Arrays

1
Arrays

• A data structure (vector) with many elements of
  the same type
• A common name where individual elements are
  accessed by an index inside
• Declartion
• int list25, a10 / 10 elements in a
  referenced by
• a0,
  a1,., a9 /
• double x20

2
example
/ Example of a simple list of integers
/ include ltstdio.hgt int main(void) int
res10 / Note! index 0..9 / int i for
(i0ilt9i) resi 10-i
printf("resdd\n",i,resi) return 0
3
Initialization

• The elements can be initialized at declaration
• int res1010,9,8,7,6,5,4,3,2,1
• If the initializing list is shorter, the rest of
  the elements are 0 int res100 / all
  elements are initialized to 0 /
• The number of elements can be omitted if all
  elements in the array are initialized at
  declaration
• int res10,9,8,7 / 4 elements with index
  0..3 /

4
Indexing

• arraynameintegral expression
• Where integral expression is evaluated to an
  integer value (int or char)
• Important to keep the integral expression inside
  the range of the indeces ( see Table 7.2 on page
  310)
• An array element can be used wherever it is legal
  to use a variable of the data type in question
• Ex. 1 double x10
• int n
• printf(How many elements should you type
  (lt11) )
• scanf(d, n) / should be validated! /
• for (i0 iltn i)
• scanf(lf, xi)

5
Figure 7.2 Program to Print a Table of
Differences / Computes the mean and standard
deviation of an array of data and displays
the difference between each value and the mean.
/ include ltstdio.hgt include ltmath.hgt define
MAX_ITEM 8 / maximum number of items in list
/ int main(void) double xMAX_ITEM, / data
list / mean, / mean (average) of
the data / st_dev, / standard
deviation of the data / sum, /
sum of the data / sum_sqr / sum of
the squares of the data / int i /
Gets the data / printf("Enter d numbers
separated by blanks\ngt ", MAX_ITEM) for
(i 0 i lt MAX_ITEM i)
scanf("lf", xi)
6
/ Computes the sum and the sum of the squares
of all data / sum 0 sum_sqr 0
for (i 0 i lt MAX_ITEM i)
sum xi sum_sqr xi
xi / Computes and prints the
mean and standard deviation / mean sum /
MAX_ITEM st_dev sqrt(sum_sqr / MAX_ITEM
- mean mean) printf("The mean is
.2f.\n", mean) printf("The standard
deviation is .2f.\n", st_dev) /
Displays the difference between each item and the
mean / printf("\nTable of differences
between data values and mean\n")
printf("Index Item Difference\n")
for (i 0 i lt MAX_ITEM i)
printf("3d4c9.2f5c9.2f\n", i, ' ', xi, '
', xi - mean) return
(0)
7
Array names as formal parameters in functions
Single subscripted arrays as formal parameters
to a function are declared as in Fig. 7.4 (HOW
TO CALL IT?)
Figure 7.4 Function fill_array / Sets all
elements of its array parameter to in_value.
/ void fill_array (int list, / output -
list of n integers / int n,
/ input - number of list elements /
int in_value) / input - initial value /
int i / array subscript and loop
control / for (i 0 i lt n i)
listi in_value Introduce the concept
of int list
8
Returning an Array Result

• A function cant return a complete array but it
  can return a pointer to an array
• Another solution is to use an array name as
  output parameter (see Fig. 7.8)

Figure 7.8 Function to Add Two Arrays / Adds
corresponding elements of arrays ar1 and ar2,
storing the result in arsum. Processes first
n elements only. / void add_arrays(const double
ar1, / input - / const double
ar2, / arrays being added /
double arsum, / output - sum of
corresponding
elements of ar1 and ar2 / int n)
/ input-number of element pairs summed /
int i / Adds corresponding elements of
ar1 and ar2 / for (i 0 i lt n i)
arsumi ar1i ar2i
9
Dynamic allocation of arrays

• We can allocate space (memory cells) for an array
  by using calloc()
• Syntax double num_list
• num_list (double ) calloc(list_size, sizeof
  (double))
• Calloc() returns a pointer to void that value
  should be cast to a pointer which points to the
  data type in question
• Normally the allocated space should be freed
  before the program is ended. Use function
  free(pointername)
• Include ltstdlib.hgt to get access to calloc() and
  free()
• Ex. 1 write function add_arrays() such that it
  returns a pointer to the new array that contains
  the sum of the two arrays which are pointed to by
  the two input parameters

