ADT is Abstract Data Type. How can we use OOP to make ADT as primitive data structure in programming?

Three steps:

  • define a ADT class
  • overload operators
  • optimize visualization to downstream clients

Throw exception

throw exception in function will stop execution; catch exception in main function will show error message; add return 1 in exception catch will stop execution.

NOTE: Dynamic Exception (throw (const char*)) is no longer supported in C++17.

C++ Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
#include <iostream>
using namespace std;

class Rational{
public:
    // constructor
    Rational(int num = 0, int deno = 1) throw(const char*);

    // accessor and mutator
    int getNumerator();
    int getDenominator();
    void setNumerator(int num);
    void setDenominator(int deno) throw(const char*);

private:
    int _numerator;
    int _denominator;

};

Rational::Rational(int num, int deno) throw(const char*){
    if(deno == 0) {
        throw "denominator is not supposed to be zero!";
        return;
    }

    _numerator = num;
    _denominator = deno;
}

int Rational::getNumerator(){
    return _numerator;
}

int Rational::getDenominator(){
    return _denominator;
}

void Rational::setNumerator(int num) {
    _numerator = num;
}

void Rational::setDenominator(int deno) throw(const char*){
    if(deno == 0){
        throw "denominator is not supposed to be zero!";
    }
    _denominator = deno;
}

int main(int argc, char** argv){
    Rational a;
    try{
        a.setNumerator(7);
        a.setDenominator(0);
    }
    catch(const char* e) {
        cout << "Exception: " << e << endl;
        //return 1;
    }
    cout << "a = " << a.getNumerator() << '/' << a.getDenominator() << endl;
    return 0;
}

output:

1
2
Exception: denominator is not supposed to be zero!
a = 7/1

Caution: const is neccessary in try-catch structure, otherwise the error message won’t show up.

Keyword: const

Accessor(Getter): All accessor functions should be const whenever possible;
Muator(Setter): Pass input parameters by const reference possible

C++ Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
class Rational{
public:
    // constructor
    Rational(int num = 0, int deno = 1) throw(const char*);

    // accessor and mutator
    int getNumerator() const;
    int getDenominator() const;
    void setNumerator(const int num);
    void setDenominator(const int deno);

private:
    int _numerator;
    int _denominator;

};

Operator overloading

Can only create existed operations(+, -, *, /, ==, <<, >>, etc); They are non-member functions.

C++ Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
#include <iostream>
using namespace std;

class Rational{
public:
    // constructor
    Rational(int num = 0, int deno = 1) throw(const char*);

    // accessor and mutator
    int getNumerator() const;
    int getDenominator() const;
    void setNumerator(const int num);
    void setDenominator(const int deno) throw(const char*);

private:
    int _numerator;
    int _denominator;

};
// Arithmetic operators overloading
Rational operator+ (const Rational a, const Rational b);
Rational operator- (const Rational a, const Rational b);
Rational operator* (const Rational a, const Rational b);
Rational operator/ (const Rational a, const Rational b) throw(const char*);
// other operators overloading
bool operator== (const Rational a, const Rational b);


Rational::Rational(int num, int deno) throw(const char*){
    if(deno == 0) {
        throw "denominator is not supposed to be zero!";
        return;
    }

    _numerator = num;
    _denominator = deno;
}

int Rational::getNumerator() const{
    return _numerator;
}

int Rational::getDenominator() const{
    return _denominator;
}

void Rational::setNumerator(const int num) {
    _numerator = num;
}

void Rational::setDenominator(const int deno) throw(const char*){
    if(deno == 0){
        throw "denominator is not supposed to be zero!";
    }
    _denominator = deno;
}

Rational operator+ (const Rational a, const Rational b){
    Rational result = Rational(a.getNumerator()*b.getDenominator()+a.getDenominator()*b.getNumerator(),
                               a.getDenominator()*b.getDenominator());
    return result;
}

Rational operator- (const Rational a, const Rational b){
    Rational result = Rational(a.getNumerator()*b.getDenominator()-a.getDenominator()*b.getNumerator(),
                               a.getDenominator()*b.getDenominator());
    return result;
}

Rational operator* (const Rational a, const Rational b){
    Rational result = Rational(a.getNumerator()*b.getNumerator(), a.getDenominator()*b.getDenominator());
    return result;
}

Rational operator/ (const Rational a, const Rational b) throw(const char*){
    if(b.getNumerator() == 0){
        throw "The dividend cannot be zero!";
    }
    Rational result = Rational(a.getNumerator()*b.getDenominator(), a.getDenominator()*b.getNumerator());
    return result;
}

bool operator== (const Rational a, const Rational b){
    if(a.getNumerator()*b.getDenominator() == a.getDenominator()*b.getNumerator()) {
        return true;
    } else {
        return false;
    }
}

int main(int argc, char** argv){
    Rational a = Rational(1, 3);
    Rational b = Rational(2, 3);
    Rational result = a/b;

    cout << "a/b = " << result.getNumerator() << "/" << result.getDenominator() << endl;
    if(a == b) {
        cout << "same" << endl;
    } else {
        cout << "different" << endl;
    }

    return 0;
}

Output:

