C109: Pointers

Pointer is a special type of variable that points to another variable. Like a variable it is a location in a memory to store data. Data that it stores is an address. Like any other variables, pointer need to be declared.

dataType *pointerName;

data type is same as the data type of the variable its pointing to. The data type can be int, float, double or char. A pointer name is like a normal variable but a asterisk sign '*' is places before the pointer name, to tell the compiler that it is a pointer.

The value assigned to a pointer is a long hexadecimal number that represents the address of the variable it is pointing to. Following is syntax for assigning an address to pointer:

pointerName = &variableName;

Following example shows how address of varA is assigned to ptr. Both varA and ptr is integer.

int *ptr;
int varA;

varA = 213
ptr = &varA;

to display the value stored by variable pointed by pointer

printf("Variable value pointed by pointer: %d\n", *ptr);

this will output

Variable value pointed by pointer: 231

if we write ptr without the asterisk like shown in code below, we are actually referring to the address this pointer stores.

printf("Variable value pointed by pointer: %d\n", ptr);

it will display the address of the varA. This is one of the common misunderstanding we might face when using pointer.

Variable value pointer by pointer : d3efc7d8

the address printed in the previous code is suppose to be same as when we write the following code:

printf("Address of varA : %d\n", &varA);

and the output is:

Address of varA : d3efc7d8

We can also do arithmetic operations on pointer. For example, we can increment the address to next address location in memory by adding 1.