i am trying to calculate the average value of a 2d array that is 400x400 elements big. for some reason i am getting a different negative value every time. here is my code i have for the program so far. the data file is too big to attach. hopefully its not necessary. the max value in the data file is 99 and no numbers are negative. eventually i will be calculating variance of a subarray.

#include <cmath>
#include <iostream>
#include <iomanip>
#include <iostream>
#include <string>
#include <fstream>
#include <string>
#include <stdlib>
using namespace std;
int const N = 400;

double calcMean (const int plot[][N]);

int main()
{
int elevation[N][N];
ifstream file1;
string filename;
int nrows, ncols;

cout << "Enter the name of the input file.\n";
cin >> filename;
file1.open(filename.c_str());
if (file1.fail())
{
cerr << "Error opening input file.\n";
return 0;
}
file1 >> nrows >> ncols;
for (int i=0; i<=nrows-1; i++)
{
for (int j=0; j<=ncols-1; j++)
{
file1 >> elevation[i][j];
}
}

cout << calcMean(elevation);

return 0;
}

double calcMean (const int plot[][N])
{
int sum = 0;
int mean = 0;
for (int r=0; r<=N-1; r++)
{
for (int c=0; c<=N-1; c++)
{
sum += plot[r][c];
mean = (sum / 160000);
}
}
return mean;
}