Function to alter a variable value and then return to the function?

[Elarionus]

So for a project, I'm creating an adventure game. One of the requirements is at the start of every room, it needs to display how much oxygen is left. I was initially going to do it with a game wide variable that would set itself at the beginning of every function, with oxygen = oxygen - 5, but the oxygen needs to be in a separate function, as per the requirements. I don't really understand how to move back and forth between functions very well, especially ones that are supposed to print a value at the start of every single room.

Here is my code so far.

  /*
* February 17, 2018
* Assignment 04
* Section 02
*/

#include <iostream>
#include <stdlib.h> //This is the library for seeding the srand()
using namespace std;

//Function Prototypes
int menu();
//int oxygen();
int room1();
int room2();
int room3();
int room4();
int room5();
int room6();
int gameover();
int gamewin();

//Game-Wide Variables
int oxygen = 120;


//Main Function
int main()
{
	menu();
}

//Menu for play or exit
int menu()
{
	int menuchoice;
	cout << "Welcome to Asylum! Would you like to play?\n1 - Play\n2 - Exit\n";
	cin >> menuchoice;

	switch (menuchoice)
	{
	case 1: 
		room1();
		break;
	case 2: 
		return 0;
		break;
	default:
		cout << "Invalid Choice.\n\n";
		menu();
	}
}

//Oxygen Function
/*int oxygen()
{

}
*/

//Functions for rooms. The various text passages are separated into multiple cout statements so that it is easier to read for the programmer.

//Function Room 1
int room1()
{
	int room1choice;

	cout << "\n********** Oxygen Remaining: " << oxygen << " **********\n";
	cout << "Welcome to the Asylum.\n";
	cout << "You see a door on your right and a door on your left.\n";
	cout << "The door on your left has a cool breeze blowing from it. The door on your right smells of musty water.\n\n";
	cout << "Which door would you like to go through?\n";
	cout << "1 - Right\n2 - Left\n";
	cin >> room1choice;

	switch (room1choice)
	{
	case 1: room2();
		break;
	case 2: room3();
		break;
	default:
		cout << "Inavlid Choice.\n\n";
		room1();
	}



	return 0;
}

//Function Room 2
int room2()
{
	int room2choice;
	oxygen = oxygen - 5;
	cout << "\n********** Oxygen Remaining: " << oxygen << " **********\n";
	cout << "You hear a strange voice calling to you...in the corner, there is a box with a red box, yellow triangle, and blue square on it.\n";
	cout << "Which one do you press?\n";
	cout << "1 - Red Box\n2 - Yellow Triangle\n3 - Blue Square\n";
	cin >> room2choice;

	switch (room2choice)
	{
	case 1: 
		cout << "\nA hidden door opens in the wall, revealing a new path.\n";
		room3();
		break;
	case 2: 
		cout << "\nA hole in the ceiling opens above you, and a large bucket of acid comes pouring down on your head, killing you instantly.\n";
		gameover();
		break;
	case 3:
		cout << "\nA trap door opens beneath you, and you are surprised to find yourself back where you began!\n\n";
		room1();
		break;
	default:
		cout << "Inavlid Choice.\n\n";
		room2();
	}

	return 0;
}

//Function Room 3
int room3()
{
	int room3choice;
	cout << "\nThere is a blood spattered hospital bed in the corner of a room. Next to it is a partially open closet door.\n";
	cout << "Do you approach the bed, open the closet, or leave through the next door?\n";
	cout << "1 - Approach the Bed\n2 - Open the Closet\n3 - Leave\n";
	cin >> room3choice;

	switch (room3choice)
	{
	case 1:
		cout << "\nA horrendous monster is crouched behind the bed. It slowly stands up and grabs you, tearing you apart, as your screams echo throughout the chambers.";
		gameover();
		break;
	case 2:
		cout << "You open the closet door and step through it...\n\n";
		room5();
		break;
	case 3:
		room4();
		break;
	default:
		cout << "Inavlid Choice.\n\n";
		room3();
	}

