Reading and writing files

[ElectricClam148]

I have a program that prompts the user to enter a file name which in my case is grades1.txt which has the numbers 90 86 95 76 92 83 100 87 91 -1. Then I want it to read the file get the average of those numbers then ask the user to name a different file so those same 10 numbers can be stored in that different file. My error is that I get a segmentation fault.
This is my code so far

#include <iostream>
#include <fstream>
using namespace std;
int averageGrades(int grade[], int a);
//ask the user for the file that they want to use which in my case is grades1.txt
void readFile()
{
  ifstream instream;
  int grade[9];
  char nameofFile[256];
  cout << "Source file: ";
  cin >> nameofFile[256];
  instream.open("nameofFile[256]");
  for(int a = 0; a < 10; a++)
    instream >> grade[a];
  instream.close();
}
//ask the user to give a name of a file to create a new txt file with the same numbers as grades1.txt
void writeFile(int grade[])
{
  char fileName[256];
  ofstream outstream;
  cout << "Destination file: ";
  cin >> fileName[256];
  outstream.open("fileName[256]");
  for(int b = 0; b < 10; b++)
    outstream << grade[b];
  outstream.close();
}

//calculates the average
int averageGrades(int grade[], int a)
{
  int sum = 0;
  int j, count = 0;
  for(j = 0;j < a; j++)
    {
       sum += grade[j];
       if(grade[j] == -1)
         ;
       else
         count++;
    }
  if(sum == -10)
    return sum;
  else
    return sum / count;
}

int main()
{
  int grade[9], a;
  int quotion;
  readFile();
  quotion = averageGrades(grade, a);
  if(quotion == -10)
    cout << "Average Grade: ---%";
  else
    cout << "Average Grade: " << quotion << "%";
  writeFile(grade);
  cout << "File written successfully";
  return 0;
}

[Zhuge]

On line 55, you pass "a" as the size of the array, though it hasn't been initialized to 9 like it should be. You might also want to note that readFile() does nothing, as it simply creates and edits some local variables that are destroyed when the function closes.

[ElectricClam148]

I'm still a little confused so what do I do to fix readFile() I want it to ask the user for a specific file and then put those numbers into the array. and I did initialize it readFile() and in main.