Passings Array by Refernce

[brycematheson]

I am absolutely HORRIBLE at passing functions, and even more so with passing arrays. I'm trying to pass my "grades" array to the other functions, but I know I have to do it by reference since I can't return it. Can someone help shed some light?

#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;

int readFile(int, int &count, int (&grades [10]));
int writeFile();
int averageGrades(int, int);

/**********************************************************************
* Reads an external file of grades and then returns those values to
* other functions in the program.
*********************************************************************/
int readFile(int sum, int &count, int (&grades [10]))
{
   //Declare variable
   char sourceFile[16];
   ifstream inStream;

   //Asking for user input
   cout << "Source file: ";
   cin >> sourceFile;

   //Open file
   inStream.open(sourceFile);
   if (inStream.fail())
   {
      cout << "Input file opening failed.\n";
      exit(1);
   }

   //Read from file and place in array
   for (int i = 0; i < 10 && inStream >> grades[i]; i++)
   {
      if (grades[i] == -1)
      {
         count++;
      }

      if (grades[i] != -1)
      {
         sum += grades[i];
      }
   }
   return sum;
}

/**********************************************************************
 * Reads an external file of grades and then returns those values to
 * other functions in the program.
 *********************************************************************/
int writeFile()
{
   ofstream outStream;
   char destinationFile[16];

   //Asking for user input
   cout << "Destination file: ";
   cin >> destinationFile;

   //Open file
   outStream.open(destinationFile);
   if (outStream.fail())
   {
      cout << "Output file opening failed.\n";
      exit(1);
   }

   outStream << grades[i];

   return 0;
}


/**********************************************************************
* Finds the average of the ten grades from the previous function.
***********************************************************************/
int averageGrades(int sum, int count, int average)
{
   //The magic formula to find the average
   if (count == 10)
   {
      cout << "Average Grade: ---%" << endl;
   }

   else
   {
      average = (sum / (10 - count));
      cout << "Average Grade: " << average << "%" << endl;
   }

   return average;
}


/**********************************************************************
* Basically a delegator. Calls other functions to do its dirty work.
***********************************************************************/
int main()
{
   //Declaring Variables
   int average = 0;
   int sum = 0;
   int count = 0;
   int grades[10];

   //Calling other functions
   sum = readFile(sum, count);
   average = averageGrades(sum, count, average);

   return 0;
}

[gerard4143]

Here's a simple way to pass an array.

#include <iostream>

void myfunc(int * x)
{
	for (int i = 0; i < 7; ++i)
		std::cout << x[i] << std::endl;
}

int main()
{
	int mya[] = {1, 2, 3, 4, 5, 6, 7};

	myfunc(mya);
	return 0;
}

[NathanOliver]

To expand on what Gerard pointed out is when you pass an array to a function it actually only passes a pointer to the first element. Since you are working with pointers any change to a value in the array in a function is reflected in main.

void foo(int[]);
// or
void foo(int[SOME_NUMBER]);

// is the same as
void foo(int *);

[arkoenig]

I'm going to disagree with both gerard4143 and NathanOliver here. You can pass an array by reference as follows:

1) Change line 14 to the following:

int readFile(int sum, int &count, int (&grades) [10])

In case you're wondering what I changed, I moved one parenthesis.

2) Change line 107 to the following:

sum = readfile(sum, count, grades);

There may be other errors, but with a little luck, these suggestions will get you started in the right direction.

[NathanOliver]

But there is no need for him to pass it by reference. I'm not saying you cant but asking why you would want to.

[arkoenig]

But there is no need for him to pass it by reference. I'm not saying you cant but asking why you would want to.

I have no idea :) Perhaps part of the original problem was to learn something about references.

I was just answering the question that was asked.