Random array selector

Question

I'm trying to make a workout program that selects a random workout and musclegroup every time you start it. I have ran into trouble with selecting which musclegroup it's picking.

I would like it to pick one of the three arrays but right now the value of dice_roll is always equal to 2. Not sure where I have gone wrong. Thanks for any help.

(OBS! Excuse my ugly code, it doesn't seem to be posting right so it may be excused!)

int main() 
{
    int muscleGroup;
    string chest[2] = {"Benchpress 4x2", "Pushups 10x4"};
    string legs[2] = {"Squat 8x4", "Leg extension 10x3"};
    string back[2] = {"Pullup 3x8", "Rows 10x3"};
    mt19937 generator; 
  
    uniform_int_distribution<int> distribution(0, 2);
    int dice_roll = distribution(generator);
    if (dice_roll == 0) 
    {
        cout << "You are training: Chest" << endl;
        cout << "Your exercises are going to be written below!" << endl;
    } 
    else if (dice_roll == 1) 
    {
        cout << "You are training: Legs" << endl;
        cout << "Your exercises are going to be written below!" << endl;
    } 
    else if (dice_roll == 2) 
    {
        cout << "You are training: Back" << endl;
        cout << "Your exercises are going to be written below!" << endl;
    }         
  
    // cin >> test;
    return 0;
}

You need to seed the generator. Easy and ugly way is mt19937 generator(time(0)); — HolyBlackCat
– HolyBlackCat, Commented Jan 1, 2018 at 13:19

Marc · Accepted Answer · 2018-01-01 13:20:29Z

5

You need to initialize your generator with a random seed.

You can do so using:

std::random_device rd;  //Will be used to obtain a seed for the random number engine
std::mt19937 gen(rd()); //Standard mersenne_twister_engine seeded with rd()

You can find a larger code snippet and more details on the cppreference uniform_int_distribution page

answered Jan 1, 2018 at 13:20

Marc

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3 Comments

HolyBlackCat Over a year ago

Note that it won't work on MinGW, since their random_device always produces a same sequence.

Alexanderrost Over a year ago

It worked doing that! Thanks a lot, i'll have to do some reading on seeds because I have no clue why it worked.

Jesper Juhl Over a year ago

@Alexanderrost the seed is what determines the sequence of the pseudo-random generator (in your case, the mersenne twister) - you can think of it as a "starting point". Given the same seed it will always produce the same sequence of numbers (which can be very useful). Seeding it with pure entropy guarantees a unique sequence every run.

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