主要是找到菱形的规律，看每行需要的空格和星号有多少。

#include<iostream>
using namespace std;

int main()
{
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int n; cin >> n;
	if (n <= 1 || n >= 100) return 0;

	for (int i = 1; i <= n; ++i)//前n行
	{
		for (int j = 1; j <= n - i; ++j)
		{
			cout << " ";
		}

		for (int k = 1; k <= 2*i-1; ++k)
		{
			cout << "*";
		}
		cout << '\n';
	}

	for (int i = n - 1; i > 0; --i)//后面n-1行
	{
		for (int j = 1; j <= n - i; ++j)
		{
			cout << " ";
		}

		for (int k = 1; k <= 2 * i - 1; ++k)
		{
			cout << "*";
		}
		cout << '\n';
	}
	return 0;
}