Midterm Exam (3)
Introduction to Computer Science
NCNU CSIE

Date: December 29th, 2010
Time: 14:10-16:00
Open book; turn off computer & mobile phone

1. (10%) What will be the output of the following program?

   #include <iostream>
   int main() // Understanding bitwise operators.
   {
         unsigned s = 1229;
   
         int i = (s >> 5) & ~(~0 << 4);
         std::cout << i << std::endl;
   }

2. (10%) What will be the output of the following program?
   
   #include <iostream>
   using std::cout;
   using std::endl;
   
   int main()
   { 
       int m=25, n=13;
       m -= n += 2;
       cout << m << ' ' << n << endl;
       return 0;
   }
   

3. (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).

   #include <iostream>     // Reference to a variable
   using std::cout;
   using std::endl;
   
   int main()
   {
       int value = 12;
       int& rvalue = &value;
        value += 29;
       cout << value + rvalue << endl;
   }
   
   

4. (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).

   // Checksum
   #include <iostream>
   using std::cout;
   using std::endl;
   
   int main()
   { int cksum;
     char *p;
     char buf[8192] = "December";
   
           /*
            * Draft 8 POSIX 1003.2:
            *
            *   s = sum of all bytes
            *   r = s % 2^16 + (s % 2^32) / 2^16
            *   cksum = (r % 2^16) + r / 2^16
            */
   
     cksum = 0;
     for (p = buf; *p; ++p)
           cksum += *p; 
   
     cksum = (cksum & 0xffff) + (cksum >> 16);
     cksum = (cksum & 0xffff) + (cksum >> 16);
     cout << cksum << endl;
     return (0);
   }

   
   

5. (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).

   // Array
   #include <iostream>
   using std::cout;
   using std::endl;
   
   int main() 
   {
       int value[10] = { 1, 3, 5, 7, 9};
       int sum = 0;
   
       for (int i=0; i<10; i += 2)
           value[i] = i;
       for (int i=0; i<10; i++)
           sum += value[i];
       cout << sum << 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).
   
   // break vs. continue
   #include <iostream>
   using std::cout;
   using std::endl;
   
   int main()
   { 
       int sum=0, i = 1;
       for (i=1; i<10; i++)
           if (i++ == 5) break;
           sum += i++;
       cout << i << '\t' << sum << endl;
       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).
   
   // String pointers vs. string arrays.
   #include <iostream>
   
   using std::cout;
   using std::endl;
   
   int main()
   {
       char str[10] = "December";
       char* p = str;
       cout << str << endl;
       cout << p++ << endl;
       for ( ; *p != '\0'; p++)
           *p ^= 0x20;
       cout << p << endl;
       cout << str << endl;
   }

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).

   #include <iostream>
   using std::cout;
   using std::endl;
   
   // Function to eliminate spaces from a string
   void eatspaces(char* str)
   {
      int i(0);                              // 'Copy to' index to string
      int j(0);                              // 'Copy from' index to string
   
      while((*(str + i) = *(str + j++)) != '\0')  // Loop while character
                                                  // copied is not \0
         if(*(str + i) != ' ')                    // Increment i as long as
            i++;                                  // character is not a space
      return;
   }
   
   int main()
   {
       char expr[] = "2 + 38-5";
   	eatspaces(expr);
   	cout << expr[3] << expr[7] << endl;
       return 0;
   }
   
   

9. Check whether the following program has any mistake. If yes, point out the mistakes and correct them; if no, predict the output of the program.
   

   #include <iostream>
   using std::cout;
   
   int sum(int arg1, int arg2, int arg3 = 30, int arg4 = 40);
   
   int main()
   {
           cout << sum(5, 5,  , 5) << "\n";
           return 0;
   }
   
   int sum(int arg1, int arg2, int arg3, int arg4)
   {
           return arg1 + arg2 + arg3 + arg4;
   }

10. Check whether the following program has any mistake. If yes, point out the mistakes and correct them; if no, predict the output of the program.
    

    #include <iostream>
    using std::cout;
    
    int sum(int a, int b);
    int diff(int a, int b);
    int product(int a, int b);
    
    int main()
    {
    	int (*pfun[3])(int, int) = {sum, diff, product};
        cout << pfun[1]( (*pfun)(12, 2), (*(pfun+2))(9, 2) ) << std::endl;
        return 0;
    }
    
    int sum(int arg1, int arg2)
    { return arg1 + arg2; }
    
    int diff(int arg1, int arg2)
    { return arg1 - arg2; }
    
    int product(int arg1, int arg2)
    { return arg1 * arg2; }