17. What is a pointer value and address?

Ans:
A pointer value is a data object that refers to a memory location. Each memory location is numbered in the memory. The number attached to a memory location is called the address of the location.

Ex - 1:  What is the output ?
main()
{
            char *p;
            printf("%d %d ",sizeof(*p),sizeof(p));
}
 
Ans:
                        1 2

Explanation:

The sizeof() operator gives the number of bytes taken by its operand. P is a character pointer, which needs one byte for storing its value (a character). Hence sizeof(*p) gives a value of 1. Since it needs two bytes to store the address of the character pointer sizeof(p) gives 2.

Ex - 2 Is the following code legal?
typedef struct a
    {
int x;
 aType *b;
    }aType

Ans:
No

Explanation:

The typename aType is not known at the point of declaring the structure (forward references are not made for typedefs).

Ex - 3 What is the output?
#include
main()
{
char s[]={'a','b','c','\n','c','\0'};
char *p,*str,*str1;
p=&s[3];
str=p;
str1=s;
printf("%d",++*p + ++*str1-32);
}

Ans:
77       

Explanation:

p is pointing to character '\n'. str1 is pointing to character 'a' ++*p. "p is pointing to '\n' and that is incremented by one." the ASCII value of '\n' is 10, which is then incremented to 11. The value of ++*p is 11. ++*str1, str1 is pointing to 'a' that is incremented by 1 and it becomes 'b'. ASCII value of 'b' is 98.
 Now performing (11 + 98 – 32), we get 77("M");
 So we get the output 77 :: "M" (Ascii is 77).