CODEWITHSUNDEEP
c++
2012ssohn
2012ssohn

Reputation: 159

Program Continues to Crash [Project Euler #21]

I'm running this program in C++ to find the sum of all amicable numbers below 10000. Yes, this is my program for Project Euler question 21. I already know that the algorithm is not the most efficient one, and the reason I'm posting this has nothing to do with the efficiency of the program.

Code:

#include <iostream>
#include <math.h>
using namespace std;

int main()
{
  int sum = 0;
  int d[10000];
  for (int i = 0; i <= 9999; i++)
    d[i] = 0;
  for (int i = 1; i <= 9999; i++)
    for (int j = 1; j < i; j++)
      if (i%j == 0)
        d[i] += j;
  for (int i = 1; i <= 9999; i++)
    if (d[d[i]] == i)
      sum += i;
  cout << sum/2;
}

The error seems to occur in the last for loop - I commented it out and everything runs fine (other than, of course, giving the obviously wrong result of 0). The error message I get is this

enter image description here

followed by this:

----jGRASP exec: C:\Users\Sam\Documents\Project Euler\problem.exe

----jGRASP wedge2: exit code for process is -1073741819.
----jGRASP: operation complete.

And now for the obvious question - WHY is this error happening?

Upvotes: 1

Views: 184

Answers (2)

Chris Bogart
Chris Bogart

Reputation: 472

If d[i] ever gets a value greater than 10000, then d[d[i]] will be a reference outside the 10000 integers you've allocated. That'll cause an error.

Upvotes: 0

R Sahu
R Sahu

Reputation: 206607

This line

 if ( d[d[i]] == i)

is going access d beyond the valid range of indices since d[i] can be greater than 9999. Change it to:

 if ( d[i] <= 9999 && d[d[i]] == i)

Upvotes: 2

Related Questions