NCS 301 DATA STRUCTURE USING C

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1 NCS 301 DATA STRUCTURE USING C Unit-1 Part-3 Arrays Hammad Mashkoor Lari Assistant Professor Allenhouse Institute of Technology Introduction Array is a contiguous memory of homogeneous elements. Arrays can store multiple values which can be referenced by a single name Array name is actually a pointer to the first location of memory block allocated to name of array. No bound checking concept for arrays in C. Subject Notes by Hammad Lari 1

2 One dimensional Array One subscript specification is needed Syntax:- Datatype var_name [Expression]; //subscript should be a integer value Example:- Int num[7]; Index Num[0] 22 Num[1] 30 Num[2] 2 Data Size = (upper bound lower bound ) + 1 Size of array num=(6-0)+1=7 Size in bytes=size of array X size of (base type ) Size in bytes=7 X 2=14 Num[3] 5 Num[4] 76 Num[5] 8 Num[6] 34 Initialization One Dimensional Array ANSI C allows automatic array variables to be initialized in declarations by constant initializers. The initializers are specified within braces and separated by commas. Example: Int ex[10]= 12, 23, 9, 17, 16, 49 ; Char word[10]= h, e, l, l, o, \0 ; If there are not enough initializers for whole array the remaining elements of array are initialized to zero. Note:-initializations are not assignment statements, they are declarations that allocate and initialize memory. Subject Notes by Hammad Lari 2

3 Accessing One Dimensional Array Individual elements of array can be accessed using following syntax: Array_name[index or subscript]; Example: Num[1]=90; Program: Int a[10],i; For (i=0;i<=9;i++) Scanf( %d,&a[i]); For(i=0;i<=9;i++) Printf( %d,a[i]); Implementation of One Dimensional Array in memory Address of a particular element in a 1-D array is given by relation: No of required Address of element a[k]=b+w*k element in array(index) Example: Base address B=2000 and each element of array occupies 4 bytes then 5 th element of 1D array will be: Size of each element of array Address of element a[5]= *5= = 2020 Subject Notes by Hammad Lari 3

4 Passing arrays to function Arrays like other simple variables can be passed to function. Arrays are by default passed to function by call by reference method because array name is itself a pointer to the first memory location of the array. But we can also pass individual array elements through call by value method. Program: For (i=0;i<=9;i++) Scanf( %d,&a[i]); Sum=funarray(a,9); Printf( %d,sum); Int funarray(int p[],int n) Int s=0,i=0; For(i=0;i<=n-1;i++) S=s+p[i]; Return s; Insertion in 1D Insertion can be done in two ways 1. Insertion at end of array(easily if space enough to accommodate) 2. Insertion at required position-elements must be moved downwards to new location. i v a[0] 1 a[1] 5 a[2] 7 a[3] 6 a[4] 22 a[5] 90 a[6] 0 a[7] 0 a[8] 0 a[9] 0 Position for 20 i v a[0] 1 a[1] 5 a[2] 7 a[3] 6 a[4] a[5] 22 a[6] 90 a[7] 0 a[8] 0 a[9] 0 i v a[0] 1 a[1] 5 a[2] 7 a[3] 6 a[4] 20 a[5] 22 a[6] 90 a[7] 0 a[8] 0 a[9] 0 Subject Notes by Hammad Lari 4

5 Algorithm 1. [Initialize the value of i] set i=len 2. Repeat for i=len down to pos 1. [shift elements down by 1 position] 2. Set a[i+1]=a[i] 3. [end of loop] 3. [insert element at required position] 1. Set a[pos]=num 4. [reset len] set len=len Display the new list of array 6. End a= linear array num= number len= total no of elements pos= position at which num will be inserted Delete from 1D Deleting an element at end of array present no difficulty Deleting element somewhere in middle of array would require to shift all elements to fill the space emptied. i v a[0] 15 a[1] 7 a[2] 20 a[3] 13 a[4] 66 a[5] 90 a[6] 5 a[7] 10 a[8] 50 a[9] 8 i v a[0] 15 a[1] 7 a[2] 20 a[3] 13 a[4] 66 a[5] a[6] 5 a[7] 10 a[8] 50 a[9] 8 i v a[0] 15 a[1] 7 a[2] 20 a[3] 13 a[4] 66 a[5] 5 a[6] 10 a[7] 50 a[8] 8 a[9] Subject Notes by Hammad Lari 5

6 Algorithm 1. Set item= a[pos] 2. Repeat for j=pos to n-1 1. [shift elements 1 position upward] 2. Set a[j]=a[j+1] 3. [end of loop] 4. reset n=n-1 3. Display the new list of array 4. End Traversing of Array It means access to all elements of array. Algorithm 1. Let LB be the lower bound and UB be the upper bound of linear array a. 2. [initialize counter] set i at lower bound LB 3. Repeat for i=lb to UB 1. visit element] display a[i] 2. [End of loop] 4. Exit Subject Notes by Hammad Lari 6

7 Merging two Arrays Combining elements of two arrays to form a new array. First copy all elements of one array into a third empty array and then copy all elements of other array into third array. If sorting is needed you can sort resultant array or sort during merging(its more efficient). i v Array c Array b c[0] 10 Array a i v c[1] 14 i v b[0] 10 c[2] 16 a[0] 10 b[1] 17 c[3] 17 a[1] 17 b[2] 20 c[4] 19 a[2] 20 b[3] 25 c[5] 20 a[3] 25 c[6] 25 a[4] 50 c[7] 30 a[5] 100 c[8] 50 c[9] 100 Algorithm 1. Create three arrays a1,a2,a3. 2. Enter the element p and q in ascending order in a1,a2. 3. Initialize m and n (lower bounds to 0) 4. Check if (a1[m]-a2[n] [assign elements of a1 to a3] a3[c]=a1[m++) Set c=c+1 Else [assign elements of a2 to a3] a3[c]=a2[n++] Set c=c+1 [End of If] 5. Assign remaining elements of a1,a2 and a3 6. Display elements of array 3 7. End Subject Notes by Hammad Lari 7

