Array and its operation in C programming

Familiarization of Array and its operation

1. Array in C

2. Introduction to Arrays An array is used to process a collection of data of the same type Examples: A list of names A list of temperatures Why do we need arrays? Imagine keeping track of 100 test scores or 1000 in memory How would you name all the variables? How would you process each of the variables? Array in C 2 Prepared by : Er. Rhishav Poudyal

3. ARRAYS An array is a collection of elements of the same type that are referenced by a common name . Compared to the basic data type ( int , float & char ) it is an aggregate or derived data type . All the elements of an array occupy a set of contiguous memory locations. Consider the following issue: "We have a list of 1000 students' marks of an integer type. If using the basic data type ( int ), we will declare something like the following…" int  studMark0, studMark1, studMark2, ..., studMark999;

4. ARRAYS Can you imagine how long we have to write the declaration part by using normal variable declaration? int main(void) { int studMark1, studMark2, studMark3, studMark4, … , …, studMark998, stuMark999, studMark1000; … … return 0; }

5. Definition and Initialization Array is defined as the user defined (derived) data type which hold multiple data having same kind of data type. An array is defined using a declaration statement. data_type array_name [size]; allocates memory for size elements subscript of first element is 0 subscript of last element is size-1 size must be a constant 5 Array in C Prepared by : Er. Rhishav Poudyal

6. Definition – Array A collection of objects of the same type stored contiguously in memory under one name May be type of any kind of variable May even be collection of arrays! For ease of access to any member of array For passing to functions as a group 6 Array in C Prepared by : Er. Rhishav Poudyal

7. Initializing Arrays To initialize an array when it is declared The values for the indexed variables are enclosed in braces and separated by commas Example: int children[3] = { 2, 12, 1 }; Is equivalent to: int children[3]; children[0] = 2; children[1] = 12; children[2] = 1; Array in C 7 Prepared by : Er. Rhishav Poudyal

8. One-Dimensional Arrays Suppose, you need to store years of 100 cars. Will you define 100 variables? int y1, y2,…, y100; An array is an indexed data structure to represent several variables having the same data type: int y [ 100 ] ; 8 y[0] y[1] y[2] … y[k-1] y[k] y[k+1] … y[98] y[99] Array in C Prepared by : Er. Rhishav Poudyal

9. Arrays Array Group of consecutive memory locations Same name and type To refer to an element, specify Array name Position number Format: arrayname [ position number ] First element at position n element array named c : c[ 0 ] , c[ 1 ] ... c[ n – 1 ] 9 Array in C Prepared by : Er. Rhishav Poudyal

10. One-Dimensional Arrays (cont’d) An element of an array is accessed using the array name and an index or subscript , for example: y[5] which can be used like a variable In C, the subscripts always start with 0 and increment by 1, so y[5] is the sixth element The name of the array is the address of the first element and the subscript is the offset 10 y[0] y[1] y[2] … y[k-1] y[k] y[k+1] … y[98] y[99] Array in C Prepared by : Er. Rhishav Poudyal

11. Arrays Array elements are like normal variables c[ 0 ] = 3; printf( "%d", c[ 0 ] ); Perform operations in subscript. If x equals 3 c[ 5 - 2 ] == c[ 3 ] == c[ x ] 11 Array in C Prepared by : Er. Rhishav Poudyal

12. Declaring Arrays When declaring arrays, specify Name Type of array Number of elements arrayType arrayName[ numberOfElements ]; Examples: int c[ 10 ]; float myArray[ 3284 ]; Declaring multiple arrays of same type Format similar to regular variables Example: int b[ 100 ], x[ 27 ]; 12 Array in C Prepared by : Er. Rhishav Poudyal

13. Examples (continued) int C[] An array of an unknown number of integers (allowable in a parameter of a function) C[0] , C[1] , …, C [ max-1 ] int D[10][20] An array of ten rows, each of which is an array of twenty integers D[0][0] , D[0][1] , …, D[1][0] , D[1][1] , …, D[9][19] Not used so often as arrays of pointers 13 Array in C Prepared by : Er. Rhishav Poudyal

