CS102 Final Exam

科目名稱：程式設計	期末考	開課系所：資工系		考試日期	2019.6.12
系所別：	年級：	學號：	姓名：	考試時間	08:30-10:30

Open book; turn off computer & mobile phone

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(10%) 請問電影《美麗人生》中，女主角 Dora 的職業是什麼？

護士
歌唱家
軍人
老師

(10%) Given the following input,

1/2
3
41/12
-9
+5/2
6.2/2
8+2
3/a
3/
3/0
+-9
x/7

If the output is
```
true
true
true
true
true
false
false
false
false
false
false
false
```
What regular expression should you fill in (2)?
// regex_match
#include <iostream>
#include <string>
#include <regex>
using std::cout;
using std::string;
using std::cin;
using std::regex;

int main()
{
    string s;
    regex re = regex("     (2)     ");
    cout << std::boolalpha;
    while (cin >> s)
        cout << regex_match(s, re) << '\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).

// regex_token_iterator
#include <iostream>
#include <string>
#include <regex>
using std::regex;
using std::sregex_token_iterator;

int main()
{
    std::string s("0AA1BB2CC3");
    regex splitter( "[0-9]+" ); // regex to split a string
    sregex_token_iterator tokenIterator( s.begin(), s.end(), splitter, -1 );
    sregex_token_iterator end; // empty iterator

    unsigned nCount = 0;
    while ( tokenIterator != end ) // tokenIterator isn't empty
    {
        ++nCount;
        std::cout << nCount << *tokenIterator << '\n';
        ++tokenIterator;
    }
    std::cout << nCount << '\n';
}
(10%) What will be the output of the following program?

// Containers vector and list
#include <iostream>
#include <vector>
#include <list>

int main()
{
    int a[10] = { 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 };
    std::vector<int> b(a, a+10);
    std::list<int> c;

    for (int i=0; i<10; ++i)
        if (b.at(i) % 5 < 3)
            c.push_back(b.at(i));
        else
            c.push_front(b.at(i));

    int n=1;
    int sum=0;
    std::list<int>::const_iterator i;
    for (i=c.begin(); i!=c.end(); ++i, n=-n)
        sum += *i * n;
    std::cout << sum << '\n';
    return 0;
}
(10%) What will be the output of the following program?

// File Stream and String Stream
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
using std::string;
using std::ifstream;
using std::ofstream;
using std::istringstream;
using std::cout;

int main()
{
    ofstream outfile("a.txt");
    outfile << "The game starts now." << '\n';
    outfile << "You have to score one thousand points.\n";
    outfile << "If you do that, ";
    outfile << "you take home a tank with a big gun.\n";
    outfile.close();

    ifstream infile("a.txt");
    string line;
    string word;
    int nLine = 0;
    int nWord = 0;
    while ( getline(infile, line) )
    {
        ++nLine;
        istringstream iss(line);
        while ( iss >> word )
            ++nWord;
    }
    cout << nLine << ' ' << nWord << '\n';

    return 0;
}
(10%) What will be the output of the following program?

// When is static objects destroyed
#include <iostream>
#include <string>
using std::cout;
using std::string;

class Object
{
public:
    Object(string s): name(s)
    { cout << name << "\tconstructed.\n"; }
    ~Object()
    { cout << name << "\tdestroyed.\n"; }
private:
    string name;
};

void f(string s)
{ Object a(s);
static Object b("Charlie");
}

int main()
{
    Object a("Alpha");
    f("Bravo");
    f("Delta");
    return 0;
}
(10%) What will be the output of the following program?

// Copy Constructor or Assignment Operator?
#include <iostream>
using std::cout;
using std::endl;
using std::ostream;

class Rational {
friend ostream& operator<<(ostream& output, const Rational& b) {
    output << b.numerator << '/' << b.denominator;
    return output;
}

public:
    Rational(int n=0, int d=1): numerator(n), denominator(d) {}
    Rational(const Rational&b) {
        numerator = b.numerator + 1;
        denominator = b.denominator;
    }
    Rational& operator=(const Rational& b) {
        numerator = b.numerator;
        denominator = b.denominator + 1;
        return *this;
    }
private:
    int numerator;
    int denominator;
};

int main()
{
    Rational a(1, 2);
    Rational b(a); // This is a copy constructor
    Rational c;
    c = b;          // This is an assignment
    Rational d = b; // Is this an assignment or a copy constructor?
    cout << a << ' ' << b << ' ' << c << ' ' << d << 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).

// vector of vector
#include <iostream>
#include <vector>
using std::vector;
using std::cout;
using std::endl;

int main()
{
    typedef vector<int> Row;
    typedef vector<Row> Matrix;
    Row r(3, 3);
    Matrix A;
    A.push_back(r);
    A.push_back(r);
    A.push_back(r);
    for (int i=0; i<3; ++i)
        for (int j=0; j<3; ++j)
            A[i][j] += 10*i + j;
    for (int i=0; i<3; ++i)
        cout << A[i].at(2) << ' ';
    cout << endl;
    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).

// Function Pointers (P.393)
#include <iostream>

int add(int a, int b)
{ return a + b; }

int sub(int a, int b)
{ return a - b; }

int mul(int a, int b)
{ return a * b; }

int divide(int a, int b)
{ return a / b; }

int main()
{
    int (*f)[](int, int) = { add, sub, mul, divide };

    for (int i=0; i<4; i++)
    {
        std::cout << f[i](12, 6) << ' ';
    }

    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; }
    int area() { return width*height; }
};

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 (4,5);
  ppoly2->set_values (4,5);
  cout << ppoly1->area() << '\n';
  cout << ppoly2->area() << '\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).
// Recursion
#include <iostream>
#include <iomanip>
using std::cout;
using std::setw;

int C(int n, int m) {
    if (n == m || m == 0)
        return 1;
    else
        return C(n-1, m) + C(n-1, m-1);
}

int main()
{
    const int K=6;
    for (int i=0; i<=K; ++i)
    {
        for (int j=0; j<=i; ++j)
            cout << setw(3) << C(i, j);
        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).

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

class Message {
private:
    string message;
    string create_mapping(string);
public:
    Message(string s): message(s) {}

    string encrypt(string s) {
        string key = create_mapping(s);
        string result;
        int k;
        for (int i=0; i<message.length(); ++i) {
            k = message[i] - 65;
            result += key[k];
        }
        return result;
    }

    string decrypt(string s) {
        string key = create_mapping(s);
        string result;
        int k;
        for (int i=0; i<message.length(); ++i) {
            k = key.find( message.at(i) );
            result += static_cast<char>(65 + k);
        }
        return result;
    }
};

int main()
{
    Message msg2("CYREYLNEUOMYROC");
    cout << msg2.decrypt("UNIVERSITY") << '\n';
    return 0;
}

string Message::create_mapping(string s)
{
    string key;
    char c;
    for (int i=0; i<s.length(); ++i)
        if (key.find( c = s.at(i) ) == string::npos)
            key += c;
    for (c='A'; c<='Z'; ++c)
        if (key.find( c ) == string::npos)
            key += c;
    return key;
}