Problem with rand()

Hello folks I am having a really odd problem with the random number generator. For example when I set the max range to 6, I am getting some results that are 7.

Here is the class implementation where the function for rolling the dice is located. Pretty simple stuff

  // Constructor
Die::Die()
{
	sides = 0;
}
Die::Die(int dieSides)
{
	sides = dieSides;
}
// Roll Function
int Die::roll()
{
	return rand()& sides + 1;
}

In another file, for my Game class I have Die included as one of its member variables, such as

class WarGame
{
	private:
		int rounds;
		int type1, type2;
		string player1;
		string player2;
		int* player1Scores;
		int* player2Scores;
		Die* dice;
                
                // This is the function for assigning the sides
                void setSides(int);


// Here I am setting the sides
void WarGame::setSides(int sideTotal)
{
	dice = new Die(sideTotal);
}


// Here I am calling the dice object to provide a score to the player
// Like mentioned before if I set the total sides to 4, some scores end up being 5.
void WarGame::simulateGame()
{
	for (int x = 0; x < rounds; x++)
	{
		if (type1 == 1)
		{
			player1Scores[x] = dice->roll();
		}
		else if (type1 == 2)
		{
			player1Scores[x] = dice2->rollLoaded(); // ignore this
		}
	}
}

Here is the output showcasing the error. As you can see in round 4 player 1 got a 7, even though the number of sides is set to 6


What is the number of sides each player will use? 6
What type of dice will player 1 use?
1. Regular Dice
2. Loaded Dice
1

What type of dice will player 2 use?
1. Regular Dice
2. Loaded Dice
1

How many rounds do you want the players to play? 4
Round 1
Player 1: 2
Player 2: 5

Round 2
Player 1: 0
Player 2: 6

Round 3
Player 1: 2
Player 2: 4

Round 4
Player 1: 7
Player 2: 1

Player 2 has won the game, congratulations

I never had this issue before working with random numbers, if anyone can point out why I this is happening it would be highly appreciated. Thanks

Last edited on

cire (8284)

int Die::roll()
{
	return rand()% sides + 1;
}

The bitwise AND operator (&) is not a replacement for the modulus operator (%).

gutty333 (22)

OMG no way wow, How was I not able to find that. I blame my IDE for not pointing it out LOL. In all seriousness though thanks a lot cire. Even though is irrelevant, curious to know what operation the & was doing there.

Moschops (7244)

I appreciate you're just learning and playing, but I'd be remiss if I did not point you at this excellent talk about random values in C++, by Stephan T. Lavavej - he's a face on the C++ scene.

https://channel9.msdn.com/Events/GoingNative/2013/rand-Considered-Harmful

gutty333 (22)

thank you will most definitely take a look

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