for嵌套用法 选择图形 举例

namespace ConsoleApplication39
{
    class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                Console.Write("请选择您想要得到的图形？A正方形；B三角形；C平行四边形；D菱形；E梯形：");
            string n = Console.ReadLine();
            Console.Write("请输入数字：");
            int m = Convert.ToInt32(Console.ReadLine());
            switch (n)//选择语句
            {
                case "A":正方形
                    for (int i = 1; i <= m; i++)//列循环，一次循环出每一次的行循环，下同
                    {
                        Console.Write("☆");
                    
                        for (int j = 1; j <= m; j++)行循环
                        {
                            Console.Write("☆");
                        }
                        Console.Write("
");
                    }
                    break;
                case "B"://三角形
                    for (int i = 1; i <= m; i++)
                    {
                        for (int j = 1; j <= m - i; j++)
                        {
                            Console.Write("  ");
                        }
                        for (int k = 1; k <= 2 * i - 1; k++)
                        {
                            Console.Write("☆");
                        }
                        Console.Write("
");
                    }
                    break;
                case "C":
                    for (int i = 1; i <= m; i++)
                    {
                        for (int j = 1; j <=m-i; j++)
                        {
                            Console.Write("  ");
                        }
                        for (int k =1; k <= m; k++)
                        {
                            Console.Write("○");
                        }
                        Console.Write("
");
                    }   
                    break;
                case "D":
                    for (int i = 1; i <= m; i++)
                    {
                        for (int j = 1; j <= m - i; j++)
                        {
                            Console.Write("  ");
                        }
                        for (int k = 1; k <= 2 * i - 1; k++)
                        {
                            Console.Write("☆");
                        }
                        Console.Write("
");
                    }
                    for (int p = 1; p <= m; p++)
                    {
                        for (int q = 1; q <= p; q++)
                        {
                            Console.Write("  ");
                        }
                        for (int h = 1; h <= 2 *(m-p) - 1; h++)
                        {
                            Console.Write("★");
                        }
                        Console.Write("
");
                    }
                    break;
                case "F":
                    for (int i = 1; i <= m; i++)
                    {
                        for (int j = 1; j <= m - i; j++)
                        {
                            Console.Write("  ");
                        }
                        for (int k = 1; k <= 2 * i + 3; k++)
                        {
                            Console.Write("☆");
                        }
                        Console.Write("
");
                    }
                    break;
                default:
                     Console.Write("您的输入有误！");
                     break;
            }
            Console.ReadLine();
            }
        }
    }
}

扩展：不论方法只要能得到结果
例：

static void Main(string[] args)
        {

            string s = "";
            s = "★
★★
★★★
★★★★
★★★★★";
            Console.WriteLine(s);
            Console.ReadLine();
            
        }