Note: Questions 1-3 are taken from the King book, pg. 218

1. If i is a variable and p points to i, which of the following expressions
   are aliases for i?  (a and g)

   What is the meaning of each expression?

   int i = 10;

   a) *p    - 10
   b) &p    - address of p 
   c) *&p   - address of i  (dereference the address of p)
   d) &*p   - address of i (get the address of what p points to)
   e) *i    - Error 'unary *'
   f) &i    - address of i
   g) *&i   - 10
   h) &*i   - Error 'unary *'

   NOTE: In general you shouldn't have to write code that uses constructions
   like c, d, g and h since they are either erroneous or can be done in a
   more straight-forward fashion ex. can use a) instead of g)

2. If i is an int variable and p and q are pointers to int, which of the
   following assignments are legal?

   int i = 20;
   
   a) p = i; warning: assignment makes pointer from integer without a cast 
             p holds 20 or 0x14 which is not a valid address.
   b) *p = &i; warning: assignment makes integer from pointer without a cast
             the location p points to gets the value of the address of i
             i == address of i now.
   c) &p = q; Error invalid lvalue (Can't change the address of p)
   d) p = &q; warning: assignment from incompatible pointer type
              the address of q is not of type pointer-to-int
   e) p = *&q; okay - p gets the value of q.
   f) p = q;   okay and much better syntax
   g) p = *q;  p is assigned what q points to. (q was not initialized)
   h) *p = q;  warning: assignment makes integer from pointer without a cast
   i) *p = *q;


3. What are the errors in this code?

void avg_sum(double a[], int n, double *avg, double *sum)
{
    int i;
    sum = 0.0;
    for(i = 0; i < n; i++) 
        sum += a[i];
    avg = sum / n;
}


Solution:
void avg_sum(double a[], int n, double *avg, double *sum)
{
    int i;
    *sum = 0.0;
    for(i = 0; i < n; i++) 
        *sum += a[i];
    *avg = *sum / n;
}

Why would I pass in avg and sum as pointers? 
(We want to change their values, and C uses pass-by-value for function 
arguments.) 

How would I call avg_sum? 

        double x[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        double sum;
        double avg;
        avg_sum(x, 10, &avg, &sum);


Why is the following incorrect?

        double x[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        double *sum;
        double *avg;
        avg_sum(x, 10, avg, sum);

(sum and avg not initialized -- they don't point to declared double variables)


4. Our own simple implementation of strcpy:
char *
mystrcpy(char *a, char *b) 
{
  int i = 0;
  while( b[i] != '\0') {
    a[i] = b[i];
    i++;
  }
  a[i] = '\0';
  return a;
}

What kind of error checking could we do? 
(We could check if a or b are NULL, but we can't do much else.)

NOTE: We could run into problems if we call mystrcpy and the array pointed to
by b is not NULL terminated (we will keep assigning values to a until we 
eventually hit '\0' -- buffer overflow potential!)