Having Issues With C++ Project

I am having issues with a programming project.
I haven't coded in about a year but I have quite a bit of code and need help just putting it all together.

The objectives of this program are to take a line of text from the user and put it in a string.
The string is then passed through two filters. The first removes all words that are three letters.
The second removes all words that have a the letter q in them and replace the whole word with the letter x

Any help would be very much appreciated.

#include <iostream>
#include <cstdlib>
#include <string>

using namespace std;

void threeletter(string s);
void qkiller();

int main()
{   string s;
    cout << "Enter a line of text followed by the enter key" << endl;
    getline(cin, s);
    threeletter(s);


}

void threeletter(string s,)
{
    int index, index2;

    index=s.find(' ');
    index2=s.rfind(' ', index-1);
    if ((index==string::npos)&&(index2==string::npos))
        s=" ";
    if (index==string::npos)

    if (index2==string::npos)

    if (index2-index== 4)
        s.erase(index, 4);
}
  
void qkiller()
{
    string s;
    int first,last,number ,place;
    place=s.find('q');
    first=s.rfind(' ', place-1);
    last=s.find(' ', place+1);
    if ((first==string::npos)&&(last==string::npos))
        s="x";
    if (first==string::npos)

    if (last==string::npos)

    number=last-first;

}