How do I return the sum of two perfect numbers in C

Question

I have a method named henry that takes two integer arguments, i and j, and returns the sum of the ith and jth perfect numbers. For example, henry(1, 3) should return 502 because 6 is the 1st perfect number and 496 is the 3rd perfect number and 6 + 496 = 502.

int henry (int i, int j)
 {
      //how do i start 
 }

I know how to print perfect number like this:

int main()  
{  
    int i, j, n, sum = 0;  

    /* Reads upper limit to print perfect numbers upto */  
    printf("Enter any number to print perfect number up to: ");  
    scanf("%d", &n);  



    printf("\nAll Perfect numbers between 1 to %d:\n", n);  


    /* 
     * Iterates from 1 to n and print if it is perfect number 
     */  
    for(i=1; i<=n; i++)  
    {  
        sum = 0;  

        /* 
         * Checks whether the current number i is Perfect number or not 
         */  
        for(j=1; j<i; j++)  
        {  
            if(i%j==0)  
            {  
                sum += j;  
            }  
        }  

        /* If the current number i is Perfect number */  
        if(sum == i)  
        {  
            printf("%d is Perfect Number\n", i);  
        }  
    }  

    return 0;  
}

Please give me hint to solve this problem, thank you.

The algorithm you have used here is very slow, and I think you won't find more than 4 (6, 28, 496, 8128) — 0xEDD1E, Apr 05 '16 at 16:46
Start by changing the `i` and `j` arguments for `henry` to something else, such as `a` and `b` that do not conflict with the `i` and `j` used in your perfect sum testing that will have to implemented in `henry`. It might then be clearer how to solve it. — Weather Vane, Apr 05 '16 at 16:56

Shubham Agrawal · Answer 1 · 2016-04-05T17:15:00.160

1

int henry(int i,int j)
{
int count=0,k=1,s=0;
  while(count<=i || count<=j)
  {
   int sum=0;
   for(p=1; p<=k/2; p++)  
    {  
        if(k%p==0)  
        {  
            sum += p;  
        }  
    }
   if(sum==k)
   count++;
   if(count==i||count==j)
   s+=k;
   k++;
  }
if(i!=j)
return s;
else
return 2*s;
}

edited Apr 05 '16 at 17:15

answered Apr 05 '16 at 16:57

Shubham Agrawal

559
6
15

if `i == j` your function returns `ith perfect_number` instead of `2* ith perfect_number` – Ingo Leonhardt Apr 05 '16 at 17:02
..and: you must `k++` after incrementing `s` – Ingo Leonhardt Apr 05 '16 at 17:09
Could use more clear formatting (and overflow detection) - other than that, nice answer. – chux - Reinstate Monica Apr 05 '16 at 18:30

How do I return the sum of two perfect numbers in C

1 Answers1