C++ Help

Jeice

int array[10];

for (int i =1; i <= 10; i ++)
      array[i] = i;
 

There's suppose to be something wrong with the above code. I figure it's because the array has 10 slots, but the first slot starts at 0, so the correct code should be:

int array[10];

for (int i =0; i < 10; i ++)
      array[i] = i+1;

Is that right?


2) We have the following variables in the following addresses

p is at address 100012
q is at address 100008
r is at address 100004
s is at address 100000


and then we have

int p = 100;
int q = 200;
int *r = 0;
int **s = 0;

r = &p;
s = &r;

/* what do the following print?

print (r)
print (*r)
print (s)
print (*s)
print (**s)

*/

What I got is

r prints 10012
*r prints 100
s prints 10004
*s prints 10012
**s prints 100

is this right? Can someone please help me visualize it with a diagram. The diagram I draw is this, but I don't know what r is pointing to, or what s is pointing to. I'm getting confused with the int **s = 0.

r [] at address 10004                  p [100] at address 10012

s [] at address 10000                 q [200] at adress 10008

I also have the following diagram, can someone help put it into code

pointer to int                                      int

p1 [100] at address 50  --------------> x [5] at address 100
p2 [200] at address 60 ---------------> y[7] at address 200
p3 [0] at address 70                           null pointer

My solution

int x = 5
int y = 7

int *p1 = &x;
int *p2 = &y;
int *p3 = 0

Chanus

For 1, yes... if it's <= 10 then you will overrun the bounds of your array.

<< Edit: Is "array = i+1;" placing the value of i in your array so that it will read 1, 2, 3, 4, 5... 10? because that's what it will do..


For 2... I dunno.

admanb

You have it right (except your values for r, s, and *s are missing a 0). Here's how I would describe it.

100012 p = 100
100008 q = 200
100004 r = 100012
100000 s = 100004

* notation is confusing, because it means two different things in two different contexts.

In a declaration, it declares the type of a variable to be a pointer. Example:

int p; //p is an integer
int *p; //p is a pointer to an integer
int **p; //p is a pointer to a pointer to an integer

But anywhere else it means get the value of. Example:

*p; //get the value at the location p points to
**p; //get the value at the location that the value at the location that p points to points to

'course, if you understand that last line, you probably don't need my help. A step-by-step example with s:

*(*s); //equivalent to **s (I think). *s says, "get the value that s points to" - s points to r, or 100004. The value there is 100012. We now have *(100012), which says "get the value at 100012", which is 100.

Note: I'm pretty sure *(100012) won't actually work, so don't try it.

Hopefully that clears it up a bit.

The last one looks right. It doesn't reflect the addresses provided by the diagram, but it probably shouldn't.

admanb

By the way, is "p1 [100]", "x [5]", etc, your professor's notation? Because it looks like array notation, even though it's clearly not, which confuses things. :P

Jeice

Oh the [] is suppose to be a box, I just didn't know how to upload a picture or make a box -_-"

But stepping away from the problem and re-looking at it now, I finally understand it. Thanks guys!