Department of Computer Science

University of Illinois at Urbana-Champaign

Computer Science 101: Mid Term Exam II (60 minutes)

 


Name:                                                                         NetID:
 

Lab Section:                                                               Date: November 1, 2007

 


No questions will be answered during this examination.  If you do not understand a question, read it again.  If you still do not understand it, make reasonable assumptions and write them down. (Points will be deducted if unreasonable assumptions are made.)

DO NOT CHEAT: Cheating includes not only copying from another person but also allowing someone to copy from you.  Anyone who copies or allows someone to copy will receive a score of zero.  So be defensive and protect your work.

This examination contains 11 pages including this page. Check that your copy is complete, and ask for a replacement if it is not. Do all your work on these pages. For your own protection, in case pages come apart, write your NetID at the TOP of each page before beginning work.

The number of points for a question is roughly proportional to the amount of time you may need for it. Don’t spend too much time on any one question.

Do not forget to sign the attendance list. If your exam is misplaced and you did not sign the attendance list then you will receive a zero score for the exam.

You may not use any electronic devices, book, notes or other references during this examination.

DO NOT WRITE IN THIS SPACE

Section

Possible Score

Deduction

Grader

1

6

 

 

2

5

 

 

3

5

 

 

4

5

 

 

5

8

 

 

6

8

 

 

7

5

 

 

8

7

 

 

9

6

 

 

10

6

 

 

11

8

 

 

12

10

 

 

13

6

 

 

14

14

 

 

15

14

 

 

16

12

 

 

Total

125

 

 

 

 

Exam Scoreà

 

A

 

 

 

1.      Answer the following questions by filling in the blanks.

 

a) When you use the Unix ls command to list the contents of a directory the output may not fit on one full terminal screen. Since the screen scrolls you may not see the first part of the output. Fill in the blank line to solve this problem:

 

  ls  -la __|____ more

 

b) Fill in the blank to send the output from the ls command to the file “screen.txt”. 

 

ls -la __>____ screen.txt


 

2.      Assume that you are in your home directory which contains the file lab9.c Write Unix commands to create a subdirectory named lab9 and next, without changing directories, copy the file named lab9.c located in your home directory into the lab9 directory (do not copy any other files).

            _________mkdir lab9___________________________________________________

 

 

            _________cp  lab9.c  lab9 ___________________________________________________


                       

3.      The following program is saved in a file named test.c, 

 

#include  <stdio.h>

#include  <math.h>

 

void main(void)

{
     double x;

     printf("Enter a number:");

     scanf("%lf", &x);

     printf("sin(%lf) = %lf \n",x, sin(x));

  }

 

Write a single command to compile the code in the file test.c, so that to run your program at the Unix prompt you would type:
testing
instead of a.out.

 

 

______gcc  test.c  –lm  -o testing_______________________________

 

 

4.      Write a single Unix command to move the files named file1, file2, file3 located in your current directory into a subdirectory named dirname. You may assume that these three files are the only files located in your current directory and that dirname already exists.

 

______mv  file1  file2  file3  dirname___OR ____________mv  *  dirname _____________

5.      Which of the following code fragments assign the value 10 to each element of the array named Array ?  Circle each correct answer. There may be more than one correct answer.

 

 

a)  

int Array[10][10];

int i,j;

for(i=0; i<10 ;i++)

for(j=0; j<10 ;j++)

     Array[j][i] = 10;

 

 

b)  

int Array[10][10] = {10};


c)
int Array[10][10];

strcpy(Array,10);

 

 

d)      

int Array[10][10];
int i,j;

for(i=0; i<10 ; i++)

{
     Array[0][i] = 10;

for(j=1; j<10 ; j++)

     Array[j][i] = Array[j-1][i];

}

 

 

6.      The following program compiles and runs without errors. Write the output of this program.

 

 

#include <stdio.h>

 

void main(void)
{

 

   printf("%i ", 3/4);

 

   printf("%i ", 3%4);

 

   printf("%i ",3/4*4);

 

   printf("%i ",3+3*3);

 

}



_______0                3                      0                      12______________

7.      The following program compiles and runs without errors. Write the output of this program:

#include <stdio.h>

 

void main(void)

{

     int Array[3], Xarray[] = {1 , 2 , 3};

int i;

for(i=0 ; i<3 ; ++i)

{

Array[i] = i;
printf("%i ", Array[i]);

 

}

for(i=0 ; i<3 ; ++i)

printf("%i ", Xarray[i++]);

  }

 

 

 

 

_______0                      1                      2                      1                      3_____________

 

 

 

8.      There is an error on three different lines of code in the following program. Write the corrected lines in the blanks provided.  Only three lines need be rewritten. There is one syntax error, one run time error and one logical error.

The program below should read 3 integers, compute and display the average of the 3 integers.
For example, if the 3 integers were 2, 3 and 5 then the program would print the average as 3.33.

#include <stdio.h>

 

void main(void)

{
     int i, sum=0;               _____________________________

     int Array(3);                _____[3];____________________ (only change shown)

 

for(i=0 ; i< 3 ; ++i)        _____________________________

  scanf("%i", Array[i]);          ____&Array[i]__________ (only change shown)

 

for(i=0 ; i< 3 ; ++i)        _____________________________

 

 sum += Array[i];       ________sum/3.0__OR (float)sum/3_OR variations__ (only change shown)

printf("%.2f \n",sum/3);     _____________________________

   }

 

 

9.      The following C program compiles and runs without errors.

Write the output of this program when it is executed.

