Data Structure Topic: Arrays Duration: 2 hr

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Data Structure

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To be able to define arrays

To familiarize array initialization

To perform bounds checking in arrays

To apply passing array elements to a function

To apply passing an entire array to a function

To be able to apply 2-dimensional array

To illustrate memory map of a 2-dimensional array

To use pointers to an array

To familiarize and apply array of pointers

To be able to apply 3-dimensional array

To be able to apply n-dimensional arrays in problem solving

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Scalar variables – capable of holding a single data item.

Aggregate variables – stores collections of values.

Two kinds of aggregate variables:

- Array and Structure

The C language provides a capability that enables the user to

design a set of similar data types, called

Array

.

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Suppose we wish to arrange the percentage marks obtained by

100 students in ascending order.

In such a case we have two options to store these marks in memory:

(a) Construct 100 variables (scalar) to store percentage marks

obtained by 100 different students, i.e. each variable containing

one student’s marks.

(b) Construct one variable (an aggregate called array or subscripted

variable) capable of storing or holding all the hundred values.

The second is better, for it is much easier to handle 1 variable than

with 100 different variables.

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Definition:

◦ Is a collective name given to a group of similar quantities/elements

Example:

◦ Representing marks obtained by five students

per = { 48, 88, 34, 23, 96 }

accessing the numbers in the group is through its position/location starting from 0, say,

accessing 88 would refer to per [1], and accessing 23 to per [3], … per [i] to refer to any location i

where the per is the subscripted variable (array), whereas i is its

subscript/index

Arrays …

48 88 34 23 96

per[0]

per[1]

per[2]

per[3]

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Similar elements could be

◦

All ints

◦

All floats

◦

All chars

Array of characters is called ‘string’

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main( ) {

int avg, sum = 0 ; int i ;

int marks[30] ; /* array declaration */

for ( i = 0 ; i <= 29 ; i++ ) {

printf ( "\nEnter marks " );

scanf ( "%d", &marks[i] ); /* store data in array

*/ }

for ( i = 0 ; i <= 29 ; i++ )

sum = sum + marks[i] ; /* read data from an array*/

avg = sum / 30 ;

printf ( "\nAverage marks = %d", avg ) ; }

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Purpose:

◦

To let the compiler

● know what kind of array, and

● how large an array we want

Syntax:

data_type array_name [ integer_size ];

Example:

int marks [30] ;

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Done with subscript, the number in the brackets

following the array name

◦

The number specifies the element’s position in the array

◦

All elements are numbered starting at

0 to size-1

◦

Use of a variable like

i

to refer to various elements of the array

Example:

marks[i]

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Example:

for ( i = 0 ; i <= 29 ; i++ ) {

printf ( "\nEnter marks " ); scanf ( "%d", &marks[i] ); }

Program flow:

The for loop causes the process of asking for and receiving a student’s marks from the user to be repeated 30 times. The first time through the loop, i has a value 0, so the scanf( ) function will cause the value typed to be stored in the array

element marks[0], the first element of the array. This process will be repeated until i becomes 29. This is last time through the loop, which is a good thing, because there is no array element like marks[30].

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Example:

for ( i = 0 ; i <= 29 ; i++ ) sum = sum + marks[i] ;

Program flow:

The for loop is much the same, but now the body of the loop causes each student’s marks to be added to a running total stored in a variable called sum. When all the marks have been added up, the result is divided by 30, the number of

students, to get the average.

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Example:

int num[6] = { 2, 4, 12, 5, 45, 5 } ;

int n[ ] = { 2, 4, 12, 5, 45, 5 } ;

float press[ ] = { 12.3, 34.2 -23.4, -11.3 } ;

Note:

(a) Till the array elements are not given any specific values,

they are supposed to contain garbage values.

