7/28/2019 15Lect Array 1st Continue

1/14

7/28/2019 15Lect Array 1st Continue

2/14

What Are Arrays?

It is a data structure

Unlike a variable used to store a single value,

e.g int debt = 2;

It is used to store series of values of the same type, sequentially

The whole array bears a single name, and the individual items, or

elements, are accessed by using an integer index e.g int debts[10];//int is the datatype

//debts is name of array//and 20 is the number of elements //contained in an

array

1

debts

2

debt

7/28/2019 15Lect Array 1st Continue

3/14

How the Compiler recognizes an Array?

Just like variables and functions array have to be declared beforetheir usage.

Declaration of array;/* some array declarations */

int main(void)

{

float a[365]; /* array of 365 floats */

char b[12]; /* array of 12 chars */

int c[50]; /* array of 50 ints */

int debts[10]; /* array of 10 ints */

... }

Above [] brackets identifies a as an array

We can access individual elements by writing its index number orsubscript in square brackets along with the array name. cont.

7/28/2019 15Lect Array 1st Continue

4/14

How to Access the Elements of Array

In C the index of an Arraystarts at index 0 and continueuntil one less then the total i.e.(10-1) in case ofdebts[10]

To access data, just writeindex of the element, we want,with the name of the array, e.g

X = debts[2];

/*this will transfer thevalue at index 2 ofdebts array, i.e. 1 tothe variable X*/

1

2

1

.

.

.

5

8

debts[0]

debts[1]

debts[2]

debts[8]

debts[9]

.

.

.

Array Index Array Data

7/28/2019 15Lect Array 1st Continue

5/14

7/28/2019 15Lect Array 1st Continue

6/14

Initialization of An Array

A single variable can be initialized as;

int debt = 2;

Array Initialization;#define NUM = 8; /*constant, a good prog. practice*/

int main(void)

{

int powers[NUM] = {1,2,4,6,8,16,32,64}; /* ANSI only */

... }comma-separated list of values enclosed in braces form

the elements of an array

7/28/2019 15Lect Array 1st Continue

7/14

7/28/2019 15Lect Array 1st Continue

8/14

Initialization cont.

/* some_data.c -- partially initialized array */

#include

#define SIZE 4int main(void)

{

int some_data[SIZE] = {1492, 1066};

int i;

printf("%2s%14s\n", "i", "some_data[i]");

for (i = 0; i < SIZE; i++)printf("%2d%14d\n", i, some_data[i]);

return 0;

}

This time the output looks like this:

i some_data[i]0 1492

1 1066

2 0

3 0

Which means partial initialization, also set the other memory locations to 0;

7/28/2019 15Lect Array 1st Continue

9/14

Initialization cont

Another way;

const int days[] = {31,28,31,30,31,30,31,31,30,31};

//compiler sets the number of items to 10 automatically

Designated Initialization;

int arr[6] = {0,0,0,0,0,212}; // traditional syntax

int arr[6] = {[5] = 212}; // initialize arr[5] to 212

if we want to initialize just one element of array,former is the traditional way, and later is the newC99 method.

7/28/2019 15Lect Array 1st Continue

10/14

Assigning Values to Arrays

We can use loops for assigning values to array

in addition to assignment at initialization

Some wrong methods of assignment;/* nonvalid array assignment */

#define SIZE 5

int main(void){

int o[SIZE] = {5,3,2,8}; /* ok here */

int y[SIZE];

y = o; /* not allowed */

y[SIZE] = o[SIZE]; /* invalid */

y[SIZE] = {5,3,2,8}; /* doesn't work */

}

7/28/2019 15Lect Array 1st Continue

11/14

Array Bounds

C compiler wont check the boundary of your array, so its theprogrammer responsibility.

Reason! To make C faster.

How to avoid!

Use a symbolic constant for length of Array index,

Remember that indexing starts at 0 in C.int n = 5;

int m = 8;

float a1[5]; // yes

float a2[5*2 + 1]; // yes

float a3[sizeof(int) + 1]; // yes

float a4[-4]; // no, size must be > 0

float a5[0]; // no, size must be > 0

float a6[2.5]; // no, size must be an integer

float a7[(int)2.5]; // yes, typecast float to int constant

float a8[n]; // not allowed before C99

float a9[m]; // not allowed before C99 VLA

7/28/2019 15Lect Array 1st Continue

12/14

Multidimensional Arrays

Declaration;int box[2][2];int box[2][2][2]; //uptil 26 in Bloodshed DevC

Initialization;Int box[2][2] = { {1, 2}, {3, 4} }; //two col and rows

Int box[2][2][2] = {

{ {1,2}, {3, 4} },

{ {5,6}, {7, 8} }

};

7/28/2019 15Lect Array 1st Continue

13/14

Passing Arrays to Function

#include

int sum(int arr[]);

int main(void){

int i ;

int arr[4];

long answer;

for (i = 0; i < 4; i++)

arr[i] = 2*i;

answer = sum(arr);

for (i = 0; i < 4; i++)

printf("index = %d, value = %d\n", i, arr[i]);

printf("result = %d\n", answer);

}

int sum(int arr[])

{ int i;

int result = 0;

for (i = 0; i < 4; i++)

result = arr[i] + result;return (result);}

7/28/2019 15Lect Array 1st Continue

14/14