14. Examples (continued) Initializers int n[ 5 ] = { 1, 2, 3, 4, 5 }; If not enough initializers, rightmost elements become int n[ 5 ] = { 0 } All elements 0 If too many a syntax error is produced syntax error C arrays have no bounds checking If size omitted, initializers determine it int n[ ] = { 1, 2, 3, 4, 5 }; 5 initializers, therefore 5 element array 14 Array in C Prepared by : Er. Rhishav Poudyal

15. Declaring an Array An array, named score, containing five variables of type int can be declared as int score[ 5 ]; This is like declaring 5 variables of type int: score[0], score[1], … , score[4] The value in brackets is called A subscript An index Array in C 15 Prepared by : Er. Rhishav Poudyal

16. Assigning values to an array 16 For loops are often used to assign values to an array Example: int list[5], i; for(i=0; i<5; i++){ list[i] = i; } list[0] list[3] list[4] list[1] list[2] 1 2 3 4 list[0] list[1] list[2] list[3] list[4] OR for(i=0; i<=4 ; i++){ list[i] = i; } Array in C Prepared by : Er. Rhishav Poudyal

17. Assigning values to an array 17 Give a for loop to assign the below values to list int list[5], i; for(i=0; i<5; i++){ list[i] = 4-i; } list[0] list[3] list[4] list[1] list[2] 4 3 2 1 Array in C Prepared by : Er. Rhishav Poudyal

18. Array Element May be used wherever a variable of the same type may be used In an expression (including arguments) On left side of assignment Examples:– A[3] = x + y; x = y – A[3]; z = sin(A[i]) + cos(B[j]); 18 Array in C Prepared by : Er. Rhishav Poudyal

19. Array Elements (continued) Generic form:– ArrayName [ integer-expression ] ArrayName [ integer-expression ] [ integer-expression ] Same type as the underlying type of the array Definition:– Array Index – the expression between the square brackets 19 Array in C Prepared by : Er. Rhishav Poudyal

20. Array Elements (continued) Array elements are commonly used in loops E.g., for( i =0; i < max; i ++) A[ i ] = i * i ; sum = 0; for(j=0; j < max; j++) sum += B[j]; 20 Array in C Prepared by : Er. Rhishav Poudyal

21. Array Initialization int A[5] = {2, 4, 8, 16, 32}; Static or automatic int B[20] = {2, 4, 8, 16, 32}; Unspecified elements are guaranteed to be zero int C[4] = {2, 4, 8, 16, 32}; Error — compiler detects too many initial values int D[5] = {2*n, 4*n, 8*n, 16*n, 32*n}; Automatically only; array initialized to expressions 21 Array in C Prepared by : Er. Rhishav Poudyal

22. Implicit Array Size Determination int days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; Array is created with as many elements as initial values In this case, 12 elements Values must be compile-time constants (for static arrays) Values may be run-time expressions (for automatic arrays) 22 Array in C Prepared by : Er. Rhishav Poudyal

23. Caution! Caution! Caution! It is the programmer’s responsibility to avoid indexing off the end of an array Likely to corrupt data May cause a segmentation fault Could expose system to a security hole! C does NOT check array bounds I.e., whether index points to an element within the array Might be high (beyond the end) or negative (before the array starts) 23 Array in C Prepared by : Er. Rhishav Poudyal

24. Initializing Arrays Arrays can be initialized at the time they are declared . Examples: double taxrate [3] ={0.15, 0.25, 0.3}; char list[5] = {‘h’, ’e’, ’l’, ’l’, ’o’}; double vector[100] = {0.0}; /* assigns zero to all 100 elements */ int s[] = {5,0,-5}; /*the size of s is 3*/ 24 Array in C Prepared by : Er. Rhishav Poudyal

25. Computations on 1-D arrays

26. Find Maximum Find maximum value in data array int data[100], max, i ; for ( i =0; i <100; i ++) scanf (“% d”,&data [ i ]); max = data[0]; for ( i =1; i <100; i ++){ if (data[ i ] > max) max = data[ i ]; } printf ("Max = %d\ n",max ); 26 Array in C Prepared by : Er. Rhishav Poudyal

