need to code the function definitions

[Jhub]

I am writing a hangman game code and I am having trouble defining, implement and correctly invoking these 3 functions exactly as declared below.

@brief Puts dashes in place of alphabetic characters in the phrase.
@param phrase the phrase to be solved
@return the phrase with all alphabetic characters converted to dashes

string setupUnsolved(string phrase);

@brief Replaces the dashes with the guessed character.
@param phrase the phrase to be solved
@param unsolved the phrase with dashes for all unsolved characters
@param guess the char containing the current guessed character
@return the new unsolved string with dashes replaced by new guess

string updateUnsolved(string phrase, string unsolved, char guess);

@brief Gets valid guess as input.
A guess is taken as input as a character. It is valid if
1) it is an alphabetic character; and
2) the character has not already been guessed
@param prevGuesses the string containing all characters guessed so far
@return a valid guess and only a valid guess as a character

char getGuess(string prevGuesses);

Here is what I have any suggestions or hints would be wonderful!

#include <iostream>
#include <iomanip>
#include <string>
#include "assn4.h"
using namespace std;

string setupUnsolvedPhrase(string);
string updateUnsolvedPhrase(string, string, char);

int main()
{  
    int wrongGuess = 0;
    int guessesLeft = 7 - wrongGuess;
    string phrase, prevGuesses;
    char guess, validGuess;
    
    
    cout << "Enter phrase: ";
    getline(cin, phrase);
    
    
    
    clearScreen();
     
    string unsolved = setupUnsolvedPhrase(phrase);
    cout << "Phrase : " << unsolved << endl;
    cout << "Enter a guess: ";
    cin >> guess;
    unsolved = updateUnsolvedPhrase(phrase, unsolved, guess);
    cout << endl;
    
    while (phrase!=unsolved)
    { 
          
         cout << "Phrase : " << unsolved << endl << endl;
         cout << "Guessed so far: " << prevGuesses << endl;
         cout << "Wrong guesses left: " << guessesLeft << endl << endl;
         cout << "Enter a guess: ";
         cin >> guess;
         //getNewGuess(prevGuesses);
         prevGuesses += guess;
         cout << "Previous guesses: " << prevGuesses << endl;
         unsolved = updateUnsolvedPhrase(phrase, unsolved, guess);           
    }
    cout << "Congratulations!!" << endl;
    
    
}


string setupUnsolvedPhrase(string phrs){
    //I think I need the definition here
    return "";
}

string updateUnsolvedPhrase(string phrs, string unslvd, char g)
{
  
    return "";
}