CS102 Midterm Exam (2)

科目名稱：程式設計	第二次期中考	開課系所：資工系		考試日期	2020.4.30
系所別：	年級：	學號：	姓名：	考試時間	08:20-10:00

Open book; turn off computer & mobile phone

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(10%) Determine whether the following code has syntax errors or not. If it is correct, predict its output. If it is incorrect, point out the mistake(s).
// array and pointer
#include <iostream>
using std::cin;
using std::cout;
using std::endl;

int main()
{
    int a[3][2] = { { 11, 12 }, { 21, 22 }, { 31, 32 } };
    int* p = a[0];
    int i, j;
    for (i=0; i<3; ++i)
        for (j=0; j<2; ++j)
            *( p + 2 * i + j ) *= 2;
    for (i=0; i<3; ++i)
    {
        for (j=0; j<2; ++j)
            cout << a[i][j] << '\t';
        cout << '\n';
    }
    return 0;
}
(10%) Determine whether the following code has syntax errors or not. If it is correct, predict its output. If it is incorrect, point out the mistake(s).

// char**
#include <iostream>
using std::cout;
using std::endl;

int main()
{
    const char* a[] = { "Alpha", "Bravo", "Charlie", "Delta" };
    const char** p = a + 1;
    cout << *p << endl;
    cout << **p << endl;
    return 0;
}
(10%) Determine whether the following code has syntax errors or not. If it is correct, predict its output. If it is incorrect, point out the mistake(s).

// pass-by-reference
#include <iostream>
using std::cout;
using std::endl;

void f1(int& n)
{ cout << --n; }

void f2(int n)
{ cout << --n; }

int main()
{
    int n = 430;
    cout << --n;
    f1(n);
    f2(n);
    cout << --n << endl;

    return 0;
}
(10%) Assume the following code is compiled and run on an Intel x86 CPU. The compiler allocates 4 bytes for each integer. Please predict the output.

// reinterpret_cast
// Assume an x86 CPU and sizeof(int) == 4
#include <iostream>
using std::cout;
using std::cin;
using std::endl;

int main()
{
    int a[] = { 3, 1, 4, 1, 5, 9, 2, 6, 5 };
    int* p0 = a;
    int* p5 = &a[5];
    cout << p5 - p0 << '\t'
         << reinterpret_cast<char*>(p5) - reinterpret_cast<char*>(p0) << '\t'
         << *reinterpret_cast<char*>(p5) - *reinterpret_cast<char*>(p0)
         << endl;
    return 0;
}
(10%) What will be the output of the following program?

// cascaded function calls (P.468)
#include <iostream>
using std::cout;
using std::cin;
using std::endl;

class Rational
{
public:
    Rational(int n, int d): numerator(n), denominator(d) {};
    Rational& setNumerator(int i)   { numerator = i;   return *this; }
    Rational setDenominator(int i) { denominator = i; return *this; }
    void show() { cout << numerator << '/' << denominator << endl; }
    int numerator;
    int denominator;
};

int main()
{
    Rational a(1, 2);
    a.setNumerator(3).setDenominator(4).setDenominator(5);
    a.show();
    a.setNumerator(6).setDenominator(7).setDenominator(8);
    a.show();
    return 0;
}
(10%) What will be the output of the following program?

// Copy Constructor
#include <iostream>

class Point {
public:
    Point(int a = 4, int b = 5): x(a), y(b) {}
    Point(Point& b) { x = b.x * 2; y = b.y; }

    int x;
    int y;
};

int main()
{
    Point p1(1, 7);
    Point p2 = p1;
    Point p3(p1);
    std::cout << p2.x << p3.x << std::endl;
    return 0;
}
(10%) What will be the output of the following program?

// Overloading Assignment Operator
#include <iostream>

class Point {
public:
    Point(int a = 4, int b = 5): x(a), y(b) {}
    Point operator=(const Point& b) {
        x = b.x * 2; y = b.y;
        return *this; // Return a reference or a copy?
    }

    int x;
    int y;
};

int main()
{
    Point p1(1, 7);
    Point p2(2, 8);
    Point p3(3, 9);
    p1 = p2 = p3;
    std::cout << p1.x << p1.y << std::endl;
    (p3 = p1) = p2;
    std::cout << p3.x << p3.y << std::endl;
    return 0;
}
(10%) Determine whether the following code has syntax errors or not. If it is correct, predict its output. If it is incorrect, point out the mistake(s).

// protected
#include <iostream>
#include <string>
using std::string;
using std::cout;

class Human {
public:
    Human(string s): name(s) { cout << '+' << s; }
    ~Human() { cout << '-' << name; }
private:
    string name;
};

class Employee : public Human {
public:
    Employee(string n, string d) : Human(n) {
        department = d;
        cout << '+' << name << department;
    }
    ~Employee() { cout << '-' << name << department; }
protected:
    string department;
};

int main()
{
    Human a("A");
    Employee e("E", "F");
    return 0;
}

(10%) Determine whether the following code has syntax erros or
    not.  If it is correct, predict its output.  If it is
    incorrect, point out the
    mistake(s).

// Software Engineering Observation 12.7
#include <iostream>
#include <string>
using std::string;
using std::cout;

class String {
public:
    String(string s): txt(s) { cout << "+S" << txt; }
    ~String() { cout << "-S" << txt; }
    string txt;
};

class Human {
public:
    String name;
    Human(string s): name(s) { cout << "+H" << name.txt; }
    ~Human() { cout << "-H" << name.txt; }
};

class Employee : public Human {
public:
    Employee(string n, string d): Human(n), department(d) {
        cout << "+E" << department.txt;
    }
    ~Employee() { cout << "-E" << department.txt; }
private:
    String department;
};

void f1() {
    Human a("A");
}

void f2() {
    Employee e("E", "F");
    f1();
}

int main()
{
    Human b("B");
    Employee c("C", "D");
    cout << '\n';
    f2();
    cout << '\n';
    return 0;
}

(10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).

// Polymorphism and Virtual Functions
#include <iostream>
using std::cout;

class Polygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
};

class Rectangle: public Polygon {
  public:
    virtual int area()
      { return width*height; }
};

class Triangle: public Polygon {
  public:
    virtual int area()
      { return width*height/2; }
};

int main () {
  Rectangle rect;
  Triangle tri;
  Polygon* ppoly1 = &rect;
  Polygon* ppoly2 = &tri;
  ppoly1->set_values (4,9);
  ppoly2->set_values (4,9);
  cout << ppoly1->area() << '\n';
  cout << ppoly2->area() << '\n';
  return 0;
}

(10%) Determine whether the following code has syntax erros or
not.  If it is correct, predict its output.  If it is
incorrect, point out the
mistake(s).

// Overloading Increment Operator
#include <iostream>
using std::cout;
using std::cin;
using std::endl;

class Rational
{
public:
    Rational(int n, int d): numerator(n), denominator(d) {};
    Rational& operator++() {
        ++numerator;
        return *this;
    }
    Rational operator++(int n) {
        Rational temp(numerator, denominator);
        denominator++;
        return temp;
    }
    void show() { cout << numerator << '/' << denominator << '\t'; }
    int numerator;
    int denominator;
};

int main()
{
    Rational a(1, 2);
    Rational b(3, 4);
    (++a).show();
    b++.show();
    a.show();
    b.show();
    return 0;
}