1
2
a/b = 3/6
different

iostream overloading and Keyword: friend

friend operator>> overloading in class public member enables operator>> to have access to the private data members

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
class Rational{
public:
    // constructor
    Rational(int num = 0, int deno = 1) throw(const char*);

    // accessor and mutator
    int getNumerator() const;
    int getDenominator() const;
    void setNumerator(const int num);
    void setDenominator(const int deno) throw(const char*);
    //Enables operator>> to have access to the private data members
    friend istream& operator>> (istream& sin, Rational& r);

private:
    int _numerator;
    int _denominator;

};
// Arithmetic operators overloading
Rational operator+ (const Rational a, const Rational b);
Rational operator- (const Rational a, const Rational b);
Rational operator* (const Rational a, const Rational b);
Rational operator/ (const Rational a, const Rational b) throw(const char*);
// other operators overloading
bool operator== (const Rational a, const Rational b);
ostream& operator<< (ostream& sout, const Rational& r);
..........

ostream& operator<< (ostream& sout, const Rational& r){
    //1. Grabbing the reference to the output stream buffer

    //2. Attach the output strings to the buffer based on my likings
    sout << r.getNumerator() << "/" << r.getDenominator();

    //3. Return the reference of the modified output stream buffer
    return sout;
}

istream& operator>> (istream& sin, Rational& r){
    //1. Grabbing the reference to the input stream buffer

    //2. Acquire the num and the denom from the input and save it to r
    char slash;
    sin >> r._numerator>> slash >> r._denominator;

    //3. Clear slash, return the reference of the modified input stream buffer
    return sin;
}

int main(int argc, char** argv){
    Rational a;
    Rational b;
    cout << "first fraction (a/b): ";
    cin >> a;
    cout << "second fraction (a/b): ";
    cin >> b;

    Rational result;
    result = a/b;
    cout << "a/b = " << result << endl;
    if(a == b) {
        cout << "same" << endl;
    } else {
        cout << "different" << endl;
    }

    return 0;
}

Output:

1
2
3
4
first fraction (a/b): 1/3
second fraction (a/b): 2/3
a/b = 3/6
different

keyword: explicit

  1. Forces the compiler to use this specific constructor to type cast
  2. Forces client to always explicit type cast. implicit type conversion is completely prohibited.

C++ Example(Wrong, can’t compile)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
class Rational{
    public:
        explicit Rational(int num = 0, int denom = 1) throw (const char*);
    ......

}

int main(int argc, char** argv){
    Rational a = Rational(2, 1);
    if(a == 3) {
        cout << "same" << endl;
    } else {
        cout << "different" << endl;
    }
    return 0;
}

C++ Example(Correct)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
class Rational{
    public:
        explicit Rational(int num = 0, int denom = 1) throw (const char*);
    ......

}

int main(int argc, char** argv){
    Rational a = Rational(3, 1);
    if(a == Rational(3)) {
        cout << "same" << endl;
    } else {
        cout << "different" << endl;
    }
    return 0;
}

Output:

1
2
a = 3/1
same

Optimize(helper function)

Add _reduce() helper functioin as a private member of the class; _reduce() means reduce fraction form

_reduce() is only be added in Rational(), setNumenator(), getDominator() and operator>>. Because other operator(+, -, *, /) will construct a Rational result automatically which will invoke Rational(). operator<< will not call Rational() but Rational() is always called before <<.

C++ Example:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
#include <iostream>
using namespace std;

class Rational{
public:
    // constructor
    explicit Rational(int num = 0, int deno = 1) throw(const char*);

    // accessor and mutator
    int getNumerator() const;
    int getDenominator() const;
    void setNumerator(const int num);
    void setDenominator(const int deno) throw(const char*);
    //Enables operator>> to have access to the private data members
    friend istream& operator>> (istream& sin, Rational& r);

private:
    int _numerator;
    int _denominator;
    void _reduce();

};
......

Rational::Rational(int num, int deno) throw(const char*){
    if(deno == 0) {
        throw "denominator is not supposed to be zero!";
        return;
    }

    _numerator = num;
    _denominator = deno;

    _reduce();
}

void Rational::_reduce() {
    int gcd = 1;
    for(int i = 1; i <= _numerator && i <= _denominator ; i++){
        if((_numerator%i == 0) && (_denominator%i == 0))
            gcd = i;
    }

    _numerator = _numerator/gcd;
    _denominator = _denominator/gcd;
}

_reduce() in function operator>> is different, because it’s a non-member function but it’s a firend function.

c++ exmple

1
2
3
4
5
6
7
8
9
10
11
istream& operator>> (istream& sin, Rational& r){
    //1. Grabbing the reference to the input stream buffer

    //2. Acquire the num and the denom from the input and save it to r
    char slash;
    sin >> r._numerator>> slash >> r._denominator;

    r._reduce();
    //3. Clear slash, return the reference of the modified input stream buffer
    return sin;
}

Because r has been saved in stack, in order to change r, we have to refer r to invoke _reduce().

