Thread: A multi part Q

Originally posted by pxleyes
c) You can only add pointers. There is no pointer subtraction.

http://www.eskimo.com/~scs/cclass/notes/sx10c.html

Originally posted by pxleyes
h) The address of q is copied to to the address of p for the same reason as stated in g.

The value of q is copied to the value of p. (The value happens to be an address but the addresses of p and q stay the same)

Thanks major for that info.

Can any of you explain what linuxdude said in reference to part j. I am slightly confused about that one.

THe reason I ask is because I was evalusating anothing question, and i plugged it into a compiler and i got no error. see below:

Code:

int main()
{
int *zPtr;
int *aPtr = NULL;
int number, i;
int z [5] = {1, 2, 3, 4, 5};
zPtr = z;

number = *zPtr; /* use pointer to get the first value of the array */
number = zPtr [2]; /* assign element with subscript 2 to number */
for (i = 0; i <= 4; i++) { /* print array z using zPtr */
     printf("%d", zPtr[i]);
      }

      system("PAUSE");
      return 0;
}

Try compiling with zPtr = z[1]. It will probably compile, but you should get warnings and weird things will probably happen when you run it.

z[1] is not an address but a value.

number is a normal integer in your example. but in the your original post it is a pointer ot type int; any questions feel free to ask
here is the gcc error with it as type int

Code:

test.c:13: warning: assignment makes pointer from integer without a cast

Try asking your compiler.

Code:

#include <stdio.h>

int main(void)
{
   int a [] = {5, 15, 34, 54, 14, 2, 52, 72};
   int *p = &a[1];
   int *q = &a[5];
   /* (a) What is the value of *(p+3)? */
   printf("*(p+3) = %d\n", *(p+3));
   /* (b) What is the value of *(q-3)? */
   printf("*(q-3) = %d\n", *(q-3));
   /* (c) Can I perform addition and subtraction on pointers? If so, what is q - p? */
   printf("q - p  = %d\n", (int)(q-p));
   /* (d) Is the condition p < q true or false? */
   printf("p < q  = %s\n", p < q ? "true" : "false");
   /* (e) Is the condition *p < *q true or false? */
   printf("*p<*q  = %s\n", *p<*q ? "true" : "false");
   /* (f) Can I do the following, *p = a [4]; ? */
   *p = a [4]; /* yup */
   /* (g) What happens when I do this, *p = *q; ? */
   *p = *q;
   printf("*p = %d, *q = %d\n", *p, *q);
   /* (h) What happens when I do this, p = q; ? */
   p = q;
   printf("p = %p, q = %p\n", (void*)p, (void*)q);
   /* (i) Is it legal for me to write the following line: p = a; ? */
   p = a;
   /* (j) Is it legal for me to write the following line: p = a [1]; ?
   p = a[1]; // no -- Type mismatch (assignment) (int * = int)
   */
   return 0;
}

[edit1]D'oh! Forgot the *p = *q; part (g).[/edit1]
[edit2]Grrrr. *q in printf format literal instead of q (h).[/edit2]