Which is better function() return; or function(reference)

[giblit]

Which method is better to use? return or reference or is it just a preference thing.

  #include <iostream>
#include <stdlib.h>
using namespace std;
unsigned int returnfunction(unsigned int);
void referencefunction(unsigned int&);
int main()
{	
	unsigned int number;
	string option, numberstr, error;
	do {
		cout << "Would you like to use return method or reference(1 or 2)?" << flush;
		getline(cin, option);
	} while(option.size() > 1 || option.size() < 1 || (option[0] != '1' && option[0] != '2'));
	do {
		cout << "Please enter a number: " << flush;
		getline(cin, numberstr);
		for(unsigned int i = 0; i < numberstr.size(); i++) if(isalpha(numberstr[i])) error = "true"; else error = "false";
	} while(error == "true");
	number = atoi(numberstr.c_str());
	switch(option[0]){
		case '1': number = returnfunction(number); cout << "Returned: " << number << endl; break;
		case '2': referencefunction(number); cout << "Reference: " << number << endl; break;
	}
}

unsigned int returnfunction(unsigned int a)
{
	unsigned int b = ++a;
	return(b);
}

void referencefunction(unsigned int &a)
{
	a++;
}

[Disch]

Returning a value offers more flexibility in usage, often times making it more simplistic to use... and therefore should be preferred.

Especially if you don't want the passed variable to be modified.

[giblit]

Alright thanks and can you return multiple values? because If you are modifying mulitple variables it is easy using references eg:

 void function(unsigned int&, unsigned int&);
int main()
{
unsigned int num1 = 0, num2 = 0;
cout << "Before: " << endl;
cout << "num1: " << num1 << endl;
cout << "num2: " << num2 << endl;
function(num1, num2);
cout << "After: " << endl;
cout << "num1: " << num1 << endl;
cout << "num2: " << num2 << endl;
}
void function(unsigned int &a, unsigned int &b)
{
a++;
b++; b++;
}

[Disch]

can you return multiple values?

No. The closest you can do to that is return a class/struct instance which contains multiple values.... but that's often less convenient than passing by reference.


Though the need to output multiple values isn't as common as you might be thinking.

[giblit]

Yeah I can't think of too many scenario's I was just wondering because I was making a simple "final project" for my class at school and I needed to return 2 values one for if the guess was too high, and one for if the guess was too low. here's what I did:

#include <iostream>
#include <stdlib.h>
void mainmenu(std::string);
void start(std::string);
void check(std::string&);
unsigned int convert(std::string);
unsigned int rand(unsigned int, unsigned int);
void guessed(std::string, unsigned int, char&, unsigned int&, unsigned int&);
void quit(std::string);

int main()
{
	std::string name;
	do {
		std::cout << "What is your name? " << std::flush;
		std::getline(std::cin,name);
		for(unsigned int i = 0; i<name.size(); i++) if(!isalpha(name[i])) name = "false";
		if(name == "false") std::cout << "Invalid name.\n" << std::flush;
	} while(name == "false");
	std::cout << "I'm glad you could play my game " << name << '\n' << std::flush;
	mainmenu(name);
	return(0);
}

void mainmenu(std::string a)
{
	std::string input;
	do {
		std::cout << a << " please enter \"P\" to play.\n" << a << " please enter \"Q\" to quit.\nChoice: " << std::flush;
		std::getline(std::cin,input);
		for(unsigned int i = 0; i<input.size(); i++) input[i] = toupper(input[i]);
		if(input != "P" && input != "Q") std::cout << "Invalid choice " << a << ".\n" << std::flush;
	} while(input != "P" && input != "Q");
	switch(input[0]){
		case 'P': start(a); break;
		case 'Q': quit(a); break;
	}
}

void start(std::string a)
{
	std::string low, high, guess;
	unsigned int l, h, r, i = 0;
	char g;
	do {
		std::cout << a << " what range would you like?(ex. 1-100)...\nLowest Value: " << std::flush;
		std::getline(std::cin,low);
		std::cout << "Highest Value: " << std::flush;
		std::getline(std::cin,high);
		check(low);
		check(high);
		l = convert(low);
		h =convert(high);
		if(low == "false" || high == "false" || l >= h) std::cout << "Invalid range " << a << ".\n" << std::flush;
	} while(low == "false" || high == "false" || l >= h);
	
	r = rand(l, h);
	
	do {
		i++;
		std::cout << a <<" please guess a number between " << l << " and " << h << "\nGuess " << i << ": " << std::flush;
		std::getline(std::cin,guess);
		check(guess);
		if(guess != "false") guessed(guess, r, g, l, h);
	    else std::cout << "Invalid guess " << a << '\n' << std::flush;
	} while (g != 't');
	if(i != 1) std::cout << "\nGreat job " << a << "!\nIt only took you " << i << " tries to guess the random number \"" << r << "\".\n\n" << std::flush;
	else std::cout << "\nGreat job " << a << "!\nIt only took you " << i << " try to guess the random number\"" << r << "\".\n\n" << std::flush;
	mainmenu(a);
}

void check(std::string &a)
{
	for(unsigned int i = 0; i<a.size(); i++) if(!isdigit(a[i])) a = "false";
}

unsigned int convert(std::string a)
{
	unsigned int b;
	b = atoi(a.c_str());
	return(b);
}

unsigned int rand(unsigned int a, unsigned int b)
{
	unsigned int c;
	srand(time(0));
	c = rand() % (b - a + 1) + a;
	return(c);
}

void guessed(std::string a, unsigned int b, char &c, unsigned int &d, unsigned int &e)
{
	unsigned int guess;
	guess = convert(a);
	if(guess < d || guess > e) std::cout << "Invalid guess.\n" << std::flush;
	if(guess > b && guess < e){ std::cout << "You guessed too high.\n" << std::flush; e = guess - 1; }
	if(guess < b && guess > d){ std::cout << "You guessed too low.\n" << std::flush; d = guess + 1; }
	if(guess == b) c = 't';
}

void quit(std::string a)
{
	std::cout << "Good bye " << a << ".\nPlease play again!" << std::flush;
}

and I did the std:: because I figure it will compile slightly faster than if you do the using namespace std since I figured that would include all the unnecessary std's eg std::vector but the program is very small so it probably would be unnoticable.

one more question though disch when would you EVER use a static number I did an experiment with them with this code:

#include <iostream>
using namespace std;

void staticintfunc(void);
void autointfunc(void);

int main(void)
{
	for(unsigned int i = 0; i<5; i++) staticintfunc();
	for(unsigned int i = 0; i<5; i++) autointfunc();
}

void staticintfunc(void)
{
	static int a = 0;
	a++;
	cout << "Static: " << a << endl;
}

void autointfunc(void)
{
	unsigned int a = 0;
	a++;
	cout << "Auto: " << a << endl;
}