Mid-Term Exam (1)
Introduction to Computer Science
NCNU CSIE

Date: October 26th, 2011
Time: 14:10-16:00
Open book; turn off computer & mobile phone

1. What will be the output of the following program?

   #include <iostream>
   int main() // Understanding bitwise operators.
   {
         unsigned s = 1026;
   
         int i = (s >> 3) & ~(~0 << 3);
         std::cout << i << std::endl;
         return 0;
   }
   
   

2. What will be the output of the following program?
   
   #include <iostream>
   int main()
   {
       char s[] = "WLAN";
       for (int i=0; i<4; i++)
           s[i] &= 0xF9;
       std::cout << s << std::endl;
       return 0;
   }
   
   
   
3. What will be the output of the following program?
   
   #include <iostream>
   int main()
   {
       int a[] = { 1, 2, 3, 4, 5 };
       for (int i=0; i<5; i++)
           a[++i] *= 2;
       for (int i=0; i<5; i++)
           std::cout << a[i];
       std::cout << std::endl;
       return 0;
   }
   
   
4. What will be the output of the following program?
   
   #include <iostream>
   int main()
   {
       signed char a(3);
       for (int i=0; i<3; ++i)
           a = 4*a + 3;
       std::cout << static_cast<signed int>(a) << std::endl;
       return 0;
   }
   
   
5. Consider the following binary representation of a signed short integer (stored in two's complement).  Convert it to a decimal number.

   10000001 10000001

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).
   
   // dec2bin.cpp
   #include <iostream>
   using std::endl;
   using std::cout;
   
   int main()
   {
       short i;
       short b[8] = { 26 } ;
       for (i=0; i<7; i++)
       {
           b[i+1] = b[i] / 2;
           b[i] %= 2;
       }
   
       for (i=7; i>=0; i--)
          switch (i)
          {
               case 0:
                  cout << '0';
                  break;
               case 1:
                  cout << '1';
                  break;
           }
       cout << 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).

   #include <iostream>
   using std::cout;
   using std::endl;
   
   int main()
   {
       const int N = 3;
       int a[N][N] = { { 1, 2, 3 }, { 2, 2, 3 }, { 3, 2, 3 } };
       int at[N][N];
       int c[N][N] = { 0 };
       int i, j, k;
       for (i=0; i<N; i++)
           for (j=0; j<N; j++)
               at[i][j] = a[j][i];
       for (i=0; i<N; i++)
           for (j=0; j<N; j++)
               for (k=0; k<N; k++)
                   c[i][j] += a[i][k] * at[k][j];
       for (i=0; i<N; i++)
       {
           for (j=0; j<N; j++)
               cout << c[i][j];
           cout << endl;
       }
       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).

   #include <iostream>
   int main()	// break in a nested loop
   {
       for (int i = 1; i < 6; i++) 
   	for (int j = 1; j < 6; j++)
   	{
   		if (j==4)
   			break;
   		std::cout << i << std::endl;
   	}
   }
   

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.
   

   // exchange_sort.cpp 
   #include <iostream>
   #include <iomanip>
   using std::cin;
   using std::cout;
   using std::endl;
   using std::setw;
   
   int main()
   {
   	const int MAX = 4;
   	int data[MAX] = { 1, 0, 2, 6};
   	int i, j, temp;
   
   	for (j=0; j<=MAX-2; j++)
   	{
   		for (i=j+1; i<=MAX-1; i++)
   		{
   			if (data[j] > data[i])
   			{
   				temp = data[j]; data[j]=data[i]; data[i]=temp;
   			}
   		}
           	if (j == 1)
   		{
   		    cout << endl << "Round " << j+1 << ":\t";
   		    for (i=0; i<MAX; i++)
   			cout << data[i] << '\t';
   		}
   	}
           return 0;
   }

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.
    

    // break vs. continue
    #include <iostream>
    using std::cout;
    using std::endl;
    
    int main()
    { 
        int sum=0, i = 1;
        do {
            if (i++ == 6) continue;
            sum += i++;
        } while (i<10);
        cout << i << '\t' << sum << endl;
        return 0;
    }