(b) If the array is initialized where it is declared, mentioning

the dimension of the array is optional as in the 2

nd

example

above

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If initializer is shorter than array

int num[6] = { 2, 4, 12 } ;

/* initial value of a is 2, 4, 12 , 0, 0, 0 */

Initializing array to all zeros

int num[6] = { 0 } ;

/* initial value of a is 0, 0, 0, 0, 0, 0 */

Designated initializers

int num[6] = { [2]=12, [4]=45 } ;

/* initial value of a is 0, 0, 12, 0, 45, 0 */ int n[ ] = { [2]=12, [4]=45 } ;

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Consider the following array declaration:

int arr [8];

For a 32-bit system, each integer element gets 2 bytes each, thus, making

it 16 bytes get immediately reserved in memory.

Since the array has not been initialized, all 8 values present in it would be

garbage values.

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In C there is no check to see if the subscript used for an array exceeds the size of the array.

Data entered with a subscript exceeding the array size will simply be placed in memory outside the array; probably on top of other data, or on the program itself.

This will lead to unpredictable results, to say the least, and there will be no error message to warn you that you are going beyond the array size.

In some cases the computer may just hang.

Thus, to see to it that we do not reach beyond the array size is entirely the programmer’s botheration and not the compiler’s.

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#include <stdio.h> #define MAX 10

main () {

int arr[MAX]={0}, i, sum=0;

printf("Please input 10 integer values.\n");

for(i=0; i<MAX; i++) { scanf("%d", &arr[i]); }

for (i=0; i<MAX; i++) { sum += arr[i];

}

printf("The sum is %d.", sum); return 0;

}

Example #1:

Sum of

Array of Integers

Sets maximum size of an array Sets all 10 element values to zero

Stores 10 integer inputs from the keyboard

Sums all10 integers from arr[ ]

Please input 10 integer values. 1 2 3 4 5 6 7 8 9 10

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main () {

int arr[MAX]={0}, arrDup[MAX]={0}, i, sum=0; printf("Please input 10 integer values.\n");

for (i=0; i<MAX; i++) { arrDup[i]= arr[i];

}

for(i=0; i<MAX; i++) { printf("%4d", arrDup[i]); } return 0; }

Example #2:

Duplicating Arrays

An array storing the same integer values of arr [ ]

1 2 3 4 5 6 7 8 9 10

arr[0] = 1 arr[1] = 2 …

arr[8] = 9 arr[9] = 10

arrDup[0] = 1 arrDup[1] = 2

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main () {

int arr[MAX]={0}, i, searchVal, found=0; printf("Please input 10 integer values.\n");

printf("What value to be searched? "); scanf("%d", &searchVal);

for (i=0; i<MAX; i++) { if (searchVal == arr[i]) { found=1; break; } }

if(found) printf("\nThe value is in the array."); else printf("\nThe value is not in the array."); return 0;

}

Example #3:

Finding

Values in an Array

What value to be searched? 2

arr[0] = 1 arr[1] = 2 …

arr[8] = 9 arr[9] = 10

match with 2?

No Yes

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Problem Definition:

Create a program that will accommodate at most 10

entries from the user. During execution the user will be

inputting values of at most 10. The program will then

sort the values and displays the sorted list.

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Write a program that prints a table showing the value of $100

invested at different rates of interest over a period of years. The user

will enter an interest rate and the number of years the money will be

invested. The table will show the next four higher rates – assuming

that interest is compounded once a year. Here’s what the session

would look like:

Enter interest rate: 6% Enter number of years: 5

Programming Exercise (2)

Years

6%

7%

8%

9%

10%

1

106.00

107.00

108.00

109.00

110.00

2

112.36

114.49

116.64

118.81

121.00

3

119.10

122.50

125.97

129.50

133.10

4

126.25

131.08

136.05

141.16

146.41

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Construct a flowchart (6 pts) for the program defined

below:

The program prompts the user to enter a series of

numbers, then writes the numbers in reverse order:

Implement afterwards your solution (4 pts).

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Write a program that will check an integer value if

it has repeating digit.

Example:

Number =54342

Repeated Digit

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Write a program with a function that adds all digits

of an integer number.

