eTreeFile

#include<iostream>
#include<string>
#include <stack>
using namespace std;

struct node{
    char info;
    node* left;
    node* right;
};



//Determines the priority of an operator
int priority(char op){
//  if ((op =='('))
    //  return 0;
    if ((op =='+') || (op =='-'))
        return 1;
    else if ((op =='/') || (op =='*'))
            return 2;
    else return -1;
}

//Places a char from the input stack into a new treenode
node* makeNode(char info){
    node* childnode;
    childnode = new node;
    childnode->info = info;
    childnode->left = NULL;
    childnode->right = NULL;
    return childnode;
}


//Using a recursive function, the value of the expression is Calculated
int evaluateTree(node* treenode){
    int x,y,z;
    if ((treenode->info) == '+'||(treenode->info) == '-'||(treenode->info) == '*'||(treenode->info) == '/') {
        x = evaluateTree(treenode->left);
        y = evaluateTree(treenode->right);
        if (treenode->info=='+')
            z=x+y;
        else if (treenode->info=='-')
            z=x-y;
        else if (treenode->info=='*')
            z=x*y;
        else if (treenode->info=='/')
            z=x/y;
        return z;
    }
    else return treenode->info - '0';
}
bool isdigit(char temp)
{
    return temp <'9' && temp >'0';
}


void infixTopostfix(string infix, string &postfix)
{ int j = 0;
  stack <char> charStack;
  char temp;
    for(int i = 0; i < infix.length(); i++)
    {   temp = infix[i];
        if (isdigit(temp))
                postfix += temp;
        else if (temp == '(')
               charStack.push(temp);
        else if (temp == '+'||temp == '-'||temp == '*'||temp == '/')
                    { while( !charStack.empty() && (priority(temp) <= priority(charStack.top())))
                                { char c = charStack.top();
                                    charStack.pop();
                                    postfix += c;
                                 }
                                charStack.push(temp);
                    }

            else if (temp == ')')
                    { while(! charStack.empty() && charStack.top() != '(')
                                { char c = charStack.top();
                                    charStack.pop();
                                    postfix += c;
                                 }
                        charStack.pop();
                    }
    }
    while( ! charStack.empty() )
        { char c = charStack.top();
            charStack.pop();
            postfix += c;
         }
}

int main(){
    stack<node*> treenodes;  // stack for output node pointer addresses
    char temp, ch, again=' ';
    string infix, postfix; // the infix expression read from the line
    while (again != 'n')
    {   postfix=""; // the infix expression read from the line
        cout << "Please enter an Infix Expression" << endl;
        cin >> infix;
        infixTopostfix(infix, postfix);
        for(int i =0; i<postfix.length();i++)
        {   temp=postfix[i];
            //If it is operand, make it into a node, add push it
            if (isdigit(temp))
                treenodes.push(makeNode(temp));
            if ((temp=='+') || (temp=='/') || (temp =='-') || (temp=='*'))
               { node *t,*t1, *t2;
                 t2 = treenodes.top(); treenodes.pop();
                 t1 = treenodes.top(); treenodes.pop();
                 t = makeNode(temp);
                 t->right = t2;
                 t->left = t1;
                 treenodes.push(t);
                }
        }

        node *Tree  = treenodes.top(); treenodes.pop();

        cout << "Would  you like to evaluate the expression? (y/n)";
        cin >> ch;
        if (ch == 'y' || ch == 'Y')
        {
            int answer = evaluateTree(Tree);
            cout << endl << "Evaluation: " << answer << endl;
        }

        cout << endl;
        cout << "Would  you like to convert another expression? (y/n)";
        cin >> again;

    }
}