Adding looped data read from a file

[Mack41]

Hi I am new to C++ and have been having trouble with this one program. I need to add up different totals calculated in if/while statements from a loop. I am unable to create a formula that works correctly. Any help would be great thanks!

(in my code it is lines 40 and 41 that are causing me difficulty)
(also for the Alumni.txt file that I am attempting to read I am using the following sets of numbers 4000 1
5500 2
33 1
6000 3
516 1
555 2
100 3
6800 3
7000 1
50 2
25 3
75 2
and am successful in everything but summing the total donations and then finding the average)

#include<fstream>
#include<iostream>
#include<cmath>

using namespace std;
int main ()
{
    double donation_amount, donation_type, donation_total, donation_sum, average;
    int counter=0;
    
    ifstream fin;
    fin.open("Alumni.txt");
    ofstream outfile;
    outfile.open("Donations.txt");
    
    if(fin.fail())
    {
                  cout<<"file did not open for reading"<<endl;
                  system("pause");
                  return 0;
                  }
   
   while(fin>>donation_amount>>donation_type)
   {
       if(donation_type==1)
           {donation_total=donation_amount;
           cout << "Straight donation of "<< donation_total << " \n";}
       else if(donation_type==2)
           {donation_total=donation_amount*2.0;
           cout << "Original donation of " << donation_amount <<" matched by NU for total of "<< donation_total << " \n";}
       else if(donation_type==3)
           {donation_total=donation_amount*3.0;
           cout << "Original donation of "<< donation_amount << "Donation matched by NU and alumni's company for total of "<< donation_total << " \n";}
           
           }
           
   donation_sum=donation_total++;
   average=(donation_sum/(2.0));
   
   cout << "the total donations are "<< donation_sum <<" and the average donation is " <<average<< endl;
   outfile<<"the total donations are "<<donation_sum<<" and the average donation is " <<average<< endl;
   
   outfile.close();
   
   system("pause");
   
   return 0;
}

[hanst99]

Your problem is that you don't really keep track of the total amount of donations, and the number of donations made.

[D80DSL3A]

Specifically, you want to increment the value of donation_total each time a donation amount is read. You are presently re-assigning the value. Example from line 26 of your code:
donation_total=donation_amount;
This makes them equal. To ADD donation_amount to donation_total do this:
donation_total += donation_amount;

You will want to start out with donation_total = 0, so initialize it to this where you declare the variable. The above correction should be applied to lines 29 and 32 as well.

Your average calculation looks a bit odd: average=(donation_sum/(2.0));

Shouldn't that be average=donation_total/number_of_donors; ? This pertains to the "number of donations" issue hinted at by hanst99 above. You could increment number_of_donors in your while loop.