C# string wraps according to symbols

Examples are as follows

main code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

      

        private void button1_Click(object sender, EventArgs e)
        {
            StringBuilder P_stringbuilder = new StringBuilder(textBox1.Text);  // 创建字符串处理对象，减轻垃圾收集器的压力

            char[] punctuationMarks = { ',', '.', '?' };

            foreach (char mark in punctuationMarks)
            {
                for (int i = 0; i < P_stringbuilder.Length; i++)
                {
                    if (P_stringbuilder[i] == mark)
                    {
                        P_stringbuilder.Insert(++i, Environment.NewLine); // 向字符串中添加换行符
                    }
                }
            }

            textBox2.Text = P_stringbuilder.ToString();
        }


    }
}