Question

I am trying to run a program and SOMETIMES I’m getting this error when trying to compile

ld returned 1 exit status

Although, when it compiles (like I said, not always) and trying to put certain input, the program outputs the answer… and then crashes. Is there any way is this possible at all?

Here is my code:

#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;

int main() {
  bool flag;
  int n,x[] = {1,-1};
  long long int A,cont,mul,acum;
  while(cin >> n >> A) {
    acum = 0;
    vector<long long int> nums(n),nums2;
    for(int i=0;i<n;i++) cin >> nums[i];

    sort(nums.begin(),nums.end());

    for(int i=n-1;i>=0;i--) {
      flag = 1;
      for(int j=0;j<i and flag;j++) if(nums[i]%nums[j] == 0) flag = 0;
      if(flag) nums2.push_back(nums[i]);
    }

    n = nums2.size();

    vector<long long int> mult(n,0);

    const long long int num = (1<<n);
    for(int i=0;i<num;i++) {
      cont = 0, mul = 1;
      for(int j=n-1;j>=0;j--) if(i & (1<<j)) cont++, mul *= nums2[j];
      mult[cont-1] += A/mul;
    }

    for(int i=0;i<n;i++) acum += (x[i%2]*mult[i]);

    cout << acum << endl;
  }
  return 0;
}

and this is the input I put when the program crashes:

17 1000
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Answer 1

If you run your program in a debugger, you’ll see that the problem occurs on the line

mult[cont-1] += A/mul;

when cont is 0, which means that you are trying to modify element -1 of the vector.

I can’t tell what the algorithm is trying to do, so I can’t tell why cont might end up zero.

Overall advice: Learn to use a debugger. It’s your friend. 🙂