Example:

Number =94356

Sum = 27

Requirement:

int sumOfDigits(int num) { … }

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#include <stdio.h>

#define SIZE 9

swap (int a, int b)

{

int t ;

t = *a ;

a = b ;

*b = t ;

}

Passing Array Elements to a Function

int main () {

int i, a[SIZE]={[2]=34,

[5]=11, [8]=-13, [7]= 8};

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

printf("%d\n",a[i]);

for (i=0;i<SIZE/2;i++) {

swap(&a[i],&a[SIZE-1-i]);

}

printf("\nReverse

Order.\n");

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

printf("%d\n",a[i]);

return 1;

}

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Address of the array at index is submitted to the function –

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Create a function that searches a number in the array and returns the

first location of the number

int searchN(int arr[], int s, int n) {...}

Example:

array = {0, 13, 4, 11, 9, 4, 2, 58, 1}

search number = 4

location at = 3

array = {0, 13, 4, 11, 9, 4, 2, 58, 1}

search number = 2

location at = 7

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Passing an Entire Array to a Function

#include <stdio.h> #define SIZE 9

swap (int *a, int *b) { int t ;

t = *a ; *a = *b ; *b = t ; }

reverse (int a[], int s) { int i=0;

for (i=0;i<SIZE/2;i++) { swap(&a[i],&a[SIZE-1-i]);

} }

int main () {

int i, a[SIZE]={[2]=34, [5]=11, [8]=-13, [7]= 8};

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

printf("\nReverse Order.\n"); reverse(a,SIZE);

for (i=0; i<SIZE;i++) printf("%d\n",a[i]); return 1;

}

Address of the array is submitted to the function –

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Can determine the size of an array in bytes

◦

Example: If

a

is an array of 10 integers, then

sizeof(a)

is

20 (assuming each integer type requires

2 bytes)

Can measure the size of an array element

◦

Example:

sizeof(a)/sizeof(a[0])

Example use:

for(i=0; i<(int)(sizeof(a)/sizeof(a[0])); i++)

a[i]=0;

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sizeof(a)/sizeof(a[0])

OR

Defining if with macro

#define SIZE

((int)(sizeof(a)/sizeof(a[0])))

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Code to Example: Computing Interest

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Constant Arrays

Array declared as constant should not be modified by the program

Advantages:

It documents that the program won’t change the array Helps the compiler catch errors, by informing it that we don’t intend to modify the array

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Array may have N-Dimensions

Example:

◦

int m[5][9];

//creates 2D Array [row][column]

Multi-Dimensional Array

row

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Setting Dimensions and

initializers

Array is filled w/ 0 if

initializer is not enough;

last 2 rows has values of

0

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Array is filled w/ 0 if

initializer inner list isn’t

long enough to fill a row

Omitting inner braces

Initializing a Multidimensional Array

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The prototypical Internet newbie is a fellow named B1FF, who has a

unique way of writing messages, Here’s a typical B1FF communiqué:

H3Y DUD3, C 15 R34LLY C00L!!!!!!!!!!

Write a “B1FF filter” that reads a message entered by the user and

translates it into B1FF-speak:

Enter message: Hey dude, C is really cool

In B1FF-speak: H3Y DUD3, C 15 R1LLY C00L!!!!!!!!!!

Your program should convert the message to upper-case letters, substitute

digits for certain letters (A->4, B->8, E->3, I->1, O->0, S->5), and then

append 10 or so exclamation marks.

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Problem Definition:

Write a C code that

performs multiplication

of two vectors. The

procedure is as follows:

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Problem Definition:

Write a C code that performs addition of two vectors. The procedure is as

follows:

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Problem Definition:

Write a C code that performs subtraction of two vectors. The procedure is as

follows:

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Problem Definition:

Write a C code that performs inverse of a vector. The procedure is as follows:

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Problem Definition:

Write a C code that performs the transpose of a vector. The procedure is as follows: