POINTERS AND ARRAYS
SUB TOPICS :
- Pointer Definition
- Pointer Concept
- Pointer to Pointer
- Array
• Pointer
is a variable that store the address of another variable
• Syntax
:
<type>
*ptr_name;
• Two
operators mostly used in pointer : * (content of) and & (address of)
• Example:
Initialize an integer pointer into a data variable:
int i, *ptr;
ptr = &i;
To assign a new value to the variable pointed by the
pointer:
*ptr = 5; /* means
i=5 */
Pointer to Pointer
· Pointer to pointer is a variable that saves another address of a pointer
· Syntax:
§ <type> **ptr_ptr ;
· Example:
o int i, *ptr, **ptr_ptr;
o ptr = &i;
o ptr_ptr = &ptr;
o To assign new value to i:
o *ptr = 5; // means i=5 ;
o **ptr_ptr = 9; // means i=9; or *ptr=9;
Array Definition
• Data
saved in a certain structure to be accessed as a group or individually. Some
variables saved using the same name distinguish by their index.
• Array
characteristics:
–
Homogenous
All
elements have similar data type
–
Random Access
Each
element can be reached individually, does not have to be sequential
type array_value
[value_dim];
• Example :
int
A[10];
• The
definition consists of 4 components:
–
Type specified
–
Identifier (name of the array)
–
Operator index ([
])
–
Dimensional value inside operator [ ]
Array Initialization
•
Array can be initialized explicitly without
dimensional value declaration
– Example:
int B[
]={1, 2, -4, 8};
Array
B has 4 elements
– Example:
int
B[8]={1, 2, -4, 8};
Accessing Array
*(A+2) or A[2]
•
A is equivalent with &A[0] or a constant
pointer to the first element of particular array
•
To show A[2] on the monitor
screen:
printf(“%d”,A[2]) or
printf(“%d\n”,*(A+2));
•
Pointer variable is a pointer that can be assigned with new value at run-time.
•
Pointer constant is a pointer that can not be assigned with new value at run-time
•
Array is Pointer Constant to its first element of the array. Array can be filled with pointer
variable.
•
Example:
– int x=10, y=20;
– int *ptr; //ptr
is pointer variable
– ptr = &x;
– ptr = &y;
Two Dimensional Array
/* Printing out array 2-D */
#include <stdio.h>
void main() {
int
two_dim[3][5] = {1, 2, 3, 4, 5,
10, 20, 30, 40, 50,
100, 200, 300, 400, 500};
int
i, j;
for
(i=0; i<3; i++){
for
(j=0; j<5; j++) printf("%6d", two_dim[i][j]);
printf("\n");
}
}
•
String is an array of character that ended with
null character ( ‘\0’ or in ASCII = 0)
•
String constant or string literal is some characters
written between double quote
– Example:
”Welcome to Binus”
– String
constant type is pointer constant, thus can be assigned to an array of
character :
– Example
:
char
name[40] = ”Amir”; //ok
name
= ”Amir”; // error name is a constant
pointer
Name[40]=
“Amir”; //error
•
In Standard Library Function (header file string.h) provides
functions to manipulate string:
– strlen()
Return
a value of string length; excluded null char
– strcpy(s1,s2)
Copy
s2 to s1
– strncpy(s1,s2,n)
Copy
first n characters of s2 to s1
– strcat(s1,s2)
Adding string s2 to the
end of string s1
– strncat(s1,s2,n)
Adding
n characters of string s2 to the end of string s1
– strcmp(s1,s2)
Comparing
the value of string s1 and s2, if similar returning 0
– etc.
•
Pointer is a variable that store the address of
another variable
•
Pointer to pointer is a variable that saves another
address of a pointer
•
Data saved in a certain structure to be accessed as a
group or individually. Some variables saved using the same name distinguish by
their index which called as an array
•
String is an array of character that ended with null
character
2201760945
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Kevin Orlando Sutanto
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