Floating Point Error With This Code Can someone help me - c++

Question

i am facing problem with this chinese remainder theoram
i am taking an input.txt file as input
and trying to generate an output.txt file but it says floating point error. when i am running with some specific input at that time it is working but for many test cases it is not working
#include <bits/stdc++.h>
#include <fstream>
#include <iostream>
using namespace std;
int ModInverse(int a, int m)
{
a = a % m;
for(int x = 1; x < m; x++)
if(((a * x) % m) == 1) return x;
}
int findMinX(int num[], int rem[], int k) {
int prod = 1;
for(int i = 1; i <= k; i++) prod *= num[i];
int result = 0;
for(int j = 1; j <= k; j++) {
int y = prod / num[j];
result = result + rem[j] * ModInverse(y, num[j]) * y;
}
return result % prod;
}
int main() {
ifstream infile;
infile.open("input.txt");
int n;
int num[100];
int rem[100];
infile >> n;
for(int i = 0; i < n; i++) infile >> num[i];
for(int i = 0; i < n; i++) infile >> rem[i];
infile.close();
int k = sizeof(num) / sizeof(num[0]);
ofstream myfile;
myfile.open("output.txt");
myfile << findMinX(num, rem, k);
myfile.close();
return 0;
}

Answer 1

These lines:
for(int i = 1; i <= k; i++)
for(int j = 1; j <= k; j++)
will cause i and j to go out of bounds.
Array indexing starts at 0 in C++, so you should use indexes 0 to k-1.
Do this instead:
for(int i = 0; i < k; i++)
for(int j = 0; j < k; j++)
Another thing worth checking up is this function:
int ModInverse(int a, int m)
{
a = a % m;
for(int x = 1; x < m; x++)
if(((a * x) % m) == 1) return x;
}
Given the wrong input, it'll exit the loop and return nothing, which causes undefined behaviour. Validate the input and print an error message if the file contains data you can't handle.
Here's an example of an input.txt that makes it crash for me:
5
1 2 3 4 5
2 3 4 5 6
Another cause for concern is that you use k instead of n in your call to the function:
myfile << findMinX(num, rem, k);
This means the function will always work on 100 values. Some of them may be uninitialized, and again, undefined behaviour.