Help with Vector Median

[Xavier3MG]

Hi there, I am pretty new here. I need some help with this statistics program i am writing for a c++ class I am taking. We are using Code Blocks 13.12. I am stuck on the median function. I wrote it and am not getting any errors or warnings.


For some reason the median always returns the same thing no matter the input:
6.9531e-308

What does this mean? Is this an error? What did I do wrong writing the median function?

#include <iostream>
#include <vector>


using namespace std;
void mysort(vector<int> &v);
double average (vector<int> v);
double median (vector<int>v);
int main(){

    int size, i, data, n;
    double mean, median;



    cout << "Please Enter the desired size of your array: ";
    cin >> size;

    vector<int>name(size);
    for (i=0; i < name.size(); i++) {
        cout << "array[" << i << "]: ";
        cin >> data;
        name[i] = data;

    }



    cout << "Sort: "; //sorts the array from least to greatest

    for (i=0; i < name.size(); i++) {
       mysort (name);

        cout << name[i] << ", ";
    }
    cout << '\n';
    cout << '\n';

    cout << "n: " << name.size() << '\n'; //returns size of array

    cout << '\n';

    mean = average (name);
    cout << "mean: " << mean << '\n'; //returns average



    cout << '\n';

    cout << "variance: " << '\n'; //sample variance

    cout << '\n';

    cout << "min: " << name[0] << '\n'; //returns min

    cout << '\n';

    cout << "q1: " << '\n'; //q1

    cout << '\n';

    cout << "median: " << median << '\n'; //returns median

    cout << '\n';

    cout << "q3: " << '\n'; //q3

    cout << '\n';

    cout << "max: " << name[name.size() - 1] << '\n'; //returns max



return 0;
}


void mysort (vector<int> &v) {
    int i, j, k;

 for (i = v.size(); i > 0; i--) {

  for (j = 0, k = 1; k < i; j++, k++) {

   if (v[j] > v[k]) {

    int temp = v[j];
    v[j] = v[k];
    v[k] = temp;
   }
  }
 }
}



double average (vector<int> v) {
    int sum = 0;
    for (int i = 0; i < v.size(); i++){
        sum += v[i];
    }
    //double average =
    return sum / v.size();

}






double median (vector<int>v) {
    double median;
    if ((v.size() % 2) == 0) {
        median = (v[(v.size() / 2) - 1] + v[v.size() / 2]) / 2;
    }
    else {
        median = v[v.size() / 2];
    }
    return median;

}

[mutexe]

Here's a nice hint from my compiler:

(62): error C4700: uninitialized local variable 'median' used

[Xavier3MG]

could you tell me a bit more about what that means? does that mean i forgot to put something in or i put too many things in?

[mutexe]

you never assign anything to your median variable, and you didnt initialise it so you're always gonna get garbage. effectively you've done this:

#include<iostream>

int main()
{
	double median;

	std::cout << median << std::endl;

	return 0;
}

You've written a function to calculate it, but you never call it.

[Xavier3MG]

what i changed is this:

#include <iostream>
#include <vector>

using namespace std;

double middle;
int main() {
middle = median (name);
cout << "median: " << name[middle] << '\n';
 
}

double median (vector<int>v) {

if ((v.size() % 2) == 0) {
        median = (v[v.size() / 2 - 1] + v[v.size() / 2] ) / 2;
}
else {
median = v[v.size() / 2];
}
return median;
}

how does look? its now returning like 3,714,000......

[mutexe]

how does look?

No offence, but it's terrible.
You're making the same mistake with your name variable (not even declaring it, let alone initialising it).

its now returning like 3,714,000

Your code does not even compile, so how on earth are you getting any results?
I suggest going through some of the tutorials on this site.