C++- Filling a 2D array from user input

I’m new to programming and was finding transpose of a matrix.
However, I want the input of the matrix from the user and by writing the following code, the complier doesn’t take any input values and immediately stops.
I looked into previous questions posted here about the same but found non useful.

#include<iostream>
using namespace std;
int main()
{
    int rows,val;
    int num[rows][rows];
    cin>> rows;
    for(int i=1; i<= rows; i++)
    {
        for(int j = 1; j <= rows; j++)
        {
            cin>> val;
            arr[i][j]= val;
        }
        cout<<endl;
    }

>Solution :

1. You can’t use variables in array length if they aren’t defined as one of the comments mentioned.
2. arr[i][j] inside your nested for loop isn’t declared so that would also give an error, I guess you wanted to use num array which you declared.
   The rest is all looking good