coin tossing

[rrifai]

I want to create a program where the user enters the number of trial, where each trial is tossing a coin 5 time. I then want the program to display the percentage of all 5 tosses being heads in a trail. I am having trouble with the counter++, I want it to count when all 5 tosses are heads.

  #include <iostream>
#include <cstdlib>
using namespace std;

int main() {
    int n, toss;
    double counter = 0;
    cout << "Enter number of trails: ";
    cin >> n;
       for (int i = 0; i < n; i++ )
        {
            toss = rand() % 2;
            toss = rand() % 2;
            toss = rand() % 2;
            toss = rand() % 2;
            toss = rand() % 2;
    cout << "toss = "<< toss << endl;
            if ( toss == 1 ) counter++;
        }
    cout << "percentage of tossing 5 heads = "<< 100 * (counter/n) << endl;
    return 0;
};

[Moschops]

  toss = rand() % 2;
            toss = rand() % 2;
            toss = rand() % 2;
            toss = rand() % 2;
            toss = rand() % 2;

So here you toss the coin five times. But you don't look at it. You don't change the counter, you don't do anything. You just toss it five times and you only look at the outcome of the last toss. Why?

[rrifai]

toss1 = rand() % 2;
toss2 = rand() % 2;
toss3 = rand() % 2;
toss4 = rand() % 2;
toss5 = rand() % 2;


I changed it to this, but still not sure how to make a counter that counts when all tosses are heads.

[JLBorges]

#include <iostream>
#include <cstdlib>
#include <ctime>

int main() {

    std::srand( std::time(nullptr) ) ; // *** seed the random number generator

    int num_trials = 0 ;
    std::cout << "Enter number of trials: ";
    std::cin >> num_trials ;

    const int num_tosses_per_trial = 5 ; // 5 tosses per trial
    int num_trials_with_all_heads = 0 ;

    for( int i = 0 ; i < num_trials ; ++i ) { // for 'num_trials' trials

           int num_heads_for_this_trial = 0 ;

           for( int j = 0 ; j < num_tosses_per_trial ; ++j ) { // for 'num_tosses_per_trial' tosses

                // note: we are relying on the randomness of the least significant bit
                //       of a low-quality pseudo-random number generator
                const bool is_head = std::rand() % 2 == 1 ;
                if(is_head) ++num_heads_for_this_trial ;
           }

           if( num_heads_for_this_trial == num_tosses_per_trial ) ++num_trials_with_all_heads ;
    }

    if( num_trials > 0 ) {

            std::cout << "\nnumber of trials: " << num_trials << "\ntosses per trial: " << num_tosses_per_trial << '\n' ;

            const double pct_all_heads = num_trials_with_all_heads * 100.0 / num_trials ;
        
            std::cout << "percentage of " << num_tosses_per_trial << " heads in a trial : " << pct_all_heads << "%\n" ;
            
            // quick check : if num_trials is reasonably large, the actual result should be close to 
            // the computed mathematical expectation for most of the runs of the program.
            double expectation = 100.0 ;
            for( int i = 0 ; i < num_tosses_per_trial ; ++i ) expectation /= 2.0 ;
            std::cout << "mathematical expectation: " << expectation << "%\n" ;
    }
}