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Arrays

Fundamentals of Computing (ESc 101A)Lecture Notes 6

Raghunath [email protected]

Indian Institute of Technology, Kanpur

Raghunath Tewari [email protected] ESc101A
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ArraysDefinition and Notation

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Arrays are variables that contain a list of values (multiple) ofthe same type.

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For example, considerint ar[10];


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The above statement, declares an array ar of type int, andallocates memory to store 10 different values.

- Name: ar- Type: int- Size: 10


A
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Question: If the array ar is storing 10 values, how do we referto them individually?


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The 10 values are referred by ar[0], ar[1], ar[2],ar[3], ar[4], ar[5], ar[6], ar[7], ar[8] and ar[9].


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The 10 values are referred by ar[0], ar[1], ar[2],ar[3], ar[4], ar[5], ar[6], ar[7], ar[8] and ar[9].

Note that the indices run from0 to 9.


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ArraysDeclaration and Initializaton

Declaration:int ar[10];


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Arrays can be initialized in two ways:


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y




- ar[0] = 5, ar[1]=8, ar[2]=-3;


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y




- ar[0] = 5, ar[1]=8, ar[2]=-3;In this case, the array must declared at an earlier step andshould have at the capability to hold at least 3 values.


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- int ar[] = {5,8,-3};


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- int ar[] = {5,8,-3};In this case, declaration and initialization happens in the same

statement. However, the array has a size 3.


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statement. However, the array has a size 3.In C, arrayscannotbe declared with a variable size. Exampleint var_arr[x];


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statement. However, the array has a size 3.In C, arrayscannotbe declared with a variable size. Exampleint var_arr[x]; THIS IS INCORRECT


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ArraysBasic Facts and Importance of Arrays


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You mustnevertryaccessing an array outsideits bounds.


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If an array has size 100,

you can only use theindices from 0 to 99.


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Use of arrays make it possible to store lots of values in aprogram.(Think of writing a program that takes 100 numbers andarranges them in ascending order. Without arrays, you needto declare 100 separate integers. )


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Use of arrays make it possible to store lots of values in aprogram.(Think of writing a program that takes 100 numbers andarranges them in ascending order. Without arrays, you needto declare 100 separate integers. )

Arrays makes it easier to process the values stored in onearray variable.


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Motivation for using ArrayExample: Computing Maximum I

Maximum numberGet the number of students in class from the user (say n) as input.Get marks of every student and display the maximum.


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1 int main(){

2 int n, a, max=0, i;3 printf("How many students? ");

4 scanf("%d",&n);

5 for(i=0;i max)

9 max = a;

10 }

11 printf("Max mark is %d\n",max);

12 return 0;

13 }


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1 int main(){


4 scanf("%d",&n);

5 for(i=0;i max)9 max = a;

10 }


12 return 0;

13 }

Table : Variable Table

n i a max


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1 int main(){


4 scanf("%d",&n);


10 }


12 return 0;

13 }


n i a max

Before the loop 5 0


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1 int main(){


4 scanf("%d",&n);


10 }


12 return 0;

13 }


n i a max

Before the loop 5 0

After 1st iteration 5 0 4 4


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1 int main(){


4 scanf("%d",&n);


10 }


12 return 0;

13 }


n i a max

Before the loop 5 0

After 1st iteration 5 0 4 4After 2nd iteration 5 1 2 4


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1 int main(){


4 scanf("%d",&n);


10 }


12 return 0;

13 }


n i a max

Before the loop 5 0


After 3rd iteration 5 2 13 13


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1 int main(){


4 scanf("%d",&n);


10 }


12 return 0;

13 }


n i a max

Before the loop 5 0



After 4th iteration 5 3 4 13


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1 int main(){


4 scanf("%d",&n);


10 }


12 return 0;

13 }


n i a max

Before the loop 5 0






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M i i f i A

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Motivation for using ArrayExample: Computing Maximum II

1 int main(){2 int n, a, max=0, i;

3 printf("How many students? ");

4 scanf("%d",&n);

5 for(i=0;i max)

9 max = a;

10 }


12

return 0;13 }


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4 scanf("%d",&n);

5 for(i=0;i max)

9 max = a;

10 }


12

return 0;13 }

The for loop (Line 5 10)


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M ti ti f i A

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4 scanf("%d",&n);

5 for(i=0;i max)

9 max = a;

10 }


12

return 0;13 }


- reads a number,


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4 scanf("%d",&n);

5 for(i=0;i max)

9 max = a;

10 }


12 return 0;

13 }


- reads a number,

- if greater than previousmaximum,


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4 scanf("%d",&n);

5 for(i=0;i max)

9 max = a;

10 }


12 return 0;

13 }


- reads a number,


- it replaces it.


