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Class 5: Homework

You must print this sheet out and write/type answers on it!

  1. Answer given questions based on this code: 
    #include <stdio.h>

int N = 2;

int main()
{
  char fn[256];
  if (fscanf(stdin,"%s",fn) != 1)
  {
    fprintf(stderr,"No name read!\n");
    return 1;
  }

  FILE* fis = fopen(fn,"r");
  char *buff = (char*)malloc(N*sizeof(char));
  int i = 0;
  buff[i] = '\0';

  char next;
  while((next = fgetc(fis)) && next != EOF)
  {
    if (i == N-1)
    {
      N = 2*N;
      char* buffp = (char*)malloc(N*sizeof(char));
      strcpy(buffp,buff);
      free(buff);
      buff = buffp;

    }
    buff[i++] = next;
    buff[i] = '\0';
  }

  if (buff[i-1] = '\n') 
    --i;
  while(--i >= 0)
  {
    fprintf(stdout,"%c",buff[i]);
  }
  fprintf(stdout,"\n");

  return 0;
}
    		a) For each of the following, state whether the object is statically allocated, stack allocated, or heap allocated:
    1. fn
      2. 

    2. N
      3. 

    3. fn[2]
      4. 

    4. buff[2]
      5. 

    5. buffp
      6. 

    6. stdout ← HINT: you should be able to reason this out based on what you know!
      7. 

    

    
  b) What is the type of stdout?  Hint: look at fprintf's
  prototype and you should be able to figure out what its type must be!

    
    		

    
	    
    

    
	  
    2. 

	  
  2. Annotate the following code so that each * in the code
	    is labelled as either pointer declaration, pointer
	    dereference, or multiplication.

    int egcd(int u, int v, int *s, int *t)
{
  if (v == 0)
  {
    *s = 1;
    *t = 0;
    return u;
  }
  int gp, sp, tp, q, r;
  q = u/v;
  r = u%v;
  gp = egcd(v,r,&sp,&tp);
  *s = tp;
  *t = sp - tp*q;
  return gp;
}

    
	  
    3. 
	  
  3. 
	    Explain why, in the code above, the recursive call
	    egcd(v,r,&sp,&tp) has the &'s in
	    front of sp and tp.
	    
    





	    
    
	  
    4. 

	  
  4. 
	    Why is it that this code causes a program to crash

    char *name;
scanf("%s",name);

    
	    ... but this code doesn't:

    char name[20];
scanf("%s",name);






    	   

	  
    5. 




	  
  5. 
	    Fill in the blanks.  To create an array A of 20
	    doubles:
	    
    ________ A = ( ________ ) malloc( ______  * sizeof( _______ ));
	    
    
	    
    
	  
    6. 


	  
  6. 
	    Fill in the blanks.  To create an array B of 10
	    strings:
	    
    ________ B = ( ________ ) malloc( ______  * sizeof( _______ ));
	    
    
	    
    
	  
    7. 

	  
  7. 
	    Define a function div that takes to integers
	    x and y and produces their quotient (x/y) and remainder 
	    (x % b).   You should be able to call the function like
	    this:
	    
    int a,b,q,r;
scanf("%i %i",&a,&b);
div(a,b,&q,&r); ← after the call q is the quotient, r is the remainder.
	    
    
	    
    














	    
    
	  
    8.