Finding average of random array

Question

I'm trying to create an array that generates 20 random numbers from 0-9 using a certain random seed(which i have already), then calculates the average of the random numbers generated. I've gotten it to execute the array fine, but when i go to calculates the sum of the random numbers, it gives me back -16. I've looked at several different other things to try to help and they all have the same thing that i've got

for (i = 0; i < SIZE; i++) {
            sum += num[SIZE];}

Can someone point out what im doing wrong here or else where in the program?

#include <iostream>
#include <cstdlib>

using namespace std;

int main() // Creates the array
{
    srand(2622); // random seed 

    const int SIZE = 20;
    int num[SIZE], i, sum = 0;  


    for (i = 0; i < 20; i++) {
        cout << rand() % 10 << " : "; // generates random numbers 0-10
    }
        cout << endl;

    for (i = 0; i < SIZE; i++) {
        sum += num[SIZE];

    }
        cout << sum << endl; 


    return 0;

}

The random number generator generates only positive numbers? — Agu V
– Agu V, Commented Apr 4, 2016 at 5:00
It would be interesting to print num[SIZE] before executing last for-cycle. — maxvv
– maxvv, Commented Apr 4, 2016 at 5:17

Abhishek · Accepted Answer · 2016-04-04 06:20:06Z

2

You are missing at here --

sum += num[SIZE]; should be sum += num[i];

#include <iostream>
#include <cstdlib>

using namespace std;

int main() // Creates the array
{
    srand(2622); // random seed 

    const int SIZE = 20;
    int num[SIZE], i, sum = 0;  


    for (i = 0; i < 20; i++) {
        num[i] = rand() % 10  ;
        cout << num[i] << " : "; // generates random numbers 0-10
    }
        cout << endl;

    for (i = 0; i < SIZE ; i++ ) {
        sum += num[i];

    }
        cout << sum << endl; 


    return 0;

}

edited Apr 4, 2016 at 6:20

answered Apr 4, 2016 at 5:08

Abhishek

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2 Comments

mxrider29 Over a year ago

Thanks that was the problem!

Ajay Over a year ago

Use SIZE everywhere

Richard Hodges · Accepted Answer · 2016-04-04 09:54:23Z

Just for exposition, here's the same program using c++14 and idiomatic use of the standard library.

#include <iostream>
#include <numeric>
#include <random>
#include <functional>

using namespace std;

template<class Iter>
std::ostream& emit_range(std::ostream& os, Iter first, Iter last,
                         const char* inter_sep = " : ",
                         const char* terminator = "\n")
{
    auto sep = "";
    while (first != last) {
        os << sep << *first;
        ++first;
        sep = inter_sep;
    }
    return os << terminator;
}

int main() // Creates the array
{
    // function object to create a pre-seeded pseudo-random sequence
    auto next_number = [eng = std::default_random_engine(2622),
                 dist = std::uniform_int_distribution<int>(0, 9)]() mutable
    {
        return dist(eng);
    };

    constexpr int SIZE = 20;
    int num[SIZE];

    // generate the random numbers
    std::generate(std::begin(num), std::end(num), next_number);

    // compute the sum
    auto sum = std::accumulate(std::begin(num), std::end(num), 0,
                               std::plus<>());

    // compute the average
    auto average = double(sum) / SIZE;

    // print results    
    emit_range(cout, std::begin(num), std::end(num));
    cout << sum << endl;
    cout << average << endl;


    return 0;

}

results:

1 : 9 : 6 : 6 : 3 : 0 : 3 : 6 : 7 : 1 : 7 : 2 : 1 : 8 : 0 : 0 : 2 : 6 : 1 : 9
78
3.9

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