Including multiple files with C++ - c++

Question

This week my class took a spin and is teaching material not found in the book. I'm using Visual Studio 2010, the project is to take 5 numbers from the keyboard and get the average, but I have to use functions with a .h header file and corresponding .cpp file to receive credit. This is what I have so far
Main.cpp
#include <iostream>
#include "average.h"
using namespace std;
const int numbersinput=5;
int main ()
{
int numbers,sum,avg;
cout << "Hello, please enter 5 numbers you would like to see the average for." << endl;
for (int i = 0; i != numbersinput; ++i)
{
cin >> numbers;
sum += numbers;
}
int average(int sum);
cout << avg;
system ("PAUSE");
return 0;
}
The .h headerfile named average.h
#include <iostream>
using namespace std;
int average(int);
and the other .cpp file named average.cpp
#include <iostream>
#include "average.h"
using namespace std;
const int numbersinput=5;
int avg;
int average(int sum)
{
avg = sum /numbersinput;
return avg;
}
I can get a successful build, but I get this error after I enter the first number and press enter.
Run-Time Check Failure #3 - The variable 'sum' is being used without
being initialized.
What am I not getting here?

Answer 1

You might want to initialize sum to 0 before you start adding to it with +=:
So instead of int numbers,sum,avg;
You will have int sum = 0; etc.

Answer 2

Change this line:
int numbers,sum,avg;
To:
int numbers=0;
int sum=0;
int avg=0;
This gives the variables values- before they are initialized (given a value) they are undefined, which means that they could equal any value. By initializing them, you are giving them a number to add to when you make the sum.
Edit these lines:
int average(int sum);
cout << avg;
To:
cout << average(sum);
The function declaration for int average(int sum) is not called in the same way as it is declared. The ints are unnecessary. In my edited code, you can see that the returned value (average)is printed out, instead of being left without being used.
Also, as a general tip, try not to give variables the same name. Try to make the function variable sum be called sumToAverage or instead make the sum in main be called total. It is a good idea to pick variable names that are different, so you won't get confused.

Answer 3

You're saying :
sum += numbers
But you haven't initialized sum, so it will have some random value that's on the stack. Change your declaration of sum to:
int sum = 0;
Also, you're using global variables to pass information to functions, which isn't a good idea. Get rid of the avg variable and change average to:
int average(int sum, int numberofvalues)
{
int avg = sum / numberofvalues;
return avg;
}
You're also re-declared average in the body of main, which you don't need to do as it's in the header. Then, you can get the average in main by saying:
int avg = average(sum, numbersinput);
Now, main will look like this:
int main ()
{
int sum=0;
cout << "Hello, please enter 5 numbers you would like to see the average for." << endl;
for (int i = 0; i != numbersinput; ++i)
{
int number;
cin >> number;
sum += number;
}
int avg = average(sum, numbersinput);
cout << avg;
system ("PAUSE");
return 0;
}
Oh, and don't put using namespace std in header files!