i dont know wat is wrong with my code. when i compile. i get the error

saying line 29: error: expression must have pointer-to-object type

#include <iostream>

using namespace std;

#include <vector>

double* median(double a[], int a_size) // Function Median

{ // Start of Function ( Median )

double* median;

int i,j;

double temp;

int numbers; // Variable Declared Median

if (a_size == 0) // Start of If Statement

return NULL; // if the size of the array is zero the pointer returns NULL

for (i = a_size-1; i >= 0; i--) //sorts out the array in an ascending order

{ // Start of For Loop

for (j = 1; j <= i; j++) // For Loop

{

if (a[j-1] > a[j]) // If Statement to Check the VAlue of A

{ // Start of IF Statement

temp = a[j-1]; // Assign Temp value to a

a[j-1] = a[j]; // Array in Descending Order

a[j] = temp; // Assign array to Temp

} // close of IF Statement

} // Close of For Loop

} // close of For in For Loop

//if the size is even number than takes the average else returns the middle number

if (a_size % 2 == 0) //compares the size for even number

median = ((numbers[a_size/2]) + (numbers[(a_size+1)/2])/2);// Define Median

else // else odd size

median = numbers[a_size+1]; // Assgin median for Odd Number of Array

return median; // Return Median value to Main

} // Close of Function ( Median )

int main() // Function main

{

int first;

int num2;

int i; // Variable Declared ( int )

int Exit; // Variable Declared ( Dummy )

cout << "Enter The Length of First vector"; // Output Statement for the Length of 1st Vector

cin >> first; // User Input for the Length of 1st Vector

cout<<endl; // Blank Line

vector <int> a(first); // Vector First

for (i=0; i<first; i++) // Start of For Loop for User Input 1st Vector

{

cout<< "Please enter element "<<i+1<<" of the First Vector";// Output For Entering Vector

cin>>num2; // User Input

cout<<endl; // Blank Line

a[i] = num2; // Adding Element in Vector A

}

cout <<"The Median of the Data is :" << median*(a, first) << "\n"; //Displays the Medianimum value out of the array

cout<<" Please Enter Any Key to Exit";

cin>>Exit;

return 0;

}