Rotate main diameter 3 times A[4][4]

#include <iostream>
using namespace std;
int main()
{
    //def.
    int a[4][4], i, j;
    int b[5];
    //input.
    for (j = 0; j <= 3; j++) {
        for (i = 0; i <= 3; i++) {
            cin >> a[j][i];
        }
    }
//process.
cout << "before rotation : ";
    for (j = 0; j <= 3; j++) {
        cout << endl << endl;
        for (i = 0; i <= 3; i++) {
        cout << a[j][i] << "\t";
        }
    }
    for (i = 0; i <= 3; i++) {
        b[i] = a[i][i];
    }//transferring the values to the 1D array
    for (j = 1; j <= 3; j++) {
        for (i = 4; i >= 1; i--) {
            b[i] = b[i - 1];
        }
    b[0] = b[4];
    }//rotate
    for (i = 0; i <= 3; i++) {
        a[i][i] = b[i];
    }//transferring the values to the 2D array
//print.
cout << "\nafter rotation : ";
    for (j = 0; j <= 3; j++) {
        cout << endl << endl;
        for (i = 0; i <= 3; i++) {
            cout << a[j][i] << "\t";
        }
    }
    cout << endl;
}