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Motivation for using Array
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4 scanf("%d",&n);

5 for(i=0;i max)

9 max = a;

10 }


12 return 0;

13 }


- reads a number,


- it replaces it.

Note: When the program readsan input from the user, into thevariablea, the previous value

stored in a is lost.


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4 scanf("%d",&n);

5 for(i=0;i max)

9 max = a;

10 }


12 return 0;

13 }


- reads a number,


- it replaces it.

Note: When the program readsan input from the user, into thevariablea, the previous value

stored in a is lost.

Now what if we want to write a program that computes howmany students got the maximum marks?


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Motivation for using ArrayExample: Frequency of Maximum Number I

1 int main(){

2 int n, a, max=0, mark[500], count=0, i;3 printf("How many students? ");

4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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Motivation for using ArrayExample: Frequency of Maximum Number II

1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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ot at o o us g ayExample: Frequency of Maximum Number II

1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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g yExample: Frequency of Maximum Number II

1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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Example: Frequency of Maximum Number II

1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

12 for (i=0; i

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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1 int main(){


4 scanf("%d",&n);

5 for(i=0; i max)

10 max = a;

11 }

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Lab Exam:

12th Feb (Wednesday), 2pm 6pm: Sections A1, A2, A3, A7,A8, A9.13th Feb (Thursday), 2pm 6pm: Sections A4, A5, A6, A10,A11.

Do not use Feedback Form for posting question.

If you have questions, send email.

Programs discussed in class uploaded on Lecture Notes page.


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Factorial of a NumberProblem Statement and C Code
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Problem Statement and C Code

Factorial

The factorial of a non-negativenumber is defined as follows:

0! = 1

n! = n (n 1)! for n 1.

Note factorial is a fast growingfunction.

1 #include

2

3 int main(){

4 int n, f=1, i;

5 printf("Enter number ");6 scanf("%d",&n);

7

8 for (i=1; i

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Datatypes to store integers we have seen int and longint.

The largest datatype in C to store integers is lont long int.

Uses 64 bits. Integers between263 to 263 1.What if we want to manipulate integers beyond this range?

Read the digits of the numbers as characters and store thedigits of the number in an array.


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Handling Very Large IntegersC Program: Reading a Large Number
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C Program: Reading a Large Number

1 int main(){

2 char ch, arr[100];

3 int n=0, i;

4 do{

5 scanf("%c",&ch);

6 arr[n] = ch;

7 n++;

8 } while((ch >= 0) && (ch

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C Program: Reading a Large Number

1 int main(){

2 char ch, arr[100];

3 int n=0, i;

4 do{

5 scanf("%c",&ch);

6 arr[n] = ch;

7 n++;

8 } while((ch >= 0) && (ch

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g g g

1 int main(){

2 char ch;

3 int n=0, i, arr_int[100];

4 do{

5 scanf("%c",&ch);

6 arr_int[n] = ch - 0;

7

n++;8 } while((ch >= 0) && (ch

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g g g

1 int main(){

2 char ch;


4 do{

5 scanf("%c",&ch);


7

n++;8 } while((ch >= 0) && (ch

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g g g

1 int main(){

2 char ch;


4 do{

5 scanf("%c",&ch);


7

n++;8 } while((ch >= 0) && (ch

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1 int main(){

2 char ch;


4 do{

5 scanf("%c",&ch);


7

n++;8 } while((ch >= 0) && (ch

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1 int main(){

2 char ch;3 int n=0, i, arr_int[100], digitsum=0;

4 do{

5 scanf("%c",&ch);


7 n++;

8 } while((ch >= 0) && (ch

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ProblemGenerate all prime numbers up to a given upper limit.

