C# 判断字符串是否左包含

//测试字符串 左包含
            //string str = "AAABBBCCC";
            //char[] ss = str.ToArray(); //0-8  字符数组
            //char[] ss1 = str.ToCharArray();//0-8  字符数组



            //给定一个字符串 AAA
            string str = "AAA";
            char[] strs = str.ToArray();
            string search = "AAsABBBCCC";

            char[] searchs = search.ToCharArray();
            int js = 0;
            for (int i = 0; i < searchs.Length; i++)
            {
                js++;
                if (i == strs.Length-1) //索引不能超过 (长度为3,索引0-2)
                {
                    MessageBox.Show("包含"); //所有都相等,并且超出索引,证明包含
                    break; 
                }
                if (searchs[i] != strs[i])  //在指定所用范围内只要有一个不相等, 证明不包含
                {
                    MessageBox.Show("不包含");
                    break;
                }

            }

         string str = "AAA"; //要搜索的字符串
            string search = "AAAsABBBCCC"; //要遍历的字符串
            for (int i = 0; i < search.Length; i++)
            {
                if (i == str.Length) //索引不能超过 (长度为3,索引0-2)
                {
                    MessageBox.Show("包含"); //所有都相等,并且超出索引,证明包含
                    break;
                }
                if (search[i] != str[i])  //在指定所用范围内只要有一个不相等, 证明不包含
                {
                    MessageBox.Show("不包含");
                    break;
                }

            }