The value of integer is changing without any calculation

I have no idea why suddenly the value of integer is changing even though there’s no process of caluclation, here’s the code of my program :

#include <iostream>
using namespace std;

int main()
{
    int n;

    int a[] = {};
    int b[] = {};

    cin >> n;
    cout << "\n";

    for(int i=0;i<n;i++)
        cin >> a[i];

    cout << "\n";

    for(int i=0;i<n;i++)
        cin >> b[i];

    cout << "\n";

    for(int i=0;i<n;i++)
        cout << a[i] << " " << b[i] << "\n";

    cout << n;
}

So if I input the value of n lower than 5, there’s no problem with the code. But if I put the value of n higher than 4, the value of integer a[i] will follow the value of b[i] somehow and the value of n is different from what I input.
As for example it’s like this
Input :

10

1
2
3
4
5
6
7
8

91
92
93
94
95
96
97
98

Output :

95 91
96 92
97 93
98 94
5 95
6 96
7 97
8 98
8

As you can see the value of n changing from 10 to 8, and the loop only happen for 8 times. Why the value of n and a[i] are changing? Any help is appreciated, thanks

>Solution :

These declarations

int a[] = {};
int b[] = {};

invoke undefined behavior because you may not declare arrays with the number of elements equal to 0.

It seems you are trying to use variable length arrays that is not a standard C++ feature.

Nevertheless if the compiler supports this feature then you need at least to write

int n;

cin >> n;
cout << "\n";

int a[n];
int b[n];

for(int i=0;i<n;i++)
    cin >> a[i];

That is you may declare the arrays after the variable n will have a positive value.

But it is much better not to use non-standard language extensions. So instead of the variable length arrays you should use the standard container std::vector<int>.