Question

I’ve found the shunting yard algorithm, but it feels like case is a little bit different.
What if the formula your entering has variables that you want to use in another formula

you enter

cout<<"enter string"<<endl;
cin>>f;

and you enter f as

3 * (X*X) + 2*X + 7 

and you use that string and parse it to find the root, for example.

Answer 1

While it is hard to understand what you are looking for, it hints at the ability to evaluate strings as formulas. If your looking for an Eval like solution, take a look at nCalc. Stealing from their webpage:

Expression e = new Expression("2 + 3 * 5");
Debug.Assert(17 == e.Evaluate());

It also allows you to use parameters, like

e.Parameters["X"] = 10;

and then use X as part of your string to evaluate.

It let’s you convert a string representing a formula into it’s final value. If you are not asking about interpreting strings at formulas then I am at a loss for what you are asking. I recommend revising your question to better articulate the inputs and outputs of your proposed functionality.