Question

I’m fairly new to Stack Overflow as well as C programming, hope I don’t annoy anyone with lack of knowledge.

I’m creating an average calculator for Kickstarter projects, what I was wondering is why the method below doesn’t work. Not the average but why backers and money come out doubled if you were to enter 1 backer and $10 pledged each day,

    #include <stdio.h>
    #include <conio.h>

    int main(void){

    int loopcount = 0;
    int backers = 0;
    int money = 0;
    int average = 0;

    int tbackers = 0;
    int tmoney = 0;

    while(loopcount<5){

       //Ask for # of backers and total money pledged.
       printf("Please Enter the number of backers today, then the total money pledged                                today:\n");
       scanf("%d\n%d", &backers, &money);

       //
       backers += backers;
       money += money;


       loopcount++;
        }
       //average = tmoney / tbackers;
       printf("There were %d backers and the total collected was $%d.\nSo the average amount pledged was  $%d", backers, money, average);

       getch();

}

but the following works fine

#include <stdio.h>
#include <conio.h>

int main(void){

    int loopcount = 0;
    int backers = 0;
    int money = 0;
    int average = 0;

    int tbackers = 0;
    int tmoney = 0;

    while(loopcount<5){

       //Ask for # of backers and total money pledged.
       printf("Please Enter the number of backers today, then the total money pledged today:\n");
       scanf("%d\n%d", &backers, &money);

       //
       tbackers += backers;
       tmoney += money;


       loopcount++;
    }
       //average = tmoney / tbackers;
       printf("There were %d backers and the total collected was $%d.\nSo the average amount pledged was  $%d", tbackers, tmoney, average);

       getch();

}

Answer 1

In the first case, after each calculation, you override the value when you get a new user input:

scanf("%d\n%d", &backers, &money);

For example:

line                  | backers    | money
----------------------+------------+------
user input 5 3        | 5          | 3
backers += backers    | 10         | 3
money += money        | 10         | 6
user input 8 6        | 8          | 6
backers += backers    | 16         | 6
money += money        | 16         | 12

Now, in the second example, you don’t override the values, but add them to the sum:

line                  | backers    | money    | tbackers   | tmoney    
----------------------+------------+----------+------------+---------
user input 5 3        | 5          | 3        | 0          | 0
tbackers += backers   | 5          | 3        | 5          | 0
tmoney += money       | 5          | 3        | 5          | 3
user input 8 6        | 8          | 6        | 5          | 3
tbackers += backers   | 8          | 6        | 13         | 3
tmoney += money       | 8          | 6        | 13         | 9