27. Find average 27 Find average of values in data array int data[100], sum, i , avg ; for ( i =0; i <100; i ++) data[ i ] = rand_int (10,109); sum = 0; for ( i =0; i <100; i ++) { sum = sum + data[ i ]; } avg = (double)sum/100; printf (“ Avg = %lf\n", avg ); Array in C Prepared by : Er. Rhishav Poudyal

28. Number of elements greater than average After finding the average as shown in previous slide, use the following code 28 count = 0; for ( i =0; i <100; i ++) { if (data[ i ] > avg ) count++; } printf (“%d elements are greater than avg ”, count); Array in C Prepared by : Er. Rhishav Poudyal

29. Copy array1 to array2 in reverse order 29 6 3 1 9 7 2 2 1 3 4 5 2 7 9 1 3 6 array1 array2 Array in C Prepared by : Er. Rhishav Poudyal

30. What are Multidimensional Arrays A multidimensional array is treated as an array of arrays. Let a be a k-dimensional array; the elements of a can be accessed using the following syntax: a [ i 1 ] [ i 2 ]…[ i k ] where i 1 , i 2 , ….., i k Array in C 30 Prepared by : Er. Rhishav Poudyal

31. Multidimensional Arrays Applying what we learned about simple arrays to multidimensional array , we get the following: A k-dimensional array can be created with either of the following methods: Using the new operator Using the k-dimensional initializer Array in C 31 Prepared by : Er. Rhishav Poudyal

32. Creating k-dimensional Array Using the new operator new Type [ n1] [n2]…[ nk ] Size of each dimension is n1, n2, …, nk , respectively. All the elements in the array are initialized to default initial values based on the type of the elements Using k-dimensional array initializer { I 1 , I 2 , ...., I k } where each I 1 , I 2 , ...., I k is a (k-1)- dimensional array initializer . Array in C 32 Prepared by : Er. Rhishav Poudyal

33. Examples … Using the new operator, the following example is of creating and initializing a two-dimensional array. double mat1[4 ][5 ] This creates a 4 x 5 two-dimensional array. All elements are initialized to 0.0. Using k-dimensional array initializer , the following example is of creating and initializing a two-dimensional array. int mat2[ ] [ ] = {{1, 2, 3}, {4, 5, 6}}; This creates a 2 x 3 two-dimensional array. The elements are initialized as: mat2[0][0]=1 mat2[1][0]= 4 mat2[0][1]=2 mat2[1][1]= 5 mat2[0][2]=3 mat2[1][2]= 6 Array in C 33 Prepared by : Er. Rhishav Poudyal

34. Two Dimensional Arrays A two dimensional array stores data as a logical collection of rows and columns . Each element of a two-dimensional array has a row position and a column position. To access an element in a two-dimensional array, you must specify the name of the array followed by: a row offset a column offse t Array in C 34 Prepared by : Er. Rhishav Poudyal

35. Declaration and Initialization The declaration of a two-dimensional array requires a row size and a column size . All array elements must be of the same type. Elements accessed by two offsets – a row offset and a column offset. The name of the array holds the address of the first byte of memory Array in C 35 Prepared by : Er. Rhishav Poudyal

36. Example //Declaration int data[2][3]; Memory Snapshot ? ? ? ? ? ? data Array in C 36 Prepared by : Er. Rhishav Poudyal

37. Example //Declaration int data[2][3]; ? ? ? ? ? ? row 0 row 1 col 0 col 1 col 2 row/column form: Array in C 37 Prepared by : Er. Rhishav Poudyal

38. 2D Array Definition Syntax Syntax: data_type identifier [ [ row_size ] ][ column_size ] [ = initialization_list ] ; // row_size and column_size must be integer constants Examples int data[2][5]; //allocates consecutive memory for 10 integer values double t[2][2] = {{3.0,5.0},{2.1,7.2}}; //allocates and initializes Array in C 38 Prepared by : Er. Rhishav Poudyal

