How to compile c & c++ programs?

There are several issues with your test source package.

My guess is that you are trying to compile using slightly older C++ standards (gcc instead of g++) and probably based on a Windows routine (using conio).

I've tidied up the test program for you:

#include <iostream> /* dont need .h */    
using namespace std; /* use a namespace */
/* #include <conio.h>   this is a windows header - dont need */

class fact
{
int i;
    static int count;
    public : 
    void calculate()
    {
        long int fact1=1;
        count++;
        for (i = 2; i <= count; i++)
        {
            fact1 *= i;
        }
        cout << "\nFactorial of " << count << '=' << fact1 << '\n';
    }
};
int fact :: count;

int main(void) /* you had an invalid main declaration */
{
    int i;
    /* clrscr();  not necessary */
    fact f;
    for (i = 1; i <= 15; i++)
    {
        f.calculate();
    }
    /* getch(); not necessary */

    return 0; /* need to return a standard value */
}

then compile using

g++ factorial.cpp -o factorial