error: cannot run program

It says : "redefinition of formal parameter 'size'"
and: "redefinition of formal parameter 'menu'"

I tried but still cannot figure out.

#include <iostream>
#include <fstream>
#include <iomanip>
#include <string>
#include <vector>
using namespace std;

// Function of max

void loadData ( int *arr, int &size)
{
	int size=0;
	while(size != 0)
	{
	string name;
	cout <<"Enter data file name:" << endl;
	getline(cin, name);	
	ifstream inputFile;
	inputFile.open(name.c_str(), ios_base::in); // Open file

	if (inputFile.is_open())
	{
		cout <<"Finished loading data" << endl;

		int count;
		while (inputFile >> count)  // Count the numbers in the file
			size++;
		inputFile.close();

		//Create a dynamic array to hold the values
		vector<int> arr;

		//Create an input file stream
		ifstream inputFile(name.c_str(),ios::in);

		int number;  //Variable to hold each number as it is read
	
        //Read number using the extraction (>>) operator
        while (inputFile >> number) 
		{
		//Add the number to the end of the array
			arr.push_back(number);
		}

		//Close the file stream
		inputFile.close();
	}
	else 
	{
		cout <<"Cannot read the file!"<< endl;
	}
	}
}

// Function of sorting data

void sort ( int a[], int &size )
{
    bool swapped;
    do
    {
          swapped = false;
          for ( int i = 1; i < size; i++)
         {
              if ( a[i - 1] > a [i] )
              {
                    int temp = a[i-1];
                    a[i-1] = a[i];
                    a[i] = temp;
                    swapped = true;
               }
           }
           size = size -1;
   }while ( swapped );
}

// Function of showwing data

void showData ( int a[], int &size)
{
	cout << "Data:" << endl;

	for ( int i = 1; i < size; i++)
		cout <<  a[i] <<" | "<< endl;
}
int displayMenu(int &menu)
{
	cout <<"---- Main Menu ----\n"<< endl;
	cout <<"1. Load data from file\n"<< endl;
	cout <<"2. Sort data\n"<< endl;
	cout <<"3. Display data\n"<< endl;
	cout <<"4. Exit\n"<< endl;
	cout <<"Your menu choice: "<< endl;
	int menu = 0;
	cin >> menu;
	while ((menu < 1) && (menu >4)) 
	{
		cout <<"Error! "<< endl;
		cout <<"Your menu choice: "<< endl;
		cin >> menu;
	}
}

int main()
{
	int* iarr;
	int isize;
	int choice;
	while (choice = 4)
	{
		displayMenu(choice);
		if (choice = 1)
			loadData (iarr, isize);
		else if (choice = 2)
			sort (iarr, isize);
		else if (choice = 3)
			showData (iarr, isize);
	}
	return 0;
}