A Greek mathematician named Eratosthenescame up with a

simple idea to solve the above problem.His idea was as follows:

- On a piece of paper, write down all the integers starting from2 till the upper bound.

- Starting from 2 strike off all multiples of 2, except 2.

- Next, find the first number that has not been struck and strikeoff all its multiples, except the number.- Continue until you cannot strike out any more numbers.- The numbers that have not been struck, are PRIMES.


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Generating Prime NumbersSieve of Eratosthenes Example
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2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 5051 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100

Table : Listing all numbers from 2 to 100. Initially unmarked.


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2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 5051 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100

Table : Marking all unmarked multiples of 2 starting from 4.


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2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 5051 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100


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2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 5051 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100




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2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 5051 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100




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2 3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 50

51 52 53 54 55 56 57 58 59 6061 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100

Table : No more numbers can be marked. Algorithm terminates.

Primes up to 100 are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29,31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83,

89, 97.

Raghunath Tewari rtewari@cse iitk ac in ESc101A Arrays

Generating Prime NumbersSieve of Eratosthenes Program

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1 int main(){

2 int comp[10000], n, i, j=2, k;3 comp[0]=0, comp[1]=0;

4 printf("Enter upper bound: ");

5 scanf("%d",&n);

6 for (i=2; i

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1 int main(){

2 int comp[10000], n, i, j=2, k;3 comp[0]=0, comp[1]=0;

4 printf("Enter upper bound: ");

5 scanf("%d",&n);

6 for (i=2; i

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Recap
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Using arrays to store and manipulate very large integers.


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Generating prime numbers using Sieve of Eratosthenesmethod.


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AnnouncementsNew contest on Programming Gymhttp://www2.cse.iitk.ac.in:81/newonj/contests.php?contestID=14


Recap
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AnnouncementsNew contest on Programming Gymhttp://www2.cse.iitk.ac.in:81/newonj/contests.php?contestID=14

Lab Exam timings 2 pm 5 pm

- 12th Feb (Wednesday): Sections A1, A2, A3, A7, A8, A9

- 13th Feb (Thursday): Sections A4, A5, A6, A10, A11


Warm Up ExampleMaximum Element in an Array
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Maximum Element in an Array

Given an array containing n integers, find the maximum number.


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We initially set max to be thefirst element in the array.


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For every number betweenthe second and the lastelement of the array,


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- if the number is largerthan the current max,


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- we assign that number tomax.


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Finally,max will contain themaximum element in thearray.


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Finally,max will contain themaximum element in thearray.

1 max = ar[0];

2 for (i=1; i max)

4 max = ar[i];

5 }


Sorting a List of NumbersProblem Description
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Sorting Problem

Given a list of integers (say in an array), arrange them indescending order.


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Sorting Problem


Example:

- Input: 5 2 9 4 5 8


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Sorting Problem


Example:

- Input: 5 2 9 4 5 8- Output: 9 8 5 5 4 2

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Sorting Problem


Example:

- Input: 5 2 9 4 5 8- Output: 9 8 5 5 4 2

Sorting is an extremely important problem in computerscience.

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Sorting Problem


Example:

- Input: 5 2 9 4 5 8- Output: 9 8 5 5 4 2


A common problem in everyday life.Example:

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Sorting Problem


Example:

- Input: 5 2 9 4 5 8- Output: 9 8 5 5 4 2



- Contact list on your phone.

Ragh nath Te ari t i@ iitk i ESc101A Arrays


S i P bl
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Sorting Problem


Example:

- Input: 5 2 9 4 5 8- Output: 9 8 5 5 4 2



- Contact list on your phone.- Ordering marks before assignment of grades.

Raghunath Tewari

t i@ iitk i ESc101A

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Sorting a List of NumbersSelection Sort: Algorithm
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Raghunath Tewari

t i@ iitk i ESc101A

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1 Select the largest element in your array and swap it with thefirst element of the array.


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2 Consider the subarray from the second element to the last, asyour current array and repeat Step 1.


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2 Consider the subarray from the second element to the last, asyour current array and repeat Step 1.

