Arrays

1. Arrays DKT121: Fundamental of Computer Programming

2. Outline 6.1 Introduction 6.2 Arrays of Data 6.3 Declaration of Array 6.4 Array Initialization 6.5 Operations on Array 6.5 Multidimensional Arrays 6.6 Index out of bound DKT121: Fundamental of Computer Programming

3. What is an Array? • The variables that we have used so far have all common characteristics: • Each variable could only store a single value at a time. • Example: int count, length, baki; double average, jumlah; char selection; • An array is a collection of a fixed number of components wherein all of the components are of the same type DKT121: Fundamental of Computer Programming

4. What is an Array? (Example) • Example: Let us work with a list of five integers: • 5,10, 15, 20, and 25. • Previously we would declare five variables: int num1, num2, num3, num4, num5; • By using array, since they are all of the same data type, we could just write: int num[5]; DKT121: Fundamental of Computer Programming

5. What is an Array? (Example) num • 5 components/elements in this array. • Elements are referred to index. • Element num[2] has index 2 and value 15. num[0] num[1] num[2] num[3] num[4] DKT121: Fundamental of Computer Programming

6. Arrays of Data • Engineering applications usually involves large chunk of data (of common type) • Arrays provide easier and more efficient concept for data storage / management • Arrays are usually processed through loops (processing is very common) • Arrays are accessed by indicating an address or index DKT121: Fundamental of Computer Programming

7. Arrays in C • Arrays can assume any type (including the primitive data types) int, char, string, double, float, etc. • Like any other instances, arrays must be declared before use. DKT121: Fundamental of Computer Programming

8. Declaration of Array • Format: • data_type array_name[int value]; • Example: • int list[5]; • const int Max_List_Size = 10; int hours[Max_List_Size]; • const int SIZE = 100; double amount[SIZE]; • const int Max_List_Size = 6; char alphas[Max_List_Size]; • #define N 10 double b[N]; DKT121: Fundamental of Computer Programming

9. Multiple Instances vs. Array // multiple instance int value1, value2, value3; printf (“Enter first value: “); scanf (“%d”, &value1); printf(“Enter second value: “); scanf(“%d”, &value2); printf (“Enter third value: “); scanf(“%d”, &value3); // process or display // array int valueArray[3]; for(int count=0;count<3;count++) { printf (“Enter value #”); printf (“%d : ”, count+1); scanf (“%d”, &valueArray[count]); } // process or display DKT121: Fundamental of Computer Programming

10. Arrays - Memory Allocation • Arrays are allocated bulk memory • Single reference used for multiple locations • Items are accessed based on index (address) with reference to first item DKT121: Fundamental of Computer Programming

11. Arrays Arithmetic • Operations on arrays are similar to that on basic variables. • sum = num[0] + num[1] + num[2] + num[3]; • kali = 3 * num[1]; • baki= num[3] % 3; • Jumlah= num[1] * num[2]; DKT121: Fundamental of Computer Programming

12. Array Initialization • 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 sales[5] = {12.25, 32.50, 16.90, 23, 45.68}; sales[0]=12.25, sales[1]= 32.50, sales[2]=16.90, sales[3]= 23.00, and sales[4]=45.68; DKT121: Fundamental of Computer Programming

13. Array Initialization (cont…) • Initializers int n[ 5 ] = { 1, 2, 3, 4, 5 }; • If not enough initializers, rightmost elements become 0 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 DKT121: Fundamental of Computer Programming

14. Sample Program Initializes the first 2 elements of the a[]array. All the other elements are then automatically set to zero 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. #include <stdio.h> int main() { int a[3]= {11,22}, b[]={44, 55, 66},i; double x[2],y[10]; printf("a[0]=%2d, a[1]=%2d, a[2]=%2d \n" "b[0]=%2d, b[1]=%2d, b[2]=%2d \n\n", a[0],a[1],a[2],b[0],b[1],b[2]); printf("Please enter two real numbers\n"); scanf("%lf %lf",&x[0], &x[1]); printf("x[0] = %.1lf x[1] = %.1lf\n\n", x[0], x[1]); for (i=0;i<10;i++) { y[i]= i*100.0; printf("y[%1d]=%.2lf\n", i, y[i]); } return 0; } Using a loop to fill all the elements of the y[] array. DKT121: Fundamental of Computer Programming