	return 0;
}

//Function Room 4
int room4()
{
	int room4choice;
	cout << "You find yourself in a large courtyard area, with an old, rusty basketball court. You see a ball on the ground.\n";
	cout << "Do you go for the slam dunk, the three pointer, or the half court shot?\n";
	cout << "1 - Slam Dunk\n2 - Three Pointer\n3 - Half Court\n";
	cin >> room4choice;

	switch (room4choice)
	{
	case 1:
		cout << "\nYou soar towards the hoop, flying ever so gracefully, with not a care in the world!\n";
		cout << "The ball slams through the rim, through the hoop, as you come crashing in, grabbing the rim.\n";
		cout << "Out of nowhere, hundreds of NBA recruiters are all over you, desparately wanting you to play for them.\n";
		cout << "They take you out of the Asylum, and fly you away.\n";
		gamewin();
		break;
	case 2:
		cout << "\nYou shoot from the three point line, but miss horribly. You feel bad about yourself, and leave.";
		room5();
		break;
	case 3:
		cout << "\nWhat are you, a middle schooler? That's not cool anymore.\n";
		cout << "The ball flies into the rim, bounces back, and hits you in the head, killing you instantly.\n";
		gameover();
		break;
	default:
		cout << "Invalid Choice\n\n";
		room4();
	}
	return 0;
}

//Function Room 5
int room5()
{
	int room5choice;
	cout << "\nYou are now in an existential crisis. There's a computer in front of you with the Asylum game. Do you play it?\n";
	cout << "1 - Play\n2 - Leave\n";
	cin >> room5choice;

	switch (room5choice)
	{
	case 1:
		room1();
		break;
	case 2:
		room3();
	default:
		cout << "Inavlid Choice\n\n";
		room5();
	}
	return 0;
}

//Function Room 6
int room6()
{
	int room6choice;
	cout << "You're outside now, by a large gate. It has spikes on the top, and it is locked tight.\n";
	cout << "You notice a rocket launcher nearby. Do you shoot the rocket launcher at the gate, attempt to jump it, or head to the courtyard?\n";
	cout << "1 - Shoot the rocket launcher\n2 - Jump the gate\n3 - Head to the courtyard\n";
	cin >> room6choice;

	switch (room6choice)
	{
	case 1:
		cout << "You pull the trigger, but the launcher malfunctions, exploding and killing you instantly.\n";
		gameover();
		break;
	case 2:
		cout << "You attempt to jump over the gate, but you aren't as athletic as you thought. You are impaled and die instantly.\n";
		gameover();
		break;
	case 3:
		room4();
		break;
	default:
		cout << "Invalid Choice\n\n";
		room6();
	}
	return 0;
}

//Function Game Over
int gameover()
{
	int gameoverchoice;
	cout << "\nGame Over";
	cout << "\nWould you like to play again?";
	cout << "\n1 - Play Again\n2 - Exit\n";
	cin >> gameoverchoice;

	switch (gameoverchoice)
	{
	case 1: room1();
		break;
	case 2: 
		return 0;
		break;
	default:
		cout << "Invalid Choice\n\n";
		gameover();
	}

	return 0;
}

//Function Game Win
int gamewin()
{
	int gamewinchoice;
	cout << "Congratulations! You escaped!\n";
	cout << "\nWould you like to play again?";
	cout << "\n1 - Play Again\n2 - Exit\n";
	cin >> gamewinchoice;

	switch (gamewinchoice)
	{
	case 1: room1();
		break;
	case 2: 
		return 0;
		break;
	default:
		cout << "Invalid Choice\n\n";
		gamewin();
	}
}

[jonnin]

like this?

void foo(int &value)
{
value--;
}

...

cout << reavalue << endl;
foo(realvalue);
cout << reavalue << endl;

or, if I understood your explain correctly, this might be what you need:

int o2handler(int modify)
{
static int o2 = initial value;
o2 += modify; //you can add or subtract by using a negative value.
return o2;
}

cout << " current o2 is " << o2handler(0) << endl; //zero does nothing!


you can also do all the above in a class, or a singleton class, or other various approaches. This is the straightforward simple approach. It more or less is a heavily controlled global variable, but if you are careless with this technique you can still inherit some of the malfunctions those cause. You REALLY don't want to multi-thread something like that, for one example, esp for a more complex task.