1. Check all correct answers.

(a) Suppose Test1 and Test2 are two subdirectories of the same parent directory. There is file myprog.c in the directory Test1. Your current working directory is Test2and you want to save a copy of the existing file under the name prog2.c. Which command will do it?
      Correct answer:     cp ../Test1/myprog.c prog2.c
(The answer mv ../Test1/myprog.c ./prog2.c was less wrong than other incorrect answers (1 mark out of 5). With this command, the user would obtain the desired file in current directory, but the file myprog.c in directory Test1 would be erased.)

(b) If variables int n and double x are declared in the program, then the assignment x=n is

• safe and sound (4 out of 5);
• will pass compilation but may lead to a mathematical error due to roundoff effect (0 out of 5);
• Correct answer: will cause no problems for the program, but isn't best in terms of style; better use the explicit cast: x=(double)n;

(c) What is, technically, the word main at the beginning of every C program?
      Correct answer: A reserved name of function recognized by the operating system, which initiates execution of this function.

(d) Which sentence best describes the following tiny program?

   int main()
   {
     while(5){ return(0);}
   }  

• Correct answer: The program will stop instantly without printing anything. (Try to run the debugging version.)
• The loop condition is always true and the program will never stop. (1 out of 5): The first part of argument is correct, but as the program enters the loop, the return statement forces immediate stop. Everything else, other than return, would cause infinite loop.
• The program will return value 0 five times. (This doesn't make sense at all: 5 is not a loop counter and the program cannot stop more than once.)
• return(0) is misplaced; however the program will pass compilation. (1 out of 5): Usually, the return statement is placed at the end of program, after all loop braces and braces of if-else constructions are closed. However, it is not a mistake to terminate a program as it is done here. (Provided the programmer achieves a desired effect.)
• The compiler will report a syntax error. (Simply wrong)

2. Programming question: see Lab 8.

3. Trace question. Here is the required table (Only values that are assigned new values or checked in conditions at current step are shown).

 Line |   i  |   j   |   k   |  cond. |  Output
 -----------------------------------------------
 1    |   ?  |   1   |   ?   |        |    
 2    |   1  |       |       | (1<5) T|    
 4    |   1  |       |       | (1<3) T|    
 6    |      |       |20+1=21|        |    
 7->16|      |       |       |        | 21 
 17->2|   2  |       |       | (2<5) T|    
 4    |   2  |       |       | (2<3) T|    
 6    |      |       |20+0=20|        |    
 7->16|      |       |       |        | 21 
 17->2|   3  |       |       | (3<5) T|    
 4    |   3  |       |       | (3<3) F|    
 8->10|      |   1   |       | (1==0)F|    
 12->13      |       |       |        | -- 
 14   |      | (!1)=0|       |        |    
 16   |      |       |  20   |        | 20
 17->2|   4  |       |       | (4<5) T|  
 4    |   4  |       |       | (4<3) F|  
 8->10|      |   0   |       | (0==0)T|  
 11   |      |       |   0   |        |  
 14   |      | (!0)=1|       |        |  
 16   |      |       |   0   |        |  0
 17->2|   5  |       |       | (5<5) F|   
 2->18|   5  |       |       |        |  5

4. By taking sample nonnegative value(s) of x and tracing the code guess the purpose of the following function:

10  void f(int x)
11  {
12    while (x)
13    {
14      printf("%d", x%10);
15      x=x/10;
16    }
17  }

 Line  |  x  | cond  |  Output
 -----------------------------
 10    | 735 |       |  	
 12    | 735 |  T    |  	
 14    | 735 |       |   5	
 15    | 73  |       |  	
 16->12| 73  |  T    |  	
 14    | 73  |       |   3	
 15    | 7   |       |  	
 16->12| 7   |  T    |  	
 14    | 7   |       |   7	
 15    | 0   |       |  	
 16->12| 0   |  F    |  	
 17    |       return    

Here is a program that includes this function. You can check how everything works in practice.

6. Given program with errors;     corrected program.