Asterisk rhombus formation

// *asterisk frmtn improved

#include <iostream>

using std::cout;
using std::cin;
using std::endl;

void main()
{
    setlocale(LC_ALL, "Russian");

    int a;
    char ch = '*';

    cout << "Введите размер фигуры: "; cin >> a;
    cout << endl;


    for (int i = 0; i <= a-1; i++)
    {
        for (int j = a-1; j >= i; j--)
        {
        cout << " ";
        }

        for (int j = 0; j <= i; j++)
        {
            cout << ch;
        }

        cout << " ";

        for (int j = 0; j <= i; j++)
        {
            cout << ch;
        }

        cout << endl;
    }

    cout << endl;

    for (int i = a-1; i >= 0; i--)
    {
        for (int j = a-1; j >= i; j--)
        {
            cout << " ";
        }

        for (int j = 0; j <= i; j++)
        {
            cout << ch;
        }

        cout << " ";

        for (int j = 0; j <= i; j++)
        {
            cout << ch;
        }

        cout << endl;

    }

    cout << endl;
}