non global variables

I'm using the Dev C++ 5 compiler and for all the time I've been programming I've been using global variables. I've always read that it's dangerous and now I've come across a time when errors have occured. The problem is that I can seem to be able to use a variable from int main() without causing errors.

Code:

#include <iostream>
using namespace std;
void function(int x);

void function(int x)
{
     x = 5;
     cout<<x;
     cin.get();
}

int main()
{
    int x;
    function();
}

when i try compiling this the errors:
In functionmain too few arguements to function void function[int]
at this point in file.

Code:

#include <iostream>
using namespace std;
void function(int x);

void function(int x)
{
     x = 5;
     cout<<x;
     cin.get();
}

int main()
{
    int x;
    function(int x);
}

And this says:
syntax error before ) token

Please tell me what is wrong and how to do it.
Thanks in advance

You don't need to specify the type on an actual parameter only on the formal parameter:

Code:

#include <iostream>
using namespace std;
void function(int x);

void function(int x)
{
     x = 5;
     cout<<x;
     cin.get();
}

int main()
{
    int x;
    function(x);
}

This passes a copy of x to function(). Since its a copy any changes made to x inside of function() do not affect the x inside of main(). This is known as passing by value.

To have function() affect a change upon the variable x in main() you need to pass a reference. To do that you have to change function() to accept a reference like so:

Code:

void function(int &x)

Now any changes made to x inside of function() affect the variable that was passed into it. Its important to note that the names do not matter. To see this try running the following:

Code:

#include <iostream>
using namespace std;
void function(int x);

void function(int x)
{
     x = 5;
     cout<<x<<endl;
}

int main()
{
    int z;
    function(z);
    cout<<z<<endl;
    cin.get();
}