39. Initialization Examples int temp [4][3] = {50, 70, 60, 48, 75, 62, 51, 69, 60, 52, 78, 63}; int temp [4][3] = {{50, 70, 60}, {48, 75, 62}, {51, 69, 60}, {52, 78, 63}}; int temp[][3] = {{50, 70, 60}, {48, 75, 62}, {51, 69, 60}, {52, 78, 63}}; int temp [][3] = {50, 70, 60, 48, 75, 62, 51, 69, 60, 52, 78, 63}; Array in C 39 Prepared by : Er. Rhishav Poudyal

40. Example: Input Nested for loops are often used when inputting and assigning values to a two-dimensional array. Nested loops are generally useful for getting around the 2D arrays… //Declaration double table[RSIZE][CSIZE]; for ( int i =0; i <RSIZE; ++ i ) //every row for ( int j=0; j<CSIZE; ++j ) //every col scanf (“% lf”,&table [ i ][j]; Array in C 40 Prepared by : Er. Rhishav Poudyal

41. Example: Assignment //Declaration const int RSIZE(3),CSIZE(2); double v[RSIZE][CSIZE]; for (int i=0; i<RSIZE; ++i) //every row for (int j=0; j<CSIZE; ++j ) //every col v[i][j] = i+j; 1 1 2 2 3 V Array in C 41 Prepared by : Er. Rhishav Poudyal

42. Example: Computations Compute the average value of an array with n rows and m columns. double sum(0), average; for (int i =0; i <n; ++ i ) //every row for (int j=0; j<m; ++j ) //every col sum += array[ i ][j]; average = sum / (n*m); Array in C 42 Prepared by : Er. Rhishav Poudyal

43. Example: Computations Compute the average value of the nth row of a 2D array with r rows and c columns. double sum(0), rowAverage; for (int j=0; j<c; ++j ) //every col sum += array[n][j]; average = sum / c; Array in C 43 Prepared by : Er. Rhishav Poudyal

44. Outputting 2D Arrays Two dimensional arrays are often printed in a row by row format, using nested for statements. When printing the row values of an array, be sure to print: whitespace between the values in a row. a newline character at the end of each row. Array in C 44 Prepared by : Er. Rhishav Poudyal

45. Example: Printing for ( int i =0; i <n; ++ i ) { //every row { for ( int j=0; j<m; ++j ) //every col printf (“% d”, array [ i ][j]); } Array in C 45 Prepared by : Er. Rhishav Poudyal

46. Matrix A matrix is a set of numbers arranged in a rectangular grid with rows and columns. A square matrix has the same number of rows as columns. Row and Column offsets in Matrices are 1-based. 2D Arrays are useful for representing matrices. Array in C 46 Prepared by : Er. Rhishav Poudyal

47. Matrix Computations and Operations The determinant of a matrix is a scalar value used in computing matrix inverses and solving systems of simultaneous equations. The transpose of a matrix is a new matrix in which the rows of the original matrix are the columns of the transpose. Matrices of the same size may be added or subtracted element-by-element. Matrix multiplication (M * N) is defined only when the number of columns of M is equal to the number of rows in N. Result has the size rows(M) x cols(N) Array in C 47 Prepared by : Er. Rhishav Poudyal

48. C program to store temperature of two cities for a week and display it. 48 Array in C Prepared by : Er. Rhishav Poudyal

49. 49 const int CITY = 2; const int WEEK = 7; void main() { int temperature[CITY][WEEK]; for ( int i = 0; i < CITY; ++ i ) { for( int j = 0; j < WEEK; ++j) { printf ("City %d, Day %d: ", i+1, j+1); scanf ("%d", &temperature[ i ][j]); } } printf ("\ nDisplaying values: \n\n"); for ( int i = 0; i < CITY; ++ i ) { for( int j = 0; j < WEEK; ++j) { printf ("City %d, Day %d = %d\n", i+1, j+1, temperature[ i ][j]); } } } Array in C Prepared by : Er. Rhishav Poudyal

