c)
{
    if (c >= 'A' && c <= 'Z') // if char is uppercase
        return (char)(c + 32); // return its lowercase equivalent
    else
        return c;
}

Then, you can do the following in your if condition:

if (lowerCase(str.at(i)) > lowerCase(str.at(j)))

Note that you shouldn use lowerCase only when you compare, but not when you assign.

Here is the working IDEOne demo .