Thread: C++ Beginner

I am trying to write my first program in C++. I am receiving a code that I am not sure how to fix. I would appreciate the help! The code that I am receiving is : "error: expected primary-expression before "else".

Code:

// Math Program - provides quick calculations to basic math problems

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

// Function for factorial
long factorial (long a)
{
  if (a > 0)
   return (a * factorial (a-1));
  else
   return (1);
}


int main()
{

// Header to program

    cout << "******************************" << endl;
    cout << "******** Math Program ********" << endl;
    cout << "******************************" << endl << endl;
    cout << "Please choose from the following options" << endl;
    cout << "1-Factorial" << endl;
    cout << "2-Slope of a Line" << endl;
    cout << endl << "Selection: ";
    int choice;
    cin >> choice;

// Decide which function to run
    long number;


    if (choice == 1)
        {
// Enter a number and call factorial() to provide answer

            cout << endl << "Please type a number: ";
            cin >> number;
                if(number < 0)
                {
                    cout << "Enter a positive integer!..." << endl <<endl;
                }
                else
                {
                    cout << number << "! = " << factorial (number) << endl << endl;
                }
        }

long x1,x2,y1,y2;
long slope;

    else if (choice == 2)

// Enter coordinates and calculuates slope to provide answer

        {
            cout << endl << "Please enter the first set of coordinates: ";
            cin >> x1;
            cin >> y1;
            cout << endl << "Now enter the second set of coordinates: ";
            cin >> x2;
            cin >> y2;
            slope = ((y2-y1)/(x2-x1));
            cout << "The slope of the line is:" << slope;
        }

// Wait for user to respond to quit program

system ("pause");
return 0;

I am getting the error after the else( choice ==2) portion