15. Sample Program(cont…) • Output: a[0]=11, a[1]=22, a[2]= 0 b[0]=44, b[1]=55, b[2]=66 Please enter two real numbers 77.0 88.0 x[0] = 77.0 x[1] = 88.0 y[0]=0.00 y[1]=100.00 y[2]=200.00 y[3]=300.00 y[4]=400.00 y[5]=500.00 y[6]=600.00 y[7]=700.00 y[8]=800.00 y[9]=900.00 DKT121: Fundamental of Computer Programming

16. Array Initialization During Declaration When initializing arrays while declaring them, 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 sales[] = {12.25, 32.50, 16.90, 23, 45.68}; DKT121: Fundamental of Computer Programming

17. A simple example • The program declares and initializes the array y. It uses a for loop with index i to access the successive elements of y. For each loop iteration, the value accessed id added to the variable total which is finally displayed. Note that the loop index i starts from 0 to 4(not from 1 to 5). Also, note that the array size n is declared in the define statement. DKT121: Fundamental of Computer Programming

18. A simple example (cont..) #include<stdio.h> #define n 5 //define number of n in the array void main() { int i, total = 0; //variable declaration int y[n]={9,6,20,5,12}; // array initialization for (i=0;i<n;i++) total = total + y[i]; printf ("\nTotal = %d\n“, total); } DKT121: Fundamental of Computer Programming

19. Notes • 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 with no need to make any other changes to the program, thus making the life of programmer easier. DKT121: Fundamental of Computer Programming

20. Operations on Array • Reading data in an array for (index = 0; index < 10; index++) scanf (“%d”, &sale[index]); • Printing an array for (index = 0; index < 10; index++) printf (“%d ”, sale[index]); DKT121: Fundamental of Computer Programming

21. Parallel Arrays • Two (or more) Arrays are called parallel if their corresponding components hold related information. int studentId[50]; char courseGrade[50]; DKT121: Fundamental of Computer Programming

22. Multi-Dimensional Arrays • 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 DKT121: Fundamental of Computer Programming

23. 2-Dimensional Array (Example) DKT121: Fundamental of Computer Programming

24. Multi-Dimensional Arrays(cont..) • A collection of the same type of data stored in contiguous and increasing memory locations. • Declaration of multi-dimensional array: • int b[2][3] = {51, 52, 53, 54, 55, 56}; array_type array_name Array dimension = 2 two rows three columns first row initial values second row initial values DKT121: Fundamental of Computer Programming

25. Multi-Dimensional Arrays(cont..) • Multi-dimensional array can be initialized directly in the declaration statement. • For example: • int b[2][3] = {51, 52, 53, 54, 55, 56}; which initializes the elements to be b[0][0] = 51 b[0][1] = 52 b[0][2] = 53 b[1][0] = 54 b[1][1] = 55 b[1][2] = 56 * note that C begins its subscripts at 0. The rightmost subscript is incremented first. DKT121: Fundamental of Computer Programming

26. Multi-Dimensional Arrays(cont..) • Also can use braces ({ }) to separate row in 2-dimensional arrays. • For example: • int c [4][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10,11,12}}; • int c [4][3] = {{1, 2}, {4, 5, 6}, {7}, {10,11,12}}; initializes c[0][2], c[2][1] and c[2][2] to be zero • int c [ ][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10,11,12}}; implicitly declares the number of rows to be 4 3 columns 4 rows rows columns DKT121: Fundamental of Computer Programming

27. Notes on Arrays • Arrays enables 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 requires nested loop structure (e.g. 2-dimensional array) DKT121: Fundamental of Computer Programming

28. Index out of bound • Out of bounds is when (index < 0) or (index > arraySize -1) double num [10] num [0], num [1],….. , num [9] DKT121: Fundamental of Computer Programming

29. Index out of bound • In C, no guard against this problem • Does not check whether index value is within range or not • Can result in accessing data of wrong memory location DKT121: Fundamental of Computer Programming

30. How to overcome? • Use defined loops for (i = 0; i < 10; i ++) list [ i ] = 0; DKT121: Fundamental of Computer Programming

31. End Arrays Q & A! DKT121: Fundamental of Computer Programming