3 Stop when the array has only one element.


Arrays

Sorting a List of NumbersSelection Sort: Example

5 2 9 4 5 8 Initial Array
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0 5 2 9 4 5 8 Array considered (Max element 9)


Arrays


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y

0 5 2 9 4 5 8 Array considered (Max element 9)9 2 5 4 5 8 After swapping


Arrays


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y




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y



9 8 5 4 5 2 After swapping


Arrays


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2 9 8 5 4 5 2 Array considered (Max element 5)9 8 5 4 5 2 After swapping (stays the same)


Arrays


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Arrays


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9 8 5 5 4 2 After swapping (stays the same)


Arrays


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9 8 5 5 4 2 After swapping (stays the same)

9 8 5 5 4 2 Array is sorted


Arrays

Sorting a List of Numbers
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Arrays

Sorting a List of Numbers

1 int main(){

2 int ar[]={2,6,1,9,2,7,9,-2},
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i, j, n=8, max, temp;3

4 for (i=0; i

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4 for (i=0; i

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i, j, n=8, max, temp;

3

4 for (i=0; i

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i, j, n 8, max, temp;

3

4 for (i=0; i

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i, j, n 8, max, temp;

3

4 for (i=0; i

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3

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3

4 for (i=0; i

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3

4 for (i=0; i

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3

4 for (i=0; i

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4 for (i=0; i

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4 for (i=0; i

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4 for (i=0; i

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i, j, n 8, max, temp;3

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4 for (i=0; i

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, j, , , p;3

4 for (i=0; i

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, j, , , p;3

4 for (i=0; i

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j p3

4 for (i=0; i

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3

4 for (i=0; i

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3

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3

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3

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Dot Product

The dot productof two vectors a= (a1, a2, . . . , an) andb= (b1, b2, . . . , bn) is defined as

a b= a1b1+a2b2+ . . .+anbn.

To compute dot product, the two vectors must have the samesize.


Arrays

Dot Product of Two VectorsC Code

1 #include

2 int main(){

3 int a[100],b[100],size, i, dot_prod=0;4 printf("Enter size of vector: ");
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4 printf( Enter size of vector: );

5 scanf("%d",&size);

6 for (i=0; i

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Arrays

Announcements

Lab Exam Schedule:12th Feb (Wednesday)
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12th Feb (Wednesday)

- A1 CSE Lab, Ground Floor, CSE Building- A2, A3 CC Labs, First Floor, CC Building- A7, A8, A9 New Core Labs, Second Floor, New Core Lab

Building13th Feb (Thursday)

- A4, A5 CC Labs, First Floor, CC Building- A6, A10, A11 New Core Labs, Second Floor, New Core Lab

Building


Arrays

Arrays as Arguments to FunctionsExample: Dot Product using Functions
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Arrays

Arrays as Arguments to FunctionsExample: Dot Product using Functions

1 #include

2 int dot_product(int[], int[], int);

3

4 int dot product(int a[] int b[] int

The function dot product

takes as as argument twointeger arrays a and b and
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4 int dot_product(int a[], int b[], int

size){

5 int sum=0, i;

6 for(i=0;i

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size){

5 int sum=0, i;

6 for(i=0;i

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size){

5 int sum=0, i;

6 for(i=0;i

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_p ( [], [],

size){

5 int sum=0, i;

6 for(i=0;i

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When specifying an array argument to a function, it is notnecessary to give the size.


Arrays

Arrays as Arguments to FunctionsHow Arrays are Passed to Functions

When specifying an array argument to a function, it is not
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When specifying an array argument to a function, it is notnecessary to give the size.Reason: Does not create a copy of the array in the functionbox. It only keeps a copy ofthe name of the array.


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When specifying an array argument to a function, it is notnecessary to give the size.Reason: Does not create a copy of the array in the functionbox. It only keeps a copy ofthe name of the array.

If an array is modified in a function call, the actual array ismodified as well.


Arrays


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p y g y g ,necessary to give the size.Reason: Does not create a copy of the array in the functionbox. It only keeps a copy ofthe name of the array.

If an array is modified in a function call, the actual array ismodified as well.