8 Multi Dimensional arrays [0][0] [0][1] [0][2] Int int_array[10]; Int int_array2d[10][10]; Initialization a 2D Array Int array2d[3][3]=1,2,3,4,5,6,7,8,9; Initialization a 3D Array Int array3d[3][3][3]= 1,2,3 4,5,6 7,8,9 10,11,12 13,14,15 16,17,18 19,20,21 22,23,24 25,26,27 ; [1][0] [1][1] [1][2] [2][0] [2][1] [2][2] Array3d[1][2][0]=16; Why? 1-second grid(first grid will be 0) 2-third row 0-first element of that row Implementation of a 2d Array A 2d array can be implemented in a P.L in 2 ways:- 1. Row major implementation 2. Column major implementation Row major implementation Linearization technique(elements of array are reader from keyboard row wise i.e. The complete first row is stored then the complete second row is stored and so on). Example:- a00 a01 a02 a10 a11 a12 a20 a21 a22 Row1 Row2 Row3 Actual Physical Storage vs Matrix form is logical representation of array Subject Notes by Hammad Lari 8

9 Address of elements in Row major Address of element a[i][j]=b +W (n ( i - L1) + ( j - L2)) L1-lower bound of row L2-lower bound of column Example A 2d array defined as a[4..7,-1 3] requires 2 bytes of storage space.calculate address of element at location a[6][2].given base address is 100. Solution Base address B=100 size W=2 bytes L1=4 L2=-1 U1=7 U2=3 i=6,j=2 Base address Size of each array element No of columns n=u2-l2+1= 3-(-1)+1=5 Address of a[6][2] = 100+2(5(6-4)+(2-(-1))) Number of columns(u2-l2) =100+2(5*2+3)= = 126 Column major implementation The complete first column is stored then the complete second column is stored and so on). Example:- a00 a01 a02 a10 a11 a12 a20 a21 a22 Column1 Column 2 Column 3 Address of element in Row Column major Major implementation implementation Address of element a[i][j]= B + W (m (j L2) + ( i L1)) Where m is number of rows (U1-L1) Example:-a[-20 20,10 35] requires 1 bytes of storage.b=500.find a[0][30] U1-L1+1=20-(-20)+1=41 Address of a[0][30]=500+1(41(30-10)+(0-(-20))) =500+1(41*20+20)=500+1(840)=1340 Subject Notes by Hammad Lari 9

10 Pointers and 1D Arrays Pointer along with 1D can be used either to access a single element or it can also be used to access the whole array. int ar[5], *ip; ar[0] ar[1] ar[2] ar[3] ar[4] ip=6; int ar[5], *ip; //wrong in C ip=&ar[3];//&--address of &-takes address of an object Ip &ar[3] *-the thing pointed to by the pointer &1.5-error(constants don t have addresses) *p=0;//writes zero into thing pointed to by p *p+=1;//adds one to where p points ar[0] ar[1] ar[2] ar[3] ar[4] Program to display 1D array elements Using pointers Without pointers Int *ptr,i; Int I; Int num[]=10,20,30,40,50,60; Int num[]=10,20,30,40,50,60; i=0; i=0; Ptr=&a[0]; While(i<=5) While(i<=5) Printf( Address=%u,&num[i]); Printf( Address=%u,ptr); Printf( element=%d,num[i]); Printf( element=%d,*ptr); i++; i++; Ptr++; Subject Notes by Hammad Lari 10

11 Program to display 2D array elements Using pointers Int *ptr,i,j; Int a[3][2]=100,200,300,400,500,600; Ptr=&a[0][0]; for(i=0;i<=2;i++) Printf( \n ); for(j=0;j<=1;j++) Printf( %d\t,*ptr); Ptr++; Array of Pointers Array of pointers refer to homogeneous collection of pointers. int *ptr[50]; int a[20],b[30],c[10]; Int *ptr[50]; Ptr[0]=&a[0]; Ptr[20]=&b[0]; Ptr[40]=&c[0]; Program Char *ptr[3]; Ptr[0]= hello ; Ptr[1]= how ; Ptr[2]= home ; Printf( %s%s%s,ptr[0],ptr[1],ptr[2]); Subject Notes by Hammad Lari 11

12 Array of Structures Struct employee Int number; Char sex; Int salary; ; Memory space for 3 objects employee data[3]=146, m,1000,200, f,5000,250, m,10000; Practice Problems 1. Wap to evaluate average of 5 numbers 2. Wap to find whether given prime number is palindrome or not. 3. Wap for addition of two matrix. 4. Wap for multiplication of two matrix. 5. Wap for transpose of a matrix 6. Wap to find highest and lowest element in an array 7. Wap to determine if matrix is symmetrical(a=a ). 8. Wap to combine two strings 9. Wap to compare two string 10. Wap to count number of vowels and digits in a given string. 11. Wap to check whether a string is palindrome or not. Subject Notes by Hammad Lari 12

13 Class Website Subject Notes by Hammad Lari 13

An array is a collection of similar elements that is all the elements in an array should have same data type. This means that an array can store

An array is a collection of similar elements that is all the elements in an array should have same data type. This means that an array can store either all integers, all floating point numbers, all characters,