1. Pointers
Pointers are variables that contain memory addresses as their values.
A variable name refers to a specific value.
A pointer contains an address of a variable that refers to a specific value.
A variable directly references a value.
A pointer indirectly references a value.
Referencing a value through a pointer is called indirection.

2. Operators & ‘address of’ returns the address of an object or variable
* ‘value of’ refers to the value at a given address

3. Directly and Indirectly referencing a variable
int Sum = 5;
int X = 3;
int* z = &X;
Address
Name
Value
100011
Sum 5
100100 X 3
z=100100, *z=3, &Sum=100011

4. Initialization A pointer may be initialized to 0 , NULL or an address.
NULL is a symbolic constant defined in <stdio.h>
A pointer with the value NULL points to nothing.
The only integer that should be assigned to a pointer is 0.
Dereferencing
The * operator – indirection or dereferencing operator, returns the value of the object that its operand points to in memory. This is called dereferencing the pointer.

5. /* Program to display the address and value of a pointer */
#include <stdio.h>
int main() {
int a;
int *aPtr;
a = 200;
aPtr = &a;
printf(“The address of a is %p \n”, &a);
printf(“The value of aPtr is %p \n”, aPtr);
printf(“The value of a is %d \n”, a);
printf(“The value of *aPtr is %d \n”, *aPtr); }

6. Calling functions by reference
#include <stdio.h>
void cubebyref( int *);
int main() {
int num = 5;
printf(“The number is %d \n”,num);
cubeByRef(&num);
printf(“The new value of number is %d \n”,num);
return 0; }
void cubeByRef(int *numPtr)
*numPtr = *numPtr * *numPtr * *numPtr ;

7. Relationship between Pointers and Arrays
An array name is the address of the first element of an array.
int b[5];
The address of the first element : b, &b[0]
Assume that int b[5] and pointer variable bPtr have been declared. Since the array name is a pointer to the first element of the array:
int* bPtr = b;
is equivalent to int* bPtr = &b[0];
Array element b[1] can be referenced by:
*( bPtr + 1)
1 is the ‘offset’ with respect to the pointer.
This notation is called pointer / offset notation.

8. In pointer/offset notation, the offset is the same as the array subscript.
Pointers can be subscripted exactly as arrays can.
bPtr[1] refers to the array element b[1].
This is called pointer / subscript notation.

9. #include <stdio.h>
int main() {
int b[] = { 10 , 20 , 30 , 40 };
int *bPtr = b;
int i, offset;
printf(“Pointer/offset notation where the pointer is ”);
printf(“the array name \n”);
for(offset = 0; offset < 4; offset++)
printf(“*(b + %d) = %d \n”, offset, *( b + offset) );
printf(“Pointer/subscript notation \n”);
for( i = 0 ; i < 4 ; i++)
printf(“bPtr[ %d ] = %d \n”, i, bPtr [i ]);
printf(“pointer/offset notation \n”);
for (offset = 0; offset < 4 ; offset ++)
printf(“ *(bPtr + %d) = %d \n”, offset,*(bPtr + offset));
return 0; }

10. #include <stdio.h>
void copy( char *, const char *);
int main() {
char string1[10], *string2 = “CS230”;
char string3[10], string4[ ] = “Lab”;
copy(string1, string2);
printf(“string1 = %s \n”,string1);
copy(string3,string4);
printf(“string3 = %s \n”,string3);
return 0; }

11. void copy(char *s1, const char *s2){
int i = 0; do
s1[i] = s2[i];
i++; }
while (s2[i] != ‘\0’);
s1[i] = ‘\0’;