When we study Pointers in the second half of the course,we will discuss this in more detail.


Arrays

Arrays as Arguments to FunctionsUnderstanding Array Manipulation in Function Calls Example
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Arrays


1 void swap1(int a, int b){

2 int temp;

3 temp = a;4 a = b;

b t
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5 b = temp;

6 } // swapping a and b


Arrays



2 int temp;

3 temp = a;4 a = b;

5 b = temp;

1 void swap2(int ar[]){

2 int temp;

3 temp = ar[0];4 ar[0] = ar[1];

5 ar[1] = temp;
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5 b = temp;


5 ar[1] = temp;

6 } // swapping ar[0] and ar[1]


Arrays



2 int temp;

3 temp = a;4 a = b;

5 b = temp;


2 int temp;

3 temp = ar[0];4 ar[0] = ar[1];

5 ar[1] = temp;
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5 b = temp;


5 ar[1] = temp;


1 int main(){

2 int ar[]={5,2}, a=10, b=15;

3 printf ("a=%d b=%d\n",a,b);

4 swap1(a,b);


6

7 printf ("ar[0]=%d ar[1]=%d\n",ar[0],ar[1]);

8 swap2(ar);9 printf ("ar[0]=%d ar[1]=%d\n",ar[0],ar[1]);

10 return 0;

11 }

Output


Arrays



2 int temp;

3 temp = a;4 a = b;

5 b = temp;


2 int temp;

3 temp = ar[0];4 ar[0] = ar[1];

5 ar[1] = temp;
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5 b = temp;


5 ar[1] = temp;


1 int main(){

2 int ar[]={5,2}, a=10, b=15;


4 swap1(a,b);


6



10 return 0;

11 }

Output

$ ./a.out


Arrays



2 int temp;

3 temp = a;4 a = b;

5 b = temp;


2 int temp;

3 temp = ar[0];4 ar[0] = ar[1];

5 ar[1] = temp;
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5 b temp;


5 ar[1] temp;


1 int main(){

2 int ar[]={5,2}, a=10, b=15;


4 swap1(a,b);


6



10 return 0;

11 }

Output

$ ./a.out

a=10 b=15


Arrays



2 int temp;

3 temp = a;4 a = b;

5 b = temp;


2 int temp;

3 temp = ar[0];4 ar[0] = ar[1];

5 ar[1] = temp;
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5 b temp;


5 ar[1] temp;


1 int main(){

2 int ar[]={5,2}, a=10, b=15;


4 swap1(a,b);


6



10 return 0;

11 }

Output

$ ./a.out

a=10 b=15

a=10 b=15


Arrays



2 int temp;

3 temp = a;4 a = b;

5 b = temp;


2 int temp;

3 temp = ar[0];4 ar[0] = ar[1];

5 ar[1] = temp;
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p;


[ ] p;


1 int main(){

2 int ar[]={5,2}, a=10, b=15;3 printf ("a=%d b=%d\n",a,b);

4 swap1(a,b);


6


8

swap2(ar);9 printf ("ar[0]=%d ar[1]=%d\n",ar[0],ar[1]);

10 return 0;

11 }

Output

$ ./a.out

a=10 b=15

a=10 b=15

ar[0]=5 ar[1]=2


Arrays



2 int temp;

3 temp = a;4 a = b;

5 b = temp;


2 int temp;

3 temp = ar[0];4 ar[0] = ar[1];

5 ar[1] = temp;
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p;


p;


1 int main(){

2 int ar[]={5,2}, a=10, b=15;3 printf ("a=%d b=%d\n",a,b);

4 swap1(a,b);


6


8

swap2(ar);9 printf ("ar[0]=%d ar[1]=%d\n",ar[0],ar[1]);

10 return 0;

11 }

Output

$ ./a.out

a=10 b=15

a=10 b=15

ar[0]=5 ar[1]=2

ar[0]=2 ar[1]=5


Arrays

Arrays as Arguments to FunctionsUnderstanding Array Manipulation in Function Calls
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Arrays


When a basic datatype (such as int, char, float, etc) is

passed to a function,
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Arrays


When a basic datatype (such as int, char, float, etc) is

passed to a function,- a copy of thevalueis created in the memory space for thatfunction
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function,


Arrays


When a basic datatype (such as int, char, float, etc) ispassed to a function,

- a copy of thevalueis created in the memory space for thatfunction,
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function,- after the function completes its execution, the values are lost.


