/** <summary>Returns true/false depending on whether the expession is valid or not (Respectively)</summary>
*
* <remarks>The region "SPECIFIC_CASES" detect whether an expression is a lone variable or a lone number.
* <example>"someVariable" for a lone variable, and "-10" for a lone number</example>
* Furthermore, the function also checks the following:
* <list type="bullet">
* <item><term>If the last character of the expression is an operator</term></item>
* <item><term>If the all the values in the expression list are numbers separated by spaces</term></item>
* <item><term>If the parenthesis are in the right order and properly formatted</term></item>
* </list></remarks>
*/
// ReSharper disable once CognitiveComplexity
private bool IsExpressionValid()
{
#region SPECIFIC_CASES
//Lone number case
if (CheckMethods.IsANumber(InputExpression))
{
return(true);
}
//Lone variable case
if (CheckMethods.IsAVariable(InputExpression) && ExpressionList.Count == 1)
{
return(true);
}
#endregion
//checks if the last character is an operator
if (CheckMethods.IsAValidOperator(InputExpression[^ 1].ToString()) ||
/** <summary>If the expression is valid, the method solves the expression. Otherwise, it will return null
* if the method is called and the validity of the expression is false, it will return null </summary>
*
* <remarks>The method turns the expression (which is in infix notation) into its postfix expression using the
* <see cref="ExpressionManipulation.InfixToPostfix(string[])"/> function, then solves the expression using
* a postfix expression solving algorithm described
* <a href="https://runestone.academy/runestone/books/published/pythonds/BasicDS/InfixPrefixandPostfixExpressions.html">here</a>.
* </remarks>.
*/
// ReSharper disable once CognitiveComplexity
public double?Solve()
{
if (!IsValid)
{
AnsiConsole.MarkupLine("[red]Cannot solve expression as it is invalid![/]");
return(null);
}
//If the expression is a lone number, output it back
if (CheckMethods.IsANumber(InputExpression))
{
var value = double.Parse(InputExpression);
Variables.SetAns(value.ToString());
return(value);
}
//If the expression is a lone variable, output its value back
if (CheckMethods.IsAVariable(InputExpression) && ExpressionList.Count == 1)
{
var value = Variables.GetValue(InputExpression);
if (value is not null)
{
Variables.SetAns(value.ToString());
return(value);
}
AnsiConsole.MarkupLine($"[red]The variable \"{InputExpression}\" is not initialized![/]");
return(null);
}
//Creates a copy of the list int o a string array
var tempExpressionList = new string[ExpressionList.Count];
for (var i = 0; i < ExpressionList.Count; i++)
{
tempExpressionList[i] = ExpressionList[i];
}
//substitutes the values of the variables in the expression. At this point, ALL variables are defined (checked).
//A copy is used so the expression can mamintain its variables, so the value of a variable can change if the
//vaues in its variables (if it has any) change.
for (var i = 0; i < tempExpressionList.Length; i++)
{
if (CheckMethods.IsAFunction(tempExpressionList[i]))
{
continue;
}
if (!CheckMethods.IsAVariable(tempExpressionList[i]))
{
continue;
}
tempExpressionList[i] = Variables.GetValue(tempExpressionList[i]).ToString();
}
var postfixExpression = ExpressionManipulation.InfixToPostfix(tempExpressionList);
Stack <double> operandStack = new Stack <double>();
foreach (var token in postfixExpression)
{
if (CheckMethods.IsANumber(token))
{
operandStack.Push(double.Parse(token));
continue;
}
//if it is a trigonometric function, it only needs the top of the stack. So it pops, calculates, then
//pushes again.
if (CheckMethods.IsAFunction(token))
{
operandStack.Push(Computation.Compute(operandStack.Pop(), token));
continue;
}
//if its not a number, it is an operator
var number2 = operandStack.Pop();
var number1 = operandStack.Pop();
operandStack.Push(Computation.Compute(number1, number2, token));
}
if (operandStack.Count == 1)
{
var value = operandStack.Pop();
Variables.SetAns(value.ToString()); //sets the "ans" variable to this value
return(value);
}
AnsiConsole.MarkupLine("[red]Invalid Expression (at Solve)[/]");
return(null);
}