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I am confused with a project that I study for a course. I have to build a tree-expression, I know how the algorithm works, but I have difficulties with setting up the nodes.

The instructor gave us this class: Expression Node Where it has 2 other subclasses: Constant Node and Operator Node?

and in the "Expression Tree class": Where am I building the tree-expression? I have a Stack with this type : Expression Node

my question is: after I assign an operator or an constant, how can I push it to the Stack, since the types are different.

i am working with C++ thank you.

Přemysl Šťastný
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Makaveli
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2 Answers2

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Apply polymorphism: Push pointers ( or references ) to your nodes. Since your stack contains elements of type "ExpressionNode", it can accept all types that derive from it ( Constant and Operator).

Clusty
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If you have access to boost, boost::variant is what you are looking for. See this, it is OO version of union.

header file 

#include <boost/variant.hpp>

stack<boost::variant<int,char>> s;
s.push('+');
s.push(1);
Raghavendar Reddy
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