10
Figure 7.8 revised Function to Add Two
Arrays / Adds corresponding elements of
arrays ar1 and ar2, storing the result in
ar_sum. Processes first n elements only.
/ include ltstdlib.hgt double add_arrays2(const
double ar1, / input - / const
double ar2, / arrays being added /
int n) / input-number of element pairs
summed / int i double ar_sum ar_sum
(double ) calloc(n, sizeof(double)) /
Adds corresponding elements of ar1 and ar2 /
for (i 0 i lt n i) ar_sumi
ar1i ar2i return (ar_sum)
11
How to call add_array() and add_arrays2()
void add_arrays(const double ar1,const double
ar2, double arsum, int n) double
add_arrays2(const double ar1,const double
ar2,int n) include ltmath.hgt include
ltstdlib.hgt int main(void) double list120,
list220, add_lists20, sum_lists int n5,
i / generate 10 random numbers, 5 in each
array list1 and list2 / for (i0 ilt5 i)
list1i (double) rand()/(double)RAND_MAX10
list2i rand()/(double)RAND_MAX10
add_arrays(list1, list2, add_lists, n)
sum_lists add_arrays2(list1, list2, n)
printf(\nLIST1 LIST2 ADD_ARRAYS
ADD_ARRAYS2\n) for (i0 ilt5 i)
printf(8.4f8.4f12.4f15.4f\n,
list1i,list2i,(add_listsi),sum_listsi)
free(sum_lists) return 0
12
Result from run
LIST1 LIST2 ADD_ARRAYS
ADD_ARRAYS2 5.1387 1.7573 6.8960
6.8960 3.0863 5.3453 8.4317
8.4317 9.4763 1.7173 11.1936
11.1936 7.0223 2.2642 9.2865
9.2865 4.9477 1.2470 6.1946
6.1946
13
Sorting

• A list of n integers list1, list2, list3, ,
  listn . The elements should be ordered such that
  listi lt listi1 i1,2,n-1
• Algoritm BubbelSort(lista,n) /Lightest value
  bubbles to top/
• bytt true
• last n
• repeat
• for i1 to last-1 do / push the heaviest
  value to the bottom /
• begin
• if list i gt listai1
• then begin
• exchange values
• bytt true
• end
• end
• last last - 1
• until not bytt

14
Code
void bubble_sort(int list, int n) int i,
last, bytt, temp do bytt 0 / logical
false / for (i0 i lt last-1 i)
if (listi gt listi1) temp
listi listi listi1
listi1 temp bytt 1 / logical
true / / end of if / / end of
for / last last - 1 while (bytt)
15
Strings

• An array of characters (char)
• Simple initialization char course_name
  Programmeringsteknik the same as char
  course_name P,r,o,g,r,a,m,m,e
  ,r,i,n,g,s,t,e,k,n,i,k,\0
  
• Note \0 is automatically stored in the first
  form

16
Strings

• void main(void)
• char strng10 / Note! indeces 0..9 /
• int i
• printf("--------- example 1 ---------\n\n")
• printf("Type a string ")
• scanf("s", strng) fflush(stdin)
• printf("--gtslt--\n\n", strng)
• printf("Type another string ")
• gets(strng)
• printf("--gtslt--\n", strng)

17
Run
----------- example 1 ----------- Type a string
like this --gtlikelt-- Type a string like
this --gtlike thislt--
What will happen if we type more than 10
charcters? In the second scanf()?
18
String functions

• include ltstring.hgt
• strcat(string1, string2) concatenates two
  strings, resulting string is returned (also in
  string1)
• strcmp(string1, string2) compares string1 to
  string2, value (-,0,) is returned if string1 is
  lexiographically lt, , gt string2
• strcpy(string1, string2) copies string2 to
  string1 , a pointer to string1 is returned
• strlen(string) number of characters before \0 is
  returned

19
strcat

• include ltstring.hgt
• void main(void)
• char str1 "First string"
• char str2 "Second!"
• char str3 "Third"
• printf("--------- example 2 ---------\n\n")
• printf("--gtslt--\n",strcat(str1,str2))
• printf("--gtslt--\n",str1)
• printf("--gtslt--\n",strcat(str3,str1))
• printf("--gtslt--\n",str3)
• printf("------- concatenating -------\n\n")

20
Run
----------- example 2 ----------- --gtFirst
stringSecond!lt-- --gtFirst stringSecond!lt-- --gtThir
dFirst stringSecond!lt-- --gtThirdFirst
stringSecond!lt-- --------- concatenating
---------