C# Small example of determining whether the input is a number

public bool isnumeric(string str)
   {
    char[] ch=new char[];
    ch=();
    for (int i = 0; i < ;i++ )
    {
        if (ch[i] < 48 || ch[i] > 57)
        {
            return false;
        }
    }
    return true;
}