16. What is a pointer variable?

Ans:
A pointer variable is a variable that may contain the address of another variable or any valid address in the memory.

Ex - 1:  What is the output?
. void main()
{
            int  const * p=5;
            printf("%d",++(*p));
}

Ans:
Compiler error: Cannot modify a constant value.
Explanation:   
p is a pointer to a "constant integer". But we tried to change the value of the "constant integer".

Ex - 2 what is the output?:

main()
{
             int c[ ]={2.8,3.4,4,6.7,5};
             int j,*p=c,*q=c;
             for(j=0;j<5;j++) {
                        printf(" %d ",*c);
                        ++q;     }
             for(j=0;j<5;j++){
printf(" %d ",*p);
++p;     }
}
 
Ans:
                        2 2 2 2 2 2 3 4 6 5

Explanation:

Initially pointer c is assigned to both p and q. In the first loop, since only q is incremented and not c , the value 2 will be printed 5 times. In second loop p itself is incremented. So the values 2 3 4 6 5 will be printed.