c# Method to return a string?

I'm assuming you need to return the string constructed in your loop (and not just some arbitrary string as in the other answers). You need to build a string instead of just writing the strings out, then return that string:

public string BLoop()
{
    var builder = new StringBuilder();
    for (int i = 99; i > 0; i--)
    {
        builder.AppendLine(string.Format("{0} bottles of beer on the wall, {0} bottles of beer.", i));
        builder.AppendLine(string.Format("Take one down, pass it around, {0} bottles of beer on the wall.", i-1));
    }

    return builder.ToString();
}

Note that I've also amended the second line of your loop to eliminate the redundant String.Format parameter.

If you want to return a string, than just add a return statement

public string BLoop()
{
        for (int i = 99; i > 0; i--)
        {
            Console.WriteLine(string.Format("{0} bottles of beer on the wall, {0}   bottles of beer.", i));
            Console.WriteLine(string.Format("Take one down, pass it around, {1} bottles of beer on the wall.", i, i - 1));
            Console.WriteLine();
        }
    return "a string";
}

You could use the return keyword:

public string BLoop()
{
    for (int i = 99; i > 0; i--)
    {
        Console.WriteLine(string.Format("{0} bottles of beer on the wall, {0}   bottles of beer.", i));
        Console.WriteLine(string.Format("Take one down, pass it around, {1} bottles of beer on the wall.", i, i - 1));
        Console.WriteLine();
    }

    return "this is some string to return";
}

Use StringBuilder to build string in your loop and then return its string value.

public string BLoop()
{
    StringBuilder sb = new StringBuilder();
    for (int i = 99; i > 0; i--)
    {
        sb.AppendLine(string.Format("{0} bottles of beer on the wall, {0}   bottles of beer.", i));
        sb.AppendLine(string.Format("Take one down, pass it around, {1} bottles of beer on the wall.", i, i - 1));
        sb.AppendLine(Environment.NewLine);
    }
    return sb.ToString();
}

No clue what you're actually asking for, but if you're supposed to return the entire song as a big string then do this:

public string BLoop()
{
    var song = new System.Text.StringBuilder();
    for (int i = 99; i > 0; i--)
    {
        song.AppendLine(string.Format("{0} bottles of beer on the wall, {0} bottles of beer.", i));
        song.AppendLine(string.Format("Take one down, pass it around, {1} bottles of beer on the wall.", i, i - 1));
        song.AppendLine();
    }
    return song.ToString();
}

Hope this helps...good luck!

It's just another answer of a simplest question. Use 'return' statement after the loop.

    public string BLoop()
    {
        string sStatus = "Process Started";
        Console.WriteLine(sStatus);

        for (int i = 99; i > 0; i--)
        {
            Console.WriteLine(string.Format("{0} bottles of beer on the wall, {0}   bottles of beer.", i));
            Console.WriteLine(string.Format("Take one down, pass it around, {1} bottles of beer on the wall.", i, i - 1));
            Console.WriteLine();
        }

        sStatus = "Process Completed";
        return sStatus;
    }