如何在不使用C#中的indexof方法的情况下从字符串中查找子字符串？

string str = "This is a sample string";
string subStr = "sample";

for (int i = 0; i <= str.Length - subStr.Length; i++)
{
    int j;
    for (j = 0; j < subStr.Length; j++)
    {
        if (str[i + j] != subStr[j])
            break;
    }
    if (j == subStr.Length)
    {
        Console.WriteLine("子字符串在位置：" + i);
        break;
    }
}

string str = "This is a sample string";
string subStr = "sample";

if (str.Contains(subStr))
{
    for (int i = 0; i <= str.Length - subStr.Length; i++)
    {
        int j;
        for (j = 0; j < subStr.Length; j++)
        {
            if (str[i + j] != subStr[j])
                break;
        }
        if (j == subStr.Length)
        {
            Console.WriteLine("子字符串在位置：" + i);
            break;
        }
    }
}