SS2018 A5 a,b,c fix

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

class Exp {
public:
    Exp() {};

    virtual string pretty() = 0;
    virtual int eval() = 0;
    virtual Exp* simp() { return this; }
};

class IntExp : public Exp {
public:
    int val;
public:
    IntExp(int _val) {
        val = _val;
    }

    string pretty() {
        stringstream ss;
        ss << val; // Konvertierung von Integer return ss.str(); // in einen String } };
        return ss.str();
    }

    int eval() {
        return this->val;
    }
};

class PlusExp : public Exp {
public:
    Exp *e1;
    Exp *e2;
public:
    PlusExp(Exp *_e1, Exp *_e2) {
        e1 = _e1;
        e2 = _e2;
    }

    string pretty() {
        return "(" + e1->pretty() + " + " + e2->pretty() + ")"; // 1 + 2 * 3 != (1 + 2) * 3
    }

    int eval() {
        return this->e1->eval() + this->e2->eval(); //rekursion
    }

    Exp* simp() {
        //teile
        this->e1 = this->e1->simp();
        this->e2 = this->e2->simp();

        //0 + e => e
        if (this->e1->eval() == 0)
            return this->e2;
        //e + 0 => e
        if (this->e2->eval() == 0)
            return this->e1;

        return this; //nicht einfacher gemacht
    }
};

class MultExp : public Exp {
public:
    Exp *e1;
    Exp *e2;
public:
    MultExp(Exp *_e1, Exp *_e2) {
        e1 = _e1;
        e2 = _e2;
    }

    string pretty() {
        return e1->pretty() + " * " + e2->pretty(); //kp was hier der Fehler ist
    }

    int eval() {
        return this->e1->eval() * this->e2->eval();
    }

    Exp* simp() {
        //Teile vereinfachen
        this->e1 = this->e1->simp();
        this->e2 = this->e2->simp();

        //1 * e => e
        if (this->e1->eval() == 1)
            return this->e2;
        //e * 1 => e
        if (this->e2->eval() == 1)
            return this->e1;

        return this; //nicht einfacher gemacht
    }
};

int main() {
    //tests
    Exp *e = new MultExp(new PlusExp(new IntExp(1), new IntExp(2)), new IntExp(3));

    cout << e->pretty() << endl;
    cout << e->eval() << endl;
    cout << e->simp()->pretty() << endl;

    Exp *f = new MultExp(new PlusExp(new IntExp(0), e), new IntExp(1));

    cout << f->pretty() << endl;
    cout << f->eval() << endl;
    cout << f->simp()->pretty() << endl;

    return 0x0;
}