#include <stdio.h>

 

void main(void)

{

  int i = 1, n = 3, sum1 = 0, sum2 = 0,sum3 = 0;

  while(i <= n)

  {

     sum1 = sum1 + i;

     i = i + 1;

  }

  printf("%i %i \n",i,sum1);  


  for(i = 1; i <= n; i = i+1)

     sum2 = sum2 + i;

  printf("%i %i \n",i,sum2);

 

  i = 5;
  do{

     sum3 = sum3 + i;

     i = i + 1;   

  }while(i <= n);

  printf("%i %i \n",i,sum3);

}

 

 

 

___________4            6__________________________________________________________

 

 

___________4            6__________________________________________________________

 

 

___________6            5__________________________________________________________

 

 

10.  The following C program compiles and runs without errors.
Write the output of this program when it is executed.

#include <stdio.h>

void main(void)

{

     int x = 5, y = 5;

     do

x = x + x;

     while(x < 5);

     while(y < 5)

          y = y + y;

     printf("%i %i \n", x , y);

  }

 

 _________10  5_______________________________________________

 

 

11.  Assume we have written a function named  my_prod  as defined below:

 

int my_prod(int x, int y)

{

return x + y;

}

 

Circle each of the following that are valid prototypes of the function  my_prod. There may

be more than one correct answer.

 

a) void my_prod(int x, int y)



b) int my_prod(int a, int b);



c) int my_prod(int x, int y) { return x + y };



d) int my_prod(int x, int y);

12.  The following C program compiles and runs without errors.

Write the output of this program when it is executed.

      #include <stdio.h>

#include <string.h>

void main(void)
{
   char password[32] = "CS101";
   char course[32] = {'C','S','1','\0','5'};
   printf("%s \n", password);
   printf("%s \n", course);
   printf("%c \n",password[1]);
   strcpy(password, course);
   printf("%s \n", password);
   if (strcmp( password, "CS101") == 0)
      printf("A \n");
   else
      printf("B \n");
}

 

 



            _______CS101______________________________________

 

 


 

            _______CS1______________________________________

 

 


 

            _______S_______________________________________

 

 



            _______CS1______________________________________

 

 


 

            ______B________________________________________

 

 

 

 

 

 

13.  The following C program compiles and runs without errors.

Write the output of this program when it is executed.


#include <stdio.h>

 

void set_elements(int x, double list[])

{

  list[0] = x;

  x = 3*x;

  list[1] = x;

}

 

void main(void)

{

  double price[2] = {7.0, 9.0};

  int x = 2;

  set_elements(2, price);

  printf("x = %i \n", x);

  printf("price[0]=%.2lf \n", price[0]);

  printf("price[1]=%.2lf \n", price[1]);

}

 

 

 

 

_________x =2____________________________________________




_________price[0] = 2.00____________________________________________




_________price[1] = 6.00____________________________________________

 

 

 

 

 

 

 

 

 

 

14.  Complete the code for the function named replace_max by filling in the blanks below. This   function finds and replaces each occurrence of the maximum value of an array named list with a given number, x. The function has three input arguments: the actual array, the number of elements in the array, and the given value for replacement. The function does not return a value. You may assume that list is non-empty. To see how the function replace_max should work consider the following example:

 

#include <stdio.h>

void replace_max( int list[], int count, int x);

 

void main(void)

{

 int i , total , list[4] = {3 , -2 , 1 , 3};

 replace_max( list , 4 , -1 );

 for(i=0; i<4 ; i=i+1)

      printf(" %i ", list[i]);

 printf("\n");

}

displays the values:

 -1   -2   1   -1

however your code should enable replace_max to work for any non-empty array of integers.

___void________ replace_max( int list[], int count, int x)

{

     int max, i , total = 0;

     /* initialize max */   

 

     max = ___list[0]_________________________ ;

 

     /* find maximum value of the array and assign to max */

          for(i = 0; i<count ; ++i)

          if ( __list[i] > max_____ )

                    max = ____list[i]__________ ;

     /* replace the elements of array equal to max with x */

          for(i = 0; i<count ; ++i)

          if ( ____max == list[i]_____ )

                    _____list[i]_____ = _x____ ;

}

15.  Convert the flowchart shown below to C code by writing a switch statement. You should NOT    

 use any  if , if-else or nested ifs in your code. You may assume that choice is an integer     

 variable. Hint: you may need to use the break statement.

 

 

 

 

 

 

 

 

                                    switch(choice)

                                    {

                                                case 1: N = 16;

                                                            break;

                                                case 2: N =128;

                                                            break;

                                                case 3: N = 1024;

                                                            break;

                                                default: N = -1;

                                                             break;  /* the last break is always optional */

                                    }

 

 

 

 

 

 

 

 

 

 

 

 

 

16.  Write a complete function named  dist_to_origin. This function has two input parameters  x and y, both of datatype double. The function dist_to_origin returns the value  .

For example, to compute the distance to the orgin for the point (3.0 , 4.0) you would call your function as follows:

 

#include <stdio.h>

#include <math.h>

double dist_to_origin( double x, double y);

 

void main(void)

{

printf("%lf \n", dist_to_origin(3.0,4.0));

}

Which would display the result:

 5.000000

      Of course your code should work correctly for any point and not just (3.0,4.0). Write your code for the function dist_to_origin below. Hint: You may want to use the sqrt function. Do NOT write the code for main. Do NOT include comments in your code.

 

 

double   dist_to_origin( double x , double y)

{

            return sqrt( x*x + y*y );

}