PGT 106 C PROGRAMMING Electronic Department Faculty of

PGT 106 – C PROGRAMMING Electronic Department, Faculty of Engineering Technology Universiti Malaysia Perlis Uni. MAP

W 8 – Arrays (13 April 2015) PGT 106 : C PROGRAMMING 2

Outline 1. 2. 3. 4. 5. 6. 7. Introduction Arrays of Data Array Declaration Array Initialization Operations on Array Multidimensional Arrays Index out of bound PGT 106 : C PROGRAMMING 3

What is an Array? n An array is a collection/group of a fixed number of components wherein all of the components are of the same type referred to a same name Same data type PGT 106 : C PROGRAMMING 4

What is an Array? (Example) n Example: 5, 10, 15, 20, and 25. n Previously we would declare five variables: int i. Num 1, i. Num 2, i. Num 3, i. Num 4, i. Num 5; n By using array, int ai. Num[5]; PGT 106 : C PROGRAMMING 5

What is an Array? (Example) ai. Num 5 n 5 components or elements n Elements are referred to index. n Element ai. Num[2] has index 2 and value 15. ai. Num[0] 10 ai. Num[1] 15 ai. Num[2] 20 ai. Num[3] 25 ai. Num[4] PGT 106 : C PROGRAMMING 6

Arrays of Data n n Engineering applications usually involve large chunk of data (of common type) Arrays provide easy and efficient concept for data storage or management Arrays are usually processed through loops (processing is very common) Arrays are accessed by indicating an address or index/subscript PGT 106 : C PROGRAMMING 7

Arrays in C n n Arrays can take any type (including the primitive data types) int, char, string, double, float, etc. Like any other instances, arrays must be declared before use. PGT 106 : C PROGRAMMING 8

Array Declaration n Format: n n data_type array_name [int value]; int ai. List[5]; n const int Max_Size = 10; int ai. Hours[Max_Size]; n const int Max_List_Size = 6; char ac. Alp[Max_List_Size]; #define N 10 double ad. B[N]; const int SIZE = 100; double ad. Amount[SIZE]; PGT 106 : C PROGRAMMING 9

Multiple Instances vs. Array // multiple instance int i. Value 1, i. Value 2, i. Value 3, i. Value 4, i. Value 5; printf (“Enter fourth value: “); scanf(“%d”, &i. Value 4) printf (“Enter first value: “); scanf (“%d”, &i. Value 1); printf (“Enter fifth value: “); scanf(“%d”, &i. Value 5) printf(“Enter second value: “); scanf(“%d”, &i. Value 2); printf (“Enter third value: “); scanf(“%d”, &i. Value 3); PGT 106 : C PROGRAMMING 10

// array int ai. Value[3]; for(int i. Count=0; i. Count<3; i. Count++) { printf (“Enter value : ”); printf (“%d : ”, i. Count+1); scanf (“%d”, &ai. Value[i. Count]); } Uni. MAP Sem II 09/10 PGT 106 : C PROGRAMMING 11

Arrays - Memory Allocation n Arrays are allocated bulk memory Single reference used for multiple locations Items are accessed based on index (address) with reference to first item int ai. Value[8]; index ai. Value[0]=23; 0 23 ai. Value[1]=56; 1 56 ai. Value[2]=100; 2 100 ai. Value[3]=0; 3 0 ai. Value[4]=12; 4 12 ai. Value[5]=234; 5 234 ai. Value[6]=666; 6 666 ai. Value[7]=4; 7 4 PGT 106 : C PROGRAMMING 12

Arrays Arithmetic n n n Operations on arrays are similar to that on basic variables. i. Sum = ai. Num[0] + ai. Num[1] + ai. Num[2] + ai. Num[3]; i. Mult = 3 * ai. Num[1]; i. Remainder = ai. Num[3] % 3; i. Total = ai. Num[1] + ai. Num[2]; PGT 106 : C PROGRAMMING 13

Array Initialization n n Arrays can be initialized directly, but assignments are done using loops Like any other simple variable, arrays can also be initialized while they are being declared. double ad. Sales[5] = {12. 25, 32. 50, 16. 90, 23, 45. 68}; ad. Sales[0]=12. 25, ad. Sales[1]=32. 50, ad. Sales[2]=16. 90, ad. Sales[3]=23. 00, ad. Sales[4]=45. 68; PGT 106 : C PROGRAMMING 14

Array Initialization (cont…) n Initializers: n If not enough initializers, rightmost element becomes 0 int ai. N[ 7 ] = { 1, 2, 3, 4, 5 }; => ai. N[5] = ai. N[6] = 0 n All elements = 0 int ai. N[ 5 ] = { 0 } ; ▪ If size is omitted, initializers determine the size int ai. N[ ] = { 1, 2, 3, 4, 5 }; 5 initializers, therefore 5 element array PGT 106 : C PROGRAMMING 15

Sample Program #include <stdio. h> int main() { Initializes the first 2 elements of the ai. A[]array. All the other elements are then automatically set to zero int ai. A[3]= {11, 22}, ai. B[]={44, 55, 66}, i. Loop; double ad. X[2], ad. Y[10]; Because no array size is given (the brackets are empty) and three values are given in braces, the array is automatically declared to have a size of 3 with the value shown being the initial element values. printf(“ai. A[0]=%2 d, ai. A[1]=%2 d, ai. A[2]=%2 d n" “ai. B[0]=%2 d, ai. B[1]=%2 d, ai. B[2]=%2 d nn", ai. A[0], ai. A[1], ai. A[2], ai. B[0], ai. B[1], ai. B[2]); printf("Please enter two real numbersn"); scanf("%lf %lf", &ad. X[0], &ad. X[1]); printf(“ad. X[0] = %. 1 lf ad. X[1] = %. 1 lfnn", ad. X[0], ad. X[1]); for (i. Loop=0; i. Loop<10; i. Loop++) { ad. Y[i. Loop]= i. Loop*100. 0; printf(“ad. Y[%1 d]=%. 2 lfn", i. Loop, ad. Y[i. Loop]); } return 0; } PGT 106 : C PROGRAMMING Using a loop to fill all the elements of the ad. Y[] array. 16

Sample Program n Output: ai. A[0]=11, ai. A[1]=22, ai. A[2]= 0 ai. B[0]=44, ai. B[1]=55, ai. B[2]=66 Please enter two real numbers 77. 0 88. 0 ad. X[0] = 77. 0 ad. X[1] = 88. 0 ad. Y[0]=0. 00 ad. Y[1]=100. 00 ad. Y[2]=200. 00 ad. Y[3]=300. 00 ad. Y[4]=400. 00 ad. Y[5]=500. 00 ad. Y[6]=600. 00 ad. Y[7]=700. 00 ad. Y[8]=800. 00 ad. Y[9]=900. 00 PGT 106 : C PROGRAMMING 17

Array Initialization During Declaration n n When declaring and initializing arrays, it is not necessary to specify the size of the array. The size of the array is determined by the number of initial values in the braces. double ad. Sales[] = {12. 25, 32. 50, 16. 90, 23, 45. 68}; PGT 106 : C PROGRAMMING 18

A simple example n The program declares and initializes the array ai. Y. It uses a ‘for’ loop with index i. Loop to access the successive elements of ai. Y. For each loop iteration, the value accessed is added to the variable i. Total which is finally displayed. Note that the loop index i. Loop starts from 0 to 4 (not from 1 to 5). Also, note that the array size n is declared in the define statement. PGT 106 : C PROGRAMMING 19

A simple example (cont. . ) #include<stdio. h> #define n 5 // define number of n in the array int main() { int i. Loop, i. Total = 0; int ai. Y[n]={9, 6, 20, 5, 12}; // variable declaration // array declaration and // initialization for (i. Loop=0; i. Loop<n; i. Loop++) i. Total = i. Total + ai. Y[i. Loop]; printf ("n. Total = %dn”, i. Total); } PGT 106 : C PROGRAMMING 20

