Find Perfect Number generator stops at 6

This is a perfect number generator, when you start from 0 to 100 it should find 6 and 28, but for some reason it only recognizes 6 as a perfect number. Why doesn't it output 28? Danke!

Code:

---

#include <stdio.h>
#include <stdlib.h>

int check;
int isAFactor(int i, int o);



int main()
{

    int startval;
    int endval;
    int o;//outer loop
    int i = 1;//inner loop

    int check2 = 0; //if remains 0, no perfect numbers.


    int add = 0;


    printf("Enter starting integer: ");
    scanf("%d", &startval);
    printf("\nEnter ending integer: ");
    scanf("%d", &endval);

    o = startval;

    for(;o<=endval;o++)
    {
        for(; i<=o/2; i++)
        {
            check = isAFactor(i,o);

            if (check == 0)
            {
                add = add + i;
            }

        }

        if(add == o && o!=0)
        {
            printf("\n%d is a perfect number.\n", o);
            check2 = 1;
        }

    }

        if(check2 ==0)
        {
            printf("\nNo Perfect Numbers found between %d and %d.", startval, endval);
        }


    return 0;
}


int isAFactor(int i, int o)
{
    check = o%i;
    return check;
}

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My guess is that you need to have a valid starting value of 1 for i in this loop.

Code:

---

for(; i<=o/2; i++)

---

Tim S.

When I do that for some reason it doesn't find anything. I think I', asking a bit much, I did put alot of effort and thought in the program. I'll put some more in it :P

You also need to reset "add" at some point in your code.

had to make add = 0 again doh!

oopsy you answered it :P thanks for your time!

Code:

---

    o = startval;     
  for(;o<=endval;o++)   
      {
        for(; i<=o/2; i++)

---

The above is a *real bad idea* .... put the initializer for the loop *in the loop*.
What is the value of i the second time through the loop?

I've seen it on here a number of times lately, from a number of different posters.
I sincerely hope there's not some fool teacher out there advocating it!

Code:

---

for (o = startval; o < endval; o++)
  for ( i = 0; i < o /2; i++)

---

No, I teach myself. But the reason I did that is for some reason it doesn't work when I put it in there. I'm going to check it out now that it is working.

Well, I changed it to while() :S I'll put it in for()'s and see if there is any change

changed it to for() it works :)

Thanks all for your help! it is much appreciated! Sorry for anyone that leeps looking at this post bc of my replies :/