//gathers and parses the users input and determines if it is "good" input
public string PostFixInput(string userinput)
{
string e; // this will be our error message
if ((userinput == null) || (userinput == "" || (userinput == " "))) // we will not tolerate nulls or empty inputs
{
e = "Null or the empty string are not valid postfix expressions.";
Mystack.Clear();
return(e);
}
// Mystack.Clear();
string s;//determines action for the digits
double a = 0.0;
double b = 0.0;
double c = 0.0;
char[] deliChars = { ' ' }; ///parses based on spaces between the variables
string[] vari = userinput.Split(deliChars);
try //now is the first part of the string really a double, or are you just testing our program
{
a = Convert.ToDouble(vari[0]);
Mystack.Push(a);
}
catch (FormatException)
{
e = "Improper input format. Stack became empty when expecting first operand.";
Mystack.Pop();
return(e);
}
try// now is the second part of the string reallly a double, or you trying to trick us
{
b = Convert.ToDouble(vari[1]);
Mystack.Push(b);
}
catch (FormatException)
{
e = "Improper input format. Stack became empty when expecting second operand.";
Mystack.Pop();
return(e);
}
s = vari[2];
Mystack.Push(s);
if (s.Length > 1) // checks to see if the last bit of the string is an operator, if you "accidently" put more chars this catches that
{
e = "Input Error " + s + " is not an allowed number or operator";
Mystack.Pop();
return(e);
}
else if (s.Equals("+") || s.Equals("-") || s.Equals("*") || s.Equals("/")) // allows the following
{
c = DoOperation(a, b, s);
Mystack.Push(c);
return(c.ToString());
}
else // you must have not done the above else if statement to get here
{
e = "Improper operator: " + s + ", is not one of +, -, *, or /";
return(e);
}
}