Arrays



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,- after the function completes its execution, the values are lost.

When an array is passed to a function,


Arrays



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,- after the function completes its execution, the values are lost.


- a copy of thename of the arrayis created in the memory spacefor that function,


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- after the function completes its execution, the values are lost.


- a copy of thename of the arrayis created in the memory spacefor that function,- whatever manipulation is done with thisarray name, is

happening to the original array,


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happening to the original array,- after the functions completes its execution, the array might

have potentially changed.


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happening to the original array,- after the functions completes its execution, the array might

have potentially changed.

Note: Name of a variable is NOT THE SAME ASthecontents of that variable.


Arrays

Multi-Dimensional Arrays
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Arrays


Arrays to store higher dimensional data such as matrices.
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Arrays



Declaration:

int mat[3][4];
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Arrays



Declaration:

int mat[3][4];

The cells of the array mat are:
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mat[0][0] mat[0][1] mat[0][2] mat[0][3]

mat[1][0] mat[1][1] mat[1][2] mat[1][3]

mat[2][0] mat[2][1] mat[2][2] mat[2][3]

Note that both indices start at 0.


Arrays



Declaration:

int mat[3][4];


[ ][ ] [ ][ ] [ ][ ] [ ][ ]
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mat[0][0] mat[0][1] mat[0][2] mat[0][3]

mat[1][0] mat[1][1] mat[1][2] mat[1][3]

mat[2][0] mat[2][1] mat[2][2] mat[2][3]


Think of matas an array of arrays.


Arrays



Declaration:

int mat[3][4];


[0][0] [0][1] [0][2] [0][3]
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mat[0][0] mat[0][1] mat[0][2] mat[0][3]

mat[1][0] mat[1][1] mat[1][2] mat[1][3]

mat[2][0] mat[2][1] mat[2][2] mat[2][3]



- The individual elements ofmatare mat[0], mat[1], mat[2],and


Arrays



Declaration:

int mat[3][4];


t[0][0] t[0][1] t[0][2] t[0][3]
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mat[0][0] mat[0][1] mat[0][2] mat[0][3]

mat[1][0] mat[1][1] mat[1][2] mat[1][3]

mat[2][0] mat[2][1] mat[2][2] mat[2][3]



- The individual elements ofmatare mat[0], mat[1], mat[2],and

- each element is an integer array. For example, mat[1] is thearray of integers

mat[1][0], mat[1][1], mat[1][2], mat[1][3]


Arrays

Multi-Dimensional ArraysTranspose of a Matrix: Definition

Transpose of a Matrix

Let m11 m12 . . . m1mm21 m22 . . . m2m
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M=

21 22 2m

......

...mn1 mn2 . . . mnm

be an nm matrix. Then the transpose ofM is the m n matrix defined as

MT =

m11 m21 . . . mn1m12 m22 . . . mn2

......

...m1m m2m . . . mnm

.


Arrays

Multi-Dimensional ArraysTranspose of a Matrix: Definition

Transpose of a Matrix

Let m11 m12 . . . m1mm21 m22 . . . m2m

For example if

5 3 2
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M=

......

...mn1 mn2 . . . mnm

be an nm matrix. Then the transpose ofM is the m n matrix defined as

MT =

m11 m21 . . . mn1m12 m22 . . . mn2

......

...m1m m2m . . . mnm

.

M=

5 3 28 4 1

then,

MT =

5 83 4

2 1

.


Arrays

Multi-Dimensional ArraysTranspose of a Matrix: C Code

1 int main(){

2 int m[100][100], row, col, i, j;

3 printf("Enter number of rows: ");

4

scanf("%d",&row);5 printf("Enter number of columns: ");

6 scanf("%d",&col);

7 for (i=0; i

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8 for (j=0; j

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8 for (j=0; j

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8 for (j=0; j

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8 for (j=0; j

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8 for (j=0; j

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8 for (j=0; j

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Arrays

Recap

Passing arrays as arguments to functions.

