Transcript One dimensional Arrays

One dimensional 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 list[25], a[10]; /* 10 elements in a referenced by
a[0], a[1],……., a[9] */
double x[20];
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example
/*
* Example of a simple list of integers
*/
#include <stdio.h>
int main(void)
{
int res[10]; /* Note! index = 0..9 */
int i;
}
for (i=0;i<=9;i++)
{
res[i] = 10-i;
printf("res[%d]=%d\n",i,res[i]);
}
return 0;
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Initialization
• The elements can be initialized at declaration
int res[10]={10,9,8,7,6,5,4,3,2,1};
• If the initializing list is shorter, the rest of the elements are 0
int res[10]={0}; /* all elements are initialized to
0 */
• The number of elements can be omitted if all elements in
the array are initialized at declaration
int res[]={10,9,8,7}; /* 4 elements with
index 0..3 */
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Indexing
arrayname[integral 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 x[10];
int n;
printf(”How many elements should you type (<11): ”);
scanf(”%d”, &n); /* should be validated! */ fflush(stdin);
for (i=0; i<n; i++)
scanf(”%lf”, &x[i]);
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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 <stdio.h>
#include <math.h>
#define MAX_ITEM 8 /* maximum number of items in list */
int
main(void)
{
double x[MAX_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\n> ", MAX_ITEM);
for (i = 0; i < MAX_ITEM; ++i)
scanf("%lf", &x[i]);
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/* Computes the sum and the sum of the squares of all data */
sum = 0;
sum_sqr = 0;
for
(i = 0; i < MAX_ITEM; ++i) {
sum += x[i];
sum_sqr += x[i] * x[i];
}
/* 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 < MAX_ITEM; ++i)
printf("%3d%4c%9.2f%5c%9.2f\n", i, ' ', x[i], ' ',
x[i] - mean);
}
return (0);
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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 < n; ++i)
list[i] = in_value;
Introduce the concept of
int *list
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Returning an Array Result
• A function can’t 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 < n; ++i)
arsum[i] = ar1[i] + ar2[i];
}
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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
<stdlib.h>
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
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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 <stdlib.h>
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 < n; ++i)
ar_sum[i] = ar1[i] + ar2[i];
return (ar_sum);
}
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How to call add_arrays() 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 <math.h>
#include <stdlib.h>
int main(void){
double list1[20], list2[20], add_lists[20], *sum_lists;
int n=5, i;
/* generate 10 random numbers, 5 in each array list1 and list2 */
for (i=0; i<5; i++){
list1[i]= (double) rand()/(double)RAND_MAX*10;
list2[i]= rand()/(double)RAND_MAX*10;
}
add_arrays(list1, list2, add_lists, n);
sum_lists = add_arrays2(list1, list2, n);
printf(”\nLIST1
LIST2
ADD_ARRAYS
ADD_ARRAYS2\n”);
for (i=0; i<5; ++i)
printf(”%8.4f%8.4f%12.4f%15.4f\n”,
list1[i],list2[i],*(add_lists+i),sum_lists[i]);
free(sum_lists);
return 0;
}
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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
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Sorting
A list of n integers list1, list2, list3, …, listn . The elements should be
ordered such that listi <= listi+1 ; i=1,2,…n-1
Algoritm BubbelSort(lista,n) /*Lightest value bubbles
to top*/
bytt = false
last = n
repeat
for i=1 to last-1 do /* push the heaviest value to
the bottom */
begin
if list i > listi+1
then begin
exchange values
bytt = true
end
end
last = last - 1
until not bytt
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Code
void bubble_sort(int list[], int n) {
int
i, last, bytt, temp;
do{
last = n; /* initialization */
bytt = 0; /* logical false */
for (i=0; i <= last-1; i++)
{
if (list[i] > list[i+1]) {
temp = list[i];
list[i] = list[i+1];
list[i+1] = temp;
bytt = 1; /* logical true */
} /* end of if */
}/* end of for */
last = last - 1;
}while (bytt);
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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
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Strings
void main(void)
{
char strng[10]; /* Note! indeces = 0..9 */
int i;
printf("--------- example 1 ---------\n\n");
printf("Type a string : ");
scanf("%s", strng); fflush(stdin);
printf("-->%s<--\n\n", strng);
}
printf("Type another string : ");
gets(strng);
printf("-->%s<--\n", strng);
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Run
----------- example 1 ----------Type a string : like this
-->like<-Type a string : like this
-->like this<--
What will happen if we type more than 10 charcters? In the
second scanf()?
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String functions
 include <string.h>
 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 <, ==,
> string2
 strcpy(string1, string2) copies string2 to string1 , a
pointer to string1 is returned
 strlen(string) number of characters before \0 is returned
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strcat
#include <string.h>
void main(void)
{
char str1[] = "First string";
char str2[] = "Second!";
char str3[] = "Third";
printf("--------- example 2 ---------\n\n");
printf("-->%s<--\n",strcat(str1,str2));
printf("-->%s<--\n",str1);
printf("-->%s<--\n",strcat(str3,str1));
printf("-->%s<--\n",str3);
printf("------- concatenating -------\n\n");
}
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Run
----------- example 2 ------------>First stringSecond!<--->First stringSecond!<--->ThirdFirst stringSecond!<--->ThirdFirst stringSecond!<---------- concatenating ---------
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