Invoke _reduce() instead of r._reduce() will result in compile error, although operator>> is a friend function which have access to the private members. why?

Keyword: virtual and final

  1. virtual – permits child ADT to override the implementation of these functions; The client programmer can use the keyword override to override the base implementations
  2. final – prohibits child ADT to override these functions

C++ Example1: prohibits whole class overided

1
2
3
class Rational final {
    ......
}

C++ Example2: prohibits function overided

1
2
3
4
class Rational final {
    public:
        final getNumerator();
}

Last version of fraction ADT

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
#include <iostream>
using namespace std;

class Rational {
public:
    // constructor
    explicit Rational(int num = 0, int deno = 1) throw(const char*);

    // accessor and mutator
    int getNumerator() const;
    int getDenominator() const;
    void setNumerator(const int num);
    void setDenominator(const int deno) throw(const char*);
    //Enables operator>> to have access to the private data members
    friend istream& operator>> (istream& sin, Rational& r);

private:
    int _numerator;
    int _denominator;
    void _reduce();

};
// Arithmetic operators overloading
Rational operator+ (const Rational a, const Rational b);
Rational operator- (const Rational a, const Rational b);
Rational operator* (const Rational a, const Rational b);
Rational operator/ (const Rational a, const Rational b) throw(const char*);
// other operators overloading
bool operator== (const Rational a, const Rational b);
ostream& operator<< (ostream& sout, const Rational& r);


Rational::Rational(int num, int deno) throw(const char*){
    if(deno == 0) {
        throw "denominator is not supposed to be zero!";
        return;
    }

    _numerator = num;
    _denominator = deno;

    _reduce();
}

void Rational::_reduce() {
    int gcd = 1;
    for(int i = 1; i <= _numerator && i <= _denominator ; i++){
        if((_numerator%i == 0) && (_denominator%i == 0))
            gcd = i;
    }

    _numerator = _numerator/gcd;
    _denominator = _denominator/gcd;
}


int Rational::getNumerator() const{
    return _numerator;
}

int Rational::getDenominator() const{
    return _denominator;
}

void Rational::setNumerator(const int num) {
    _numerator = num;

    _reduce();
}

void Rational::setDenominator(const int deno) throw(const char*){
    if(deno == 0){
        throw "denominator is not supposed to be zero!";
    }
    _denominator = deno;

    _reduce();
}

Rational operator+ (const Rational a, const Rational b){
    Rational result = Rational(a.getNumerator()*b.getDenominator()+a.getDenominator()*b.getNumerator(),
            a.getDenominator()*b.getDenominator());
    return result;
}

Rational operator- (const Rational a, const Rational b){
    Rational result = Rational(a.getNumerator()*b.getDenominator()-a.getDenominator()*b.getNumerator(),
            a.getDenominator()*b.getDenominator());
    return result;
}

Rational operator* (const Rational a, const Rational b){
    Rational result = Rational(a.getNumerator()*b.getNumerator(), a.getDenominator()*b.getDenominator());
    return result;
}

Rational operator/ (const Rational a, const Rational b) throw(const char*){
    if(b.getNumerator() == 0){
        throw "The dividend cannot be zero!";
    }
    Rational result = Rational(a.getNumerator()*b.getDenominator(), a.getDenominator()*b.getNumerator());
    return result;
}

bool operator== (const Rational a, const Rational b){
    if(a.getNumerator()*b.getDenominator() == a.getDenominator()*b.getNumerator()) {
        return true;
    } else {
        return false;
    }
}

ostream& operator<< (ostream& sout, const Rational& r){
    //1. Grabbing the reference to the output stream buffer

    //2. Attach the output strings to the buffer based on my likings
    sout << r.getNumerator() << "/" << r.getDenominator();

    //3. Return the reference of the modified output stream buffer
    return sout;
}

istream& operator>> (istream& sin, Rational& r){
    //1. Grabbing the reference to the input stream buffer

    //2. Acquire the num and the denom from the input and save it to r
    char slash;
    sin >> r._numerator>> slash >> r._denominator;

    r._reduce();
    //3. Clear slash, return the reference of the modified input stream buffer
    return sin;
}

int main(int argc, char** argv){
    Rational a;
    Rational b;
    cout << "first fraction (a/b): ";
    cin >> a;
    cout << "second fraction (a/b): ";
    cin >> b;
    cout << "new a = " << a << endl;

    Rational result;
    result = a/b;
    cout << "a/b = " << result << endl;
    cout << "a = " << a << endl;
    if(a == Rational(3)) {
        cout << "same" << endl;
    } else {
        cout << "different" << endl;
    }

    return 0;
}

Reference material:
Book: Thinking in C++, Volume 1, 2nd Edition, Bruce Eckel.
Lectures: University of Waterloo, CS 247 (Software Abstraction and Specificati), 2020 spring term, professor Scott Chen.