ARRAYS, POINTERS, AND STRINGS

1
ARRAYS, POINTERS, AND STRINGS

• CHAPTER 6
• (PART 1 arrays and pointers)
• prepared by Senem Kumova Metin
• modified by Ilker Korkmaz

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What is an Array?

• int grade0, grade1, grade2
• int grade 3
• Arrays represent a group of homogenous typed
  values

grade0
grade1
grade2
grade0
grade1
grade2
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One Dimensional Arrays (1)

• type name_of_arraysize
• int grade5

MEMORY
data
grade0
first element in array
starts from 0
data
grade1
data
grade2
data
grade3
data
grade4
fifth ( the last) element in array
ends at size - 1
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One Dimensional Arrays (2)

• int grade5, x9, y0
• grade00
• grade34
• grade2-1
• grade1grade3grade2
• grade4 x
• x grade2 //the value of x ?
• y gradegrade3 //the value of y ??

MEMORY
0
grade0
3
grade1
-1
grade2
4
grade3
9
grade4
?
x
??
y
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Array Initialization

• float f1 1.0, 1.1, 1.2, 1.3 /
  declaration without size /
• float f24 1.0, 1.1, 1.2, 1.3 /
  declaration with size /
• char z abc // special char arrays strings
• char z a, b, c, \0
• int a800 // initializes all the elements
  to zero

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Example One Dimensional Arrays

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

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Two Dimensional Arrays (1) define R 4
define C 5 int xRC
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Two Dimensional Arrays (2)
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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

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POINTERS (1)

• int v 5
• v is the identifier of an integer variable
• 5 is the value of v
• v is the location or address of the v inside the
  memory
• means the address of
• Pointers are used in programs to access memory.
• int v 5
• int p // p is the identifier of a pointer
  to an integer
• pv // p is assigned with the address of v
• p0 // OR p NULL

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POINTERS (2)

• int a1, b2, p
• pa

p
a
b
1
2
??
will point somewhere in memory
p
a
b
1
2
a
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POINTERS (3)

• bp
• // equivalent to ba

a
b
p
1
1 ( the value of a )
a
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Example 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 pg.250 of the textbook

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CALL BY VALUE

• / Whenever variables are passed as arguments to
  a function, their values are copied to the
  function parameters , and the variables
  themselves are not changed in the calling
  environment./
• int main()
• int a20 int b30
• swap (a, b)
• printf(d d , a, b)
• return 0
• void swap(int x, int y)
• int tmp
• tmpx
• xy
• ytmp
• return

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CALL BY REFERENCE

• / Whenever addresses of variables are passed as
  arguments to a function, their values shall be
  changed in the calling environment./
• 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
• return

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Relationship between pointers and
arrays (1)

• / The name of an array is the adress or the
  pointer to the first element of the array. /
• int a5 , p
• pa // OR pa0

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Relationship between pointers and
arrays (2)

• 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

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Storage mapping

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

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Pointer Arithmetic

• EXAMPLE
• double a2,p,q
• pa // pa0
• qp1 // qa01 which means qa1
• printf(d\n, q-p) / the difference in terms
  of array elements (1 is
  printed)/
• printf(d\n, (int) q - (int) p) / the
  difference in memory
  locations (8 is printed)/
• Why 8 ??

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Arrays as Function Arguments

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

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

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Dynamic Memory Allocation

• calloc Contiguous memory ALLOCation
• malloc Memory ALLOCation

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calloc

• calloc(n, el_size)
• an array of n elements, each element having
  el_size bytes
• void 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 allocated dynamically
  should be returned /

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malloc

• / malloc does not initialize memory /
• void main()
• int a //will be used as an array
• int n // size of array
• printf(give a value for n)
• scanf(d,n)
• amalloc(nsizeof(int)) / get space for a
  (allocate a)/
• ....
• free(a)