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Arrays

Recap

Passing arrays as arguments to functions.In case of the basic datatypes such as int, float, etc, thevalues are copied in the function space.
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p p


Arrays

Recap

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In case of array, only the name is copied.

Example: Dot product, Swapping of elements


Arrays

Recap

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In case of array, only the name is copied.

Example: Dot product, Swapping of elementsMultidimensional Arrays.

Example: Transpose of a matrix.


Arrays

Multi-Dimensional ArraysColumn Average: Problem Description

Computing Column Average

Write a program that implements a function to do the following:- takes as input a two-dimensional array of integers (together

with number of rows and columns of the array),
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- computes the average of each column, and returns theaverages.


Arrays




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For example, if the array is as follows:

M=

5 83 4

2 1

,

then the values returned are


Arrays





h f h l d h
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For example, if the array is as follows:

M=

5 83 4

2 1

,

then the values returned are 3.33 4.33


Arrays

Multi-Dimensional ArraysColumn Average: Returning Multiple Values
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Arrays


Observe that the number of values that we need to return isequal to the number of columns.
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Arrays



When we discussed functions we noted that a function canreturn only one value.
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How do we solve the problem?
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Answer: We exploit the fact that when an array is modifiedin a function, the modification happens in the actual array inthe parent function.


Arrays




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Answer: We exploit the fact that when an array is modifiedin a function, the modification happens in the actual array inthe parent function.

Solution:

- Pass an extra array as an argument to the function.

- This array will store the averages of all the columns.void column_average(int a[][10], int r, int c, float avg[]);


Arrays

Multi-Dimensional ArraysColumn Average: C Code

1 void column_average(int a[][10],int r, int c, float avg[]){

2 int i,j,sum;

3
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4 for (i=0; i

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4 for (i=0; i

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4 for (i=0; i

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4 for (i=0; i

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4 for (i=0; i

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4 for (i=0; i

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9 }

10 int main(){

11 int m[10][10],i,j;12 float avg[10];

13

14 for (i=0;i

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(between 0 and n 1),- else, it displays1.


Arrays

Searching in an ArrayProblem Description

Searching in an Array

Write a program that searches for a given element in an array ofsize n and,

- if the element is found, it displays the index of the element(between 0 and n 1)

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(between 0 and n 1),- else, it displays1.

For example, if the array is{5, 0,2, 8, 3, 8} and element to besearched for

- is 8, then the program displays 3,

- is 10, then the program displays1.


Arrays

Searching in an ArrayC Program

1 int array_search(int arr[], int size, int elt){

2 int i;

3 for (i=0; i

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10 int a1[100], i, n, search;

11 printf("Enter size of array: ");

12 scanf("%d",&n);13 for (i=0; i

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12 scanf("%d",&n);13 for (i=0; i

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12 scanf("%d",&n);13 for (i=0; i

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12 scanf("%d",&n);13 for (i=0; i

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Arrays

Tips for Lab ExamGeneral Instructions

Questions are ordered in increasing order of difficulty.
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Arrays



Read all instructions and the questions carefully.
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Arrays




Approaching a problem:- Make sure your program compiles correctly and gives thecorrect output.
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Arrays





- Dont try to write the entire program in one attempt.
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Arrays





- Dont try to write the entire program in one attempt.- Write short segments of code and keep compiling whenever
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possible to ensure correctness.


Arrays






bl
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- If your program is not doing what it should,


Arrays






ibl
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- If your program is not doing what it should,- insert dummy printf statements to test where it is going

wrong,


Arrays






ibl t t
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wrong,- make a variable table (especially when using loops).


Arrays



Read all instructions and the questions carefully.Approaching a problem:

- Make sure your program compiles correctly and gives thecorrect output.


ibl t t
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- Use functions to divide your program into smaller components.


Arrays






possible to ensure correctness
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- Important: Write comments to explain your code.


Arrays






http://find/

8/12/2019 ESc101 S 06 Arrays

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- Important: Write comments to explain your code.- Give meaningful variable names whenever possible.


Arrays






http://find/

8/12/20

esc101 s 06 arrays

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