/// <summary>
/// Return result of exact fraction from queue of postfix.
/// </summary>
/// <param name="postFix"></param>
/// <returns></returns>
public static ProperFraction evaluatePostFix(Queue <Object> postFix)
{
if (postFix == null)
{
return(null);
}
Queue <Object> Fractionlist = new Queue <Object>();
//Cast all int64 into properFraction.
foreach (Object element in postFix)
{
if (element is Int64)
{
Fractionlist.Enqueue(new ProperFraction((Int64)element));
}
else
{
Fractionlist.Enqueue(element);
}
}
Stack <ProperFraction> nstack = new Stack <ProperFraction>();
// while it's more than one element in the queue.
while (Fractionlist.Count != 0)
{
Object obj = Fractionlist.Dequeue();
//Retrieve oldest element.
if (obj is ProperFraction) //If it's a properfraction
{
nstack.Push((ProperFraction)obj); //add to the stack.
}
else//else it must be operator
{
if (!(obj is char) || nstack.Count == 0)
{
throw new Exception("Please Debug when this error happend.");
}
//pop two numbers from the statck and evaluate.
ProperFraction secondnumber = nstack.Pop();
ProperFraction firstnumber = null;
if (nstack.Count != 0)
{
firstnumber = nstack.Pop();
}
//if cannot get the second one and there is only one element, then it must be unary operator.
// add the result to the stack.
nstack.Push(compute(firstnumber, secondnumber, (char)obj));
}
}
return(nstack.Pop());
}
public static ProperFraction operator -(ProperFraction a)
{
if (a == null)
{
throw new Exception();
}
ProperFraction pf = new ProperFraction(!a.sign);
pf.decimalpart = new ImproperFraction(a.decimalpart.getNumerator(), a.decimalpart.getDenominator());
pf.integerpart = a.integerpart;
return(pf);
}
/// <summary>
/// method is tested.
/// <para>
/// This method takes in two number and an operator and return the result.
/// </para>
/// If there is only one number is not null, this method will assume the operator is '-' or '+';
/// </summary>
/// <param name="a"></param>
/// <param name="b"></param>
/// <returns>
/// Null is the computation cannot be done or error has occured.
/// </returns>
public static ProperFraction compute(ProperFraction a, ProperFraction b, char opt)
{
// the operator is valide:
if (getOptRank(opt) == -1)
{
return(null);
}
// If there is one number at least:
if (a == null && b == null)
{
return(null);
}
//At this point, the operator will be valide and there will be at least one numebr.
if (a != null && b != null)//Both bumber is not null
{
switch (opt)
{
case '+':
return(a + b);
case '-':
return(a - b);
case '*':
return(a * b);
case '/':
return(a / b);
}
throw new Exception("Something wrong, please check consistency on logic.");
}
//One of the number is null.s
if (opt == '-')
{
return(a == null ? -b:-a);
}
if (opt == '+')
{
return(a == null ? b : a);
}
return(null);
}
public static ProperFraction evalueteStacks(Stack <ProperFraction> numberstack, Stack <char> optstack)
{
//make sure the input is both not null:
if (numberstack == null || optstack == null)
{
return(null);
}
//If there is no more operator in the stack, that means there is only one number in the number stack, and it's
if (optstack.Count == 0)// it's the base case:
{
//check if there is really one number in the stack:
if (numberstack.Count != 1)
{
throw new Exception("Something shouldn't happen hapepened.");
}
return(numberstack.Pop());
}
//Comfirm that there is a Operator in the stack.
char opt = optstack.Pop();
ProperFraction secondnumber = numberstack.Pop();
ProperFraction firstnumber = null;
if (numberstack.Count != 0)
{
firstnumber = numberstack.Pop();
}
ProperFraction computedresult = compute(firstnumber, secondnumber, opt);
if (computedresult == null)
{
return(null); //This is hit if the number and the operator cannot be computed.
}
numberstack.Push(computedresult);
return(evalueteStacks(numberstack, optstack));
}
public static ProperFraction evaluateSimple(IList <Object> expression)
{
Stack <ProperFraction> numstack = new Stack <ProperFraction>();
Stack <char> opstack = new Stack <char>();
//Queue q = new Queue();
//iterate through a queue of number, operator,or a sub expression.
foreach (Object ele in expression)
{
//if is number
if (ele is ProperFraction)
{
//put into numberstack.
numstack.Push(ele as ProperFraction);
}
// elseif operator
else if (ele is char)
{
if (opstack.Count == 0)// if operator stack is empty, put it in.
{
opstack.Push((char)ele);
}
else // else that stack is not empty.
{
char opt = (char)ele;
if (compare(opt, opstack.Peek()) == 1)//if it's bigger to the most recent opt in stack
{
// put it in op stack.
opstack.Push(opt);
}
else //else: it's leq to the top opt.
{
while (compare(opt, opstack.Peek()) < 1 || opstack.Count != 0)//while current op leq than top one on stack || operator stack is not empty.
{
// pop top
char topoperator = opstack.Pop();
// pop two numbers if there is no more number on top, use zero
ProperFraction secondnumber = numstack.Pop();
ProperFraction firstnumber = null;
if (numstack.Count != 0)
{
firstnumber = numstack.Pop();
}
//compute the top two number using the operator, the order matters.
ProperFraction res = compute(firstnumber, secondnumber, opt);
//put the number back to the number stack.
numstack.Push(res);
}
//put that operator in the opt stack?
opstack.Push(opt);
}
}
}
else//else it must be sub expression
{
if (!(ele is IList <Object>))// This shit if not a list
{
throw new Exception("Bad element: " + ele);
}
//Turn the sub expression into a number.
ProperFraction subexpressionnumber = evaluateSimple((IList <Object>)ele);
numstack.Push(subexpressionnumber);
}
}
// Evaluate the remaining expression empty the stack;
// return result.
ProperFraction subexpressionresult = evalueteStacks(numstack, opstack);
if (subexpressionresult == null)
{
throw new Exception("Expression or sub expression cannot be evaluated. ");
}
return(subexpressionresult);
}
