Generation of random possible answers (multiple choice style)

[seph658]

char ans2;

    for(int i = 0; i < 10; i++)
    {

          cout << p2Q[i].getQuestion() << endl;

        for(int i = 0; i < 4; i++)
    {

        int randIndex = rand() %4; // generates a random number between 0 and 3
        cout << q1Possible[randIndex] << endl;
    }
        cin  >> ans2;

I'm not having any bugs, but this is more to see if there is something further I need to do in order to get my desired result.

My desired result is as follows:

Player 1:
     Who was the first President of the United States?
     1. Abe Lincoln
     2. LBJ
     3. George Washington
     4. Teddy Roosevelt

Player 2:
     Who was the first President of the United States?
     1. Teddy Roosevelt
     2. Abe Lincoln
     3. George Washington
     4. LBJ

Ok, so the aforementioned code works -too- perfectly. It generates my questions as expected and prints out the possible answers randomly. The problem is that sometimes the output is as follows:

Player 1:
     Who was the first President of the United States?
     1. Abe Lincoln
     2. Abe Lincoln
     3. George Washington
     4. Teddy Roosevelt

Player 2:
     Who was the first President of the United States?
     1. Teddy Roosevelt
     2. Teddy Roosevelt
     3. George Washington
     4. Teddy Roosevelt

Is there anything else I could be doing or maybe some other suggestion as to how to handle this situation?

[cppnoob25]

You could push your randIndex into a vector and check against those values in your vector until randIndex returns a value that wasn't previously used. I'm assuming this would keep

q1possible[randIndex] from repeating with the same index.

As you probably know. Rand isn't really random and each time you run it that way you'll get the same results. For example,

            for(int i = 0; i < 8; i++)
    {

        int randIndex = rand() %4; // generates a random number between 0 and 3
        cout << randIndex << endl;
    }

that returns
1
3
2
0
1
0
2
2
Every time I run it on my machine. Even if I changed it to the original 4 iterations and then run that for loop again it yields repeating values. Maybe there's a simpler way but I don't think vectors would be bad.

[ats15]

A few remarks:
1. You use the same index for the outer and inner loop. That is VERY BAD. I am surprised that your compiler did not complain about that. Or maybe it's just a typo
2. Suppose you have 4 possible answers. Store numbers 0 to 3 in a vector. The first answer can be any of those. You select it with rand()%4. If you do not want to see that answer again, you must erase the corresponding index from the vector. You are left with only 3 answers. So to select the next one, you should use rand()%3. And for the next one is rand()%2. For the last one you do not need to use rand at all, since you have only one answer left

[Little Bobby Tables]

1. You use the same index for the outer and inner loop. That is VERY BAD. I am surprised that your compiler did not complain about that. Or maybe it's just a typo

why would it? it is perfectly valid c++ to have two variables with the same name in c++

[fg109]

If he was to use vectors, why not just use random_shuffle() from algorithm instead of messing around with loops and modulus?

http://www.cplusplus.com/reference/algorithm/random_shuffle/

[seph658]

I finally got it figured out! I would very much like to thank all who offered insight/help/tips on my question. I eventually ended up using fg109's suggestion and used random_shuffle at the top of my for loop. It was more efficient for me (my opinion). I know I didn't give much code to look at or work with, but I really wanted to try and figure out as much as possible on my own.

char ans2;

for (int i = 0; i < 4; ++i)
     {
          keep.push_back(i);
     }

for(int i = 0; i < 10; i++)
{
     random_shuffle (keep.begin(), keep.end());
     cout << p2Q[i].getQuestion() << endl;

     for(int i = 0; i < 4; i++)
          {
               cout << q1Possible[keep[i]] << endl;
          }
}
     cin >> ans2;

Now, all I have left to do is figure out how to keep track of the correct answer with all the randomness going on. I'll come back for help if I run into a wall. Thanks again!