cannot convert from "void" to "std::basic_string"

[vaderboi]

I am writing a Bull Cow Game program and am getting a weird error in my header file.

The error is: "'initializing': cannot convert from 'void' to 'std::basic_string<char,std::char_traits<char>, std::allocator<char>>" is on line 9 and 10 of BullCowGame.cpp. What does this mean?

I am compiling using the Visual Studio 2017 compiler.

main.cpp

#include <iostream>
#include <string>
#include "BullCowGame.h"

using namespace std;

void printIntro();
string getGuess();
void playGame();

int main()
{
	printIntro();

	playGame();
	
	return 0;
}


void printIntro()
{
	constexpr int WORD_LENGTH = 5;

	cout << "Welcome to Bulls and Cows, a fun word game.\n" << endl;
	cout << "Can you guess the " << WORD_LENGTH << " letter isogram I am thinking of?\n" << endl;
}

void playGame()
{
	constexpr int NUM_OF_TURNS = 10;
	string answer = "barn";

	for (int i = 0; i < NUM_OF_TURNS; i++)
	{
		BullCowGame bullCowGame;

		string guess = getGuess(); 

		bullCowGame.setNumOfCows(guess, answer);
		bullCowGame.setNumOfBulls(guess, answer);

		cout << "Number of Bulls: " << bullCowGame.getNumOfBulls()
 << "  Number of Cows: " << bullCowGame.getNumOfCows() << endl;
		cout << endl;

	}

}

string getGuess()
{
	string guess = "";

	cout << "Enter your guess: ";

	getline(cin, guess);
	cout << endl;

	return guess; 
}

BullCowGame.h

#ifndef BULL_COW_GAME_H
#define BULL_COW_GAME_H

#include <string>

using namespace std; 

class BullCowGame
{
public:
	explicit BullCowGame(int initialBull = 0, int initialCow = 0)
		:storedBulls{ initialBull }, storedCows{ initialCow } {}
	
	void setNumOfCows(string guess, string answer);
	int getNumOfCows();
	void setNumOfBulls(string guess, string answer);
	int getNumOfBulls();

		
private:
	int storedBulls = 0;
	int storedCows = 0;
	
	
};

#endif	 

BullCowGame.cpp

#include <string>
#include <algorithm>
#include "BullCowGame.h"

using namespace std;

void setNumOfCows(string guess, string answer)
{
	string sortedGuess = sort(guess.begin(), guess.end());
	string sortedAnswer = sort(answer.begin(), answer.end());

	for (unsigned int i = 0; i < answer.size(); i++)
	{
		/*in order for the character at the current index of the Guess to be a Cow
		it must be BOTH a character found somewhere in the Answer
		AND NOT identical to the character at the same index of Answer
		(i.e. if guess == "Marf" and answer == "Farm", "M" and "F" in the Guess
		would be Cows since they are characters found in answer but are in the wrong
		place; "A" and "R" would NOT be Cows even though they are characters found in
		the Answer because they ALSO are identical characters at the same respective
		index locations in Answer)*/
		if ((guess[i] != answer[i]) && (sortedGuess[i] == sortedAnswer[i])
		{
			storedCows++;
		}
	}

}

int getNumOfCows()
{
	return storedCows;
}

void setNumOfBulls(string guess, string answer)
{
	for (unsigned int i = 0; i < answer.size(); i++)
	{
		if (guess[i] == answer[i])
		{
			storedBulls++;
		}
	}
}

int getNumOfBulls()
{
	return storedBulls;
}

[salem c]

> The error is: "'initializing': cannot convert from 'void' to 'std::basic_string<char,std::char_traits<char>, std::allocator<char>>" is on line 9 and 10 of BullCowGame.cpp. What does this mean?

It means sort() returns void.
http://www.cplusplus.com/reference/algorithm/sort/

Sort sorts the thing 'in place'.

[vaderboi]

What thing 'in place'? The guess variable? Or something else?

[vaderboi]

So it seems like you can't assign the sorted string to a variable?

I changed lines 9 and 10 to this:

string sortedGuess = guess;
sort(sortedGuess.begin(), sortedGuess.end());
	
string sortedAnswer = answer;
sort(sortedAnswer.begin(), sortedAnswer.end());

and the compiler didn't throw an error.

I guess my question is: What doesn't sort() returning void mean? How can you return "void"?

[Peter87]

The error is: "'initializing': cannot convert from 'void' to 'std::basic_string<char,std::char_traits<char>, std::allocator<char>>" is on line 9 and 10 of BullCowGame.cpp. What does this mean?

std::string is actually a typedef for std::basic_string<char, std::allocator<char>> so what the error actually says is that it cannot convert from void to std::string.

So it seems like you can't assign the sorted string to a variable?

std::sort manipulates the sequence in-place. It does not produce a new string. After you have called sort(guess.begin(), guess.end()) the guess string will now be sorted.

I guess my question is: What doesn't sort() returning void mean? How can you return "void"?

What he means is that the return type is void, which means the function does not return any values.