// given a left and right side of an equation, a Steps object, and if the unknown is time (for special cases)
public static void solveEquation(bool isTime, Steps showYourWork, Expression l, Expression r, int unknownQuantityIndex)
{
//write down current step of equation
showYourWork.AddStep(l.ToString() + " = " + r.ToString());
//if the unknown is on the right side, then flip them
Expression rightSide = null;
Expression leftSide = null;
if (l.GetIsKnown())
{
// leftSide is known, rightSide is NOT known
leftSide = r;
rightSide = l;
}
else if (r.GetIsKnown())
{
// leftSide is unknown, right is (leave the equation as is)
leftSide = l;
rightSide = r;
}
else
{
//if there are variables on both sides, then something went wrong
throw new System.ArgumentException("ERROR: Both sides of equation contain an unknown value");
}
//add step to work
showYourWork.AddStep(leftSide + " = " + rightSide.Evaluate());
//essentially does algebra until the variable is isolated on one side
while (leftSide is BinaryExpression)
{
BinaryExpression binaryLeftSide = (BinaryExpression)leftSide;
char expressionOperator = binaryLeftSide.GetOperator();
bool isOperand1Known;
Expression knownExpression;
// change the left side by taking the unknown branch and isolating it
if (binaryLeftSide.GetOperand1().GetIsKnown())
{
knownExpression = binaryLeftSide.GetOperand1();
isOperand1Known = true;
leftSide = ((BinaryExpression)leftSide).GetOperand2();
}
else if (binaryLeftSide.GetOperand2().GetIsKnown())
{
knownExpression = binaryLeftSide.GetOperand2();
isOperand1Known = false;
leftSide = ((BinaryExpression)leftSide).GetOperand1();
}
else
{
throw new System.ArgumentException("ERROR: Neither expression in the leftside contains a known value");
}
// Change right side in accordance with what was removed from the left side
if (expressionOperator == '+')
{
rightSide = new BinaryExpression(rightSide, knownExpression, '-');
}
else if (expressionOperator == '-')
{
if (isOperand1Known)
{
rightSide = new BinaryExpression(knownExpression, rightSide, '-');
}
else
{
rightSide = new BinaryExpression(rightSide, knownExpression, '+');
}
}
else if (expressionOperator == '*')
{
rightSide = new BinaryExpression(rightSide, knownExpression, '/');
}
else if (expressionOperator == '/')
{
if (isOperand1Known)
{
rightSide = new BinaryExpression(knownExpression, rightSide, '/');
}
else
{
rightSide = new BinaryExpression(rightSide, knownExpression, '*');
}
}
else if (expressionOperator == '^' && !isOperand1Known)
{
float exponent = Mathf.Pow(knownExpression.Evaluate(), -1);
UnaryExpression exponentExpression = new UnaryExpression(exponent.ToString());
rightSide = new BinaryExpression(rightSide, exponentExpression, '^');
}
else
{
throw new System.ArgumentException("ERROR: Invalid operator " + expressionOperator);
}
showYourWork.AddStep(leftSide + " = " + rightSide.Evaluate());
showYourWork.SetAnswer(rightSide.Evaluate());
}
//If we are solving for time, the answer cannot be negative
if (rightSide.Evaluate() < 0 && isTime)
{
throw new System.ArgumentException("ERROR: Time cannot be negative");
}
showYourWork.ReplaceLastValue(leftSide + " = " + rightSide.Evaluate() + " " + standardUnits[unknownQuantityIndex]);
}
