ARRAYS AND POINTERS

1
ARRAYS AND POINTERS

• CHAPTER 6

2
What is an Array?

• int grade0, grade1, grade2
• int grade 3
• Arrays make it possible to represent large number
  of homogenous values

grade0
grade1
grade2
grade0
grade1
grade2
3
One Dimensional Arrays

• type name_of_arraysize
• int grade5

MEMORY
data
grade0
first element in array
starts from 0
data
grade1
data
grade2
data
grade3
data
grade4
fift ( the last) element in array
ends at size - 1
4
One Dimensional Arrays

• int grade5, x9, y
• grade00
• grade34
• grade2-1
• grade1grade3grade2
• grade4 x
• x grade2
• y gradegrade3

MEMORY
0
grade0
3
grade1
-1
grade2
4
grade3
9
grade4
?
x
?
y
5
INITIALIZATION

• float f1 1.0, 1.1, 1.2, 1.3 /
  declaration without the size /
• float f24 1.0, 1.1, 1.2, 1.3 /
  declaration with size /
• char z abc // char arrays
• char z a, b, c, \0
• int a800

6
EXAMPLE One Dimensional Arrays

• / array1.c/
• main()
• int x10, k
• for(k0klt10k)
• xkk
• printf(xd d\n, k, xk)
• //what will be the output ???

7
Two Dimensional Arrays define R 4 define C
5 int xRC
8
Two Dimensional Array - Memory
9
Two Dimensional Array Initialization

• int y23 1,2,3,4,5,6
• int y23 1,2,3,4,5,6
• int y3 1,2,3,4,5,6

10
Multidimensional Arrays

• int y23 // two dim.
• int z 273 // three dim
• int a223
• 1,1,0,2,0,0,
• 3,0,0,4,4,0

11
POINTERS

• int v 5 is a variable and
• 5 is the value of it
• v is the location or address of the v
• Pointers are declared in programs and then used
  to take addresses !!!
• int p
• pv

12
POINTERS

• int a1, b2, p
• pa

p
a
b
1
2
??
will point somewhere in memory
p
a
b
1
2
a
13
POINTERS

• bp
• // equivalent to ba

a
b
p
1
1 ( the value of a )
a
14
Pointers

• EXAMPLE
• include ltstdio.hgt
• int main(void)
• int i 7, j , k
• k i
• printf("sd\nsp\n", " Value of i ",
  k, "Location of i ", k)
• jk
• return 0
• NOTE table pg.250

15
CALL BY VALUE

• / Whenever variables are passed as arguments to
  a function, their values are copied to the
  function parameters /
• void main()
• int a20 int b30
• swap (a, b)
• printf(d d , a, b)
• void swap(int x, int y)
• int tmp
• tmpx
• xy
• ytmp

16
CALL BY REFERENCE

• / Pointers are passed as arguments to a
  function, their
• addresses are assigned to the function parameters
  defined as
• pointers/
• void main()
• int a20 int b30
• swap (a, b)
• printf(d d , a, b)
• void swap(int x, int y)
• int tmp
• tmp x // get value pointed by x.
• x y // assign value pointed by y to x
• y tmp

17
Relationship between Pointers and Arrays

• /An array name by itself is an adress or a
  pointer
• value /
• int a5 , p
• pa0
• // Equals to
• pa

18
Relationship between Pointers and Arrays

• a0 equals to a then a0 equals to a
• a1 equals to a1 then a1 equals to (a1)
• a2 equals to a2 then a2 equals to (a2)
• ai equals to ai then ai equals to (ai)
• EXAMPLE
• int a 51,2,3,4,5
• int p
• printf(d,a0) printf(d,a)
• printf(d,a2) printf(d,(a2))
• pa4
• Pa4

19
Storage mapping function

• the mapping b/w pointer values and array indices
• EXAMPLE
• int d 3
• di?(d0i)
• EXAMPLE
• int a 3 4
• aij ? (a004ij)

20
Pointer Arithmetic

• EXAMPLE
• double a2,p,q
• pa // pa0
• qp1 // qa01 a1
• printf(d\n, q-p) / difference in terms of
  array elements/
• printf(d\n, (int) q-(int) p) / difference in
  memory locations/

21
Arrays as Function Arguments

• main()
• int x9, r
• rsum(x,9) //sum(x0,9)
• double sum( int a, int n)
• int i
• double result 0.0
• for (i0 iltn i)
• resultai
• return result

• main()
• int x9, r
• rsum(x,9) // sum(x0,9)
• double sum( int a, int n)
• int i
• double result 0.0
• for (i0 iltn i)
• result(ai)
• return result

22
Dynamic Memory Allocation

• Calloc contiguous memory allocation
• Malloc memory allocation

23
CALLOC

• calloc(n, el_size) ?an array of n elements, each
  element having el_size bytes
• int main()
• int a //will be used as an array
• int n // size of array
• ....
• acalloc(n, sizeof(int)) / get space for a ,
  and initialize each bit to zero /
• free(a) / each space opened dynamically must
  be returned /

24
MALLOC

• / malloc does not initialize memory /
• int main()
• int a //will be used as an array
• int n // size of array
• ....
• amalloc(nsizeof(int)) / get space for a /
• ....
• free(a)