50. WAP to find the sum of two matrices of order 2*2 . 50 Array in C Prepared by : Er. Rhishav Poudyal

51. 51 #include < stdio.h > int main() { float a[2][2], b[2][2], c[2][2]; int i , j; printf ("Enter elements of 1st matrix\n"); for( i =0; i <2; ++ i ) for(j=0; j<2; ++j) { printf ("Enter a%d%d : ", i+1, j+1); scanf ("%f", &a[ i ][j]); } printf ("Enter elements of 2nd matrix\n"); for( i =0; i <2; ++ i ) for(j=0; j<2; ++j) { printf ("Enter b%d%d : ", i+1, j+1); scanf ("%f", &b[ i ][j]); } Array in C Prepared by : Er. Rhishav Poudyal

52. 52 // adding corresponding elements of two arrays for( i =0; i <2; ++ i ) for(j=0; j<2; ++j) { c[ i ][j] = a[ i ][j] + b[ i ][j]; } // Displaying the sum printf ("\ nSum Of Matrix:"); for( i =0; i <2; ++ i ) for(j=0; j<2; ++j) { printf ("%.1f\t", c[ i ][j]); if(j==1) printf ("\n"); } return 0; } Array in C Prepared by : Er. Rhishav Poudyal

53. WAP to Find Transpose of a Matrix 53 Array in C Prepared by : Er. Rhishav Poudyal

54. 54 #include < stdio.h > void main() { int a[10][10], transpose[10][10], row, col, i , j; printf ("Enter rows and columns of matrix: "); scanf ("%d %d", &row, &col); printf ("\ nEnter elements of matrix:\n"); for( i =0; i <row; ++ i ) for(j=0; j< col ; ++j) { printf ("Enter element a%d%d : ",i+1, j+1); scanf ("%d", &a[ i ][j]); } Array in C Prepared by : Er. Rhishav Poudyal

55. 55 // Finding the transpose of matrix a for( i =0; i <row; ++ i ) for(j=0; j< col ; ++j) { transpose[j][ i ] = a[ i ][j]; } // Displaying the transpose of matrix a printf ("\ nTranspose of Matrix:\n"); for( i =0; i < col ; ++ i ) for(j=0; j<row; ++j) { printf ("%d ",transpose[ i ][j]); if(j==r-1) printf ("\n\n"); } } Array in C Prepared by : Er. Rhishav Poudyal

56. Program to Multiply Two Matrices 56 Array in C Prepared by : Er. Rhishav Poudyal

57. 57 #include < stdio.h > int main() { int a[10][10], b[10][10], result[10][10], r1, c1, r2, c2, i , j, k; printf ("Enter rows and column for first matrix: "); scanf ("%d %d", &r1, &c1); printf ("Enter rows and column for second matrix: "); scanf ("%d %d",&r2, &c2); // Column of first matrix should be equal to row of second matrix and if (c1 != r2) { printf ("Error! column of first matrix not equal to row of second.\n\n"); } Array in C Prepared by : Er. Rhishav Poudyal

58. 58 // elements of first matrix. printf ("\ nEnter elements of matrix 1:\n"); for( i =0; i <r1; ++ i ) for(j=0; j<c1; ++j) { printf ("Enter elements a%d%d : ",i+1, j+1); scanf ("%d", &a[ i ][j]); } // elements of second matrix. printf ("\ nEnter elements of matrix 2:\n"); for( i =0; i <r2; ++ i ) for(j=0; j<c2; ++j) { printf ("Enter elements b%d%d : ",i+1, j+1); scanf ("% d",&b [ i ][j]); } Array in C Prepared by : Er. Rhishav Poudyal

59. 59 // Initializing all elements of result matrix to 0 for( i =0; i <r1; ++ i ) for(j=0; j<c2; ++j) { result[ i ][j] = 0; } // Multiplying matrices a and b and // storing result in result matrix for( i =0; i <r1; ++ i ) for(j=0; j<c2; ++j) for(k=0; k<c1; ++k) { result[ i ][j]+=a[ i ][k]*b[k][j]; } Array in C Prepared by : Er. Rhishav Poudyal

60. 60 // Displaying the result printf ("\ nOutput Matrix:\n"); for( i =0; i <r1; ++ i ) for(j=0; j<c2; ++j) { printf ("%d ", result[ i ][j]); if(j == c2-1) printf ("\n\n"); } return 0; } Array in C Prepared by : Er. Rhishav Poudyal