Notes n The defined constants, #define is used to ease any future amendments of the codes, for instance, if the array is to be widen to an n of 10 instead of 5, it would be adequate by modifying the line: #define n 5 #define n 10 there is no need to make any other changes to the program, thus making the life of programmer easier. PGT 106 : C PROGRAMMING 21

Operations on Array Reading data in an array for (i. Index = 0; i. Index < 10; i. Index++) scanf (“%d”, &ai. Sale[i. Index]); n Printing an array for (i. Index = 0; i. Index < 10; i. Index++) printf (“%d ”, ai. Sale[i. Index]); n PGT 106 : C PROGRAMMING 22

Parallel Arrays n Two (or more) arrays are called parallel if their corresponding components hold related information. int ai. Student. Id[50]; char ac. Student. Grade[50]; PGT 106 : C PROGRAMMING 23

Multi-Dimensional Arrays n n Arrays can have multiple dimensions Most used is the 2 -dimensional array (for matrix implementation) Actual implementation is a single array (segmented) Nested loop structure usually used to access items PGT 106 : C PROGRAMMING 24

2 -Dimensional Array (Example) int ai. Value[4][2]; ai. Value[2][1]=5; index ai. Value Row 0 Column 0 1 0 Row 3 1 2 3 4 1 2 Row 1 0 5 5 5 6 7 Address Resolution = Row*(Max. Col) + Col PGT 106 : C PROGRAMMING 25

Multi-Dimensional Arrays (cont. . ) n n A collection of the same type of data stored in contiguous and increasing memory locations. Declaration of multi-dimensional array: array_type n array_name Array dimension = 2 int ai. B[2][3] = {51, 52, 53, 54, 55, 56}; two rows three columns first row initial values PGT 106 : C PROGRAMMING second row initial values 26

Multi-Dimensional Arrays (cont. . ) n n Multi-dimensional array can be initialized directly in the declaration statement. For example: int ai. B[2][3] = {51, 52, 53, 54, 55, 56}; which initializes the elements to be ai. B[0][0] = 51 ai. B[0][1] = 52 ai. B[0][2] = 53 ai. B[1][0] = 54 ai. B[1][1] = 55 ai. B[1][2] = 56 * note that C begins its subscripts at 0. The rightmost subscript is incremented first. n PGT 106 : C PROGRAMMING 27

Multi-Dimensional Arrays (cont. . ) n n can use braces ({ }) to separate rows in 2 -dimensional arrays. 3 columns For example: n n n int ai. C [4][3] = {{1, 2, 3}, {4, 5, 6}, rows {7, 8, 9}, 4 rows columns {10, 11, 12}}; int ai. C [4][3] = {{1, 2}, {4, 5, 6}, {7}, {10, 11, 12}}; initializes ai. C[0][2], ai. C[2][1] and ai. C[2][2] to be zero int ai. C [ ][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, 12}}; implicitly declares the number of rows to be 4 PGT 106 : C PROGRAMMING 28

Notes on Arrays n n Arrays enable better and easier data management system Closely related to loops Indexing is zero-based (0 to n-1 for an array with n locations) Multi-dimensional arrays require nested loop structure (e. g. 2 -dimensional array) PGT 106 : C PROGRAMMING 29

Index out of bounds n n ‘Out of bounds’ is when (index < 0) or (index > array. Size - 1) It is a run-time error, happens when an index is outside the valid boundaries of the array. Example: int ai. A[10]; int i. X = 10 ai. A[9] = 3 ; //ok ai. A[i. X] = 4 ; //10 is not within the range 0. . 9 PGT 106 : C PROGRAMMING 30

Index out of bound n In C, no guard against this problem n n Does not check whether index value is within range or not Can result in accessing data of wrong memory location PGT 106 : C PROGRAMMING 31

How to overcome? n Use defined loops for (i. Loop = 0; i. Loop < 10; i. Loop ++) ai. List [ i. Loop ] = 0; PGT 106 : C PROGRAMMING 32

End – Arrays (1) Q & A! PGT 106 : C PROGRAMMING 33