passing class

how can i pass a class variable to a public function of the class and then return the class variable with the modifications?

You don't need to pass a class variable to a class function. The class function has access to all class data variables already. like this:

Code:

#include <iostream.h>

class Sample
{
  public:
    Sample();
    int getData();
    void ModifyData();
  private:
    int data;
};

Sample::Sample() : data(3)
{}

int Sample::getData()
{
  return data;
}

void Sample::ModifyData()
{
  data += 4;
}

int main()
{
  Sample sample;
  cout << "data before modification = " << sample.getData() << endl;
  sample.ModifyData();
  cout << "data after modification = " << sample.getData() << endl;
  return 0;
}

if you want to display modified variable directly from ModifyData you could do this:

Code:

#include <iostream.h>

class Sample
{
  public:
    Sample();
    int getData();
    int ModifyData();
  private:
    int data;
};

Sample::Sample() : data(3)
{}

int Sample::getData()
{
  return data;
}

int Sample:: ModifyData()
{
  data += 4;
  return data;
}

int main()
{
  Sample sample;
  cout << "data before modification = " << sample.getData() << endl;
  cout << "data after modification = " << sample.ModifyData() << endl;
  return 0;
}