國立暨南國際大學 105 學年度第二學期 期末考試卷

1. (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).
   
   // Range of Values (P.45)
   // Overflow (P.125)
   #include <iostream>
   using std::cout;
   using std::endl;
   
   int main()
   {
       signed short n = 32767;
       n *= 3;
       cout << n << endl;
   
       unsigned char c = 'Z';
       c = c * 4;
       cout << c << endl;
       return 0;
   }
   
   
2. (10%) What will be the output of the following program?
   // continue (P.116) vs. break (P.115)
   #include <iostream>
   
   int main()
   {
       const int K = 6;
       int count = 0;
       int i, j;
       for (i=1; i<K; i++)
       {
           if (i==5) continue;
           ++count;
       }
   
       for (j=1; j<K; j++)
       {
           if (4 == j) break;
           ++count;
       }
       std::cout << count << '\t' << i << '\t' << j << std::endl;
       return 0;
   }
   
   
3. (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 (P.196)
   #include <iostream>
   using std::cout;
   
   void swap1(int a, int b)
   {
     int temp;
     temp = a; a = b; b = temp;
   }
   
   void swap2(int* a, int* b)
   {
     int temp;
     temp = *a; *a = *b; *b = temp;
   }
   
   void swap3(int& a, int b)
   {
     int temp;
     temp = a; a = b; b = temp;
   }
   
   void print(int a, int b)
   {
       cout << a << '\t' << b << '\n';
   }
   
   int main()
   {
       int x = 6;
       int y = 20;
       swap1( x,  y); print(x, y);
       swap2(&x, &y); print(x, y);
       swap3(x, y); print(x, y);
       return 0;
   }
   
   
4. (10%) What will be the output of the following program?
   

   // Transposition Cipher - Scytale
   // The input key specifies the diameter of the scytale
   #include <iostream>
   #include <cstring>
   #include <cmath>
   using std::cout;
   using std::endl;
   
   #define MAX_WIDTH        9
   #define MAX_MESSAGE_LENGTH       200
   
   void decrypt(char* ciphertext, char* plaintext, int key);
   
   int main()
   {
       char matrix[MAX_WIDTH * MAX_WIDTH + 1];
       char plaintext[ MAX_MESSAGE_LENGTH];
   
       char ciphertext[ MAX_MESSAGE_LENGTH ] =
           "H crfaoptsrcwr eok oylmettof roeu hs";
       char *p = plaintext;
       unsigned key = 6;
   
       decrypt(ciphertext, plaintext, key);
       std::cout << plaintext << '\n';
       return 0;
   }
   
   void decrypt(char* ciphertext, char* plaintext, int height)
   {
       char* pc = plaintext;
       int i, j, offset = 0;
       int length = strlen(ciphertext);
       int width = ceil(1.0 * length / height);
   
       for (j=0; j<width; j++)
       for (i=0; i<height; i++)
           {
                   plaintext[i * width + j] = ciphertext[i + height * j] ;
           }
       plaintext[ width * height ] = '\0';
   }

5. (10%) What will be the output of the following program?
   
   // Recursive Function (P.214)
   #include <iostream>
   using std::cout;
   using std::endl;
   
   void f(int n)
   {
       if (n >= 16)
           f(n / 16);
   
       n %= 16;
       if (n < 10)
           cout << n;
       else {
           char c = 'A' + (n - 10);
           cout << c;
       }
   }
   
   int main()
   {
       f(620);
       f(65534);
       cout << endl;
       return 0;
   }
   
   
6. (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).
   
   // Accessing Class Members (P.299)
   #include <iostream>
   using std::cout;
   using std::endl;
   
   int gcd(int a, int b)
   {
       if (b == 0)
           return a;
       else
           return gcd(b, a % b);
   }
   
   class CRational
   {
       int numerator;      // 分子
       int denominator;    // 分母
   
       void Print()
       {
           this->Reduce();
           cout << numerator << '/' << denominator << endl;
       }
   
       CRational(int p = 0, int q = 1)
       {
           numerator = p; denominator = q;
       }
   
       void Reduce()
       {
           int d = gcd(numerator, denominator);
           numerator /= d;
           denominator /= d;
       }
   };
   
   int main()
   {
       CRational a(96, 72); a.Print();
       CRational b(49, 25); b.Print();
       return 0;
   }
   
   
7. (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).
   
   // Destructors and Dynamic Memory Allocation (P.326)
   #include <iostream>
   class CData
   {
       public:
           int* pdata;
   
       CData(int n=0)
       {
          pdata = new(int);
          *pdata = n;
          std::cout << "Constructor called with initial value "
               << n << std::endl;
       }
   
       ~CData()
       {
          std::cout << "Destructor called to release the memory storing "
                   << *pdata << std::endl;
          delete pdata;
       }
   };
   
   
   int main()
   {
       CData* py = new CData(2017);
       CData  m(6);
       CData* pd = new CData(20);
       delete py;
       return 0;
   }
   

8. (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).
   
   // Static data members (P.311)
   #include <iostream>
   using std::cout;
   using std::endl;
   
   class CNode
   {
   public:
       int value;
       static CNode* previous;
       CNode* pLastNode;
   
       CNode(int v) :
       value(v)
       { previous = NULL; pLastNode = this; }
   };
   
   CNode* CNode::previous = NULL;
   
   int main()
   {
       CNode a(3), b(5), c(7), d(9);
       CNode* p;
       int n = 0;
   
       for (n=0, p=d.pLastNode; p!=NULL; p=p->previous)
           n++;
       cout << n << endl;
   
       return 0;
   }
   

9. (10%) If we replace the OnDraw() function in P.669 as below, what result will be shown on the screen after you run the program?

   // CView::OnDraw()  (P.669)
   void CSketcherView::OnDraw(CDC* pDC)
   {
           CSketcherDoc* pDoc = GetDocument();
   	ASSERT_VALID(pDoc);
   	if (!pDoc)
   		return;
   
   	const float R = 200.0f;
   	const int x0 = R, y0 = R;
   	int degree;
   	float theta;
   	const CPoint origin = CPoint(x0, y0);
   	CPoint points[12];
   	for (int i=0; i<12; i++) {
   		degree = 30 * i;
   		theta = degree * M_PI / 180;
   		points[i] = CPoint(R*cos(theta), R*sin(theta));
   	}
   	pDC->MoveTo( points[0] + origin );
   	for (int i=1; i<=12; i++) {
   		pDC->LineTo( points[5*i % 12] + origin );
   	}
   }
   

10. (10%) We want to
        develop an MFC program which allows the user to input a message and
        then print out the encrypted Caesar cipher.
    
    
    However, the following code cannot be compiled successfully.  Please point out which line of the code must be revised, and how should it be revised.
    // GetWindowText()
    CString encrypt(CString s, int key)
    {
    	CString result = _T("");
    	char c;
    	for (int i=0; i<s.GetLength(); i++)
    	{
    		c =   s.GetAt(i) + key;
    		result = result + c;
    	}
    	return result;
    }
    
    void CF10View::OnBnClickedButton1()
    {
    	CString message, cipher;
    	message = GetDlgItem(IDC_TXT_MESSAGE)->GetWindowText( );
    	cipher = encrypt(message, 3);
    	GetDlgItem(IDC_TXT_CIPHER)->SetWindowText( cipher );
    }