Lecture 7 – Arrays (1)

1. Lecture 7 – Arrays (1) EKT120 : Computer Programming

2. Outline 1. Introduction 2. Arrays of Data 3. Array Declaration 4. Array Initialization 5. Operations on Array 6. Multidimensional Arrays 7. Index out of bound EKT120 : 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 iCount, iLength, iNum; double dAverage, dTotal; char cSelection, cChoice; • An array is a collection of a fixed number of components wherein all of the components are of the same type EKT120 : 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 iNum1, iNum2, iNum3, iNum4, iNum5; • By using array, since they are all of the same data type, we could just write: int aiNum[5]; EKT120 : Computer Programming

5. What is an Array? (Example) aiNum • 5 components or elements in this array. • Elements are referred to index. • Element aiNum[2] has index 2 and value 15. aiNum[0] aiNum[1] aiNum[2] aiNum[3] aiNum[4] EKT120 : Computer Programming

6. Arrays of Data • 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 EKT120 : 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. EKT120 : Computer Programming

8. Array Declaration • Format: • data_type array_name[int value]; • Example: • int aiList[5]; • const int Max_List_Size = 10; int aiHours[Max_List_Size]; • const int SIZE = 100; double adAmount[SIZE]; • const int Max_List_Size = 6; char acAlphas[Max_List_Size]; • #define N 10 double adB[N]; EKT120 : Computer Programming

9. Multiple Instances vs. Array // multiple instance int iValue1, iValue2, iValue3; printf (“Enter first value: “); scanf (“%d”, &iValue1); printf(“Enter second value: “); scanf(“%d”, &iValue2); printf (“Enter third value: “); scanf(“%d”, &iValue3); // process or display // array int aiValue[3]; for(int iCount=0; iCount<3; iCount++) { printf (“Enter value : ”); printf (“%d : ”, iCount+1); scanf (“%d”, &aiValue[iCount]); } // process or display EKT120 : 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 int aiValue[8]; aiValue[0]=23; aiValue[1]=56; aiValue[2]=100; aiValue[3]=0; aiValue[4]=12; aiValue[5]=234; aiValue[6]=666; aiValue[7]=4; index aiValue 0 1 2 3 4 5 6 7 EKT120 : Computer Programming

11. Arrays Arithmetic • Operations on arrays are similar to that on basic variables. • iSum = aiNum[0] + aiNum[1] + aiNum[2] + aiNum[3]; • iMult = 3 * aiNum[1]; • iRemainder = aiNum[3] % 3; • iTotal = aiNum[1] * aiNum[2]; EKT120 : 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 adSales[5] = {12.25, 32.50, 16.90, 23, 45.68}; adSales[0]=12.25, adSales[1]=32.50, adSales[2]=16.90, adSales[3]=23.00, adSales[4]=45.68; EKT120 : Computer Programming

13. Array Initialization (cont…) • Initializers: • If not enough initializers, rightmost element becomes 0 int aiN[ 7 ] = { 1, 2, 3, 4, 5 }; => aiN[5] = aiN[6] = 0 • All elements = 0 int aiN[ 5 ] = { 0 }; ▪ If size is omitted, initializers determine the size int aiN[ ] = { 1, 2, 3, 4, 5 }; 5 initializers, therefore 5 element array EKT120 : Computer Programming

14. Sample Program Initializes the first 2 elements of the aiA[]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 aiA[3]= {11,22}, aiB[]={44, 55, 66},iLoop; double adX[2],adY[10]; printf(“aiA[0]=%2d, aiA[1]=%2d, aiA[2]=%2d \n" “aiB[0]=%2d, aiB[1]=%2d, aiB[2]=%2d \n\n", aiA[0],aiA[1],aiA[2],aiB[0],aiB[1],aiB[2]); printf("Please enter two real numbers\n"); scanf("%lf %lf",&adX[0], &adX[1]); printf(“adX[0] = %.1lf adX[1] = %.1lf\n\n", adX[0], adX[1]); for (iLoop=0;iLoop<10;iLoop++) { adY[iLoop]= iLoop*100.0; printf(“adY[%1d]=%.2lf\n", iLoop, adY[i]); } return 0; } Using a loop to fill all the elements of the adY[] array. EKT120 : Computer Programming

15. Sample Program • Output: aiA[0]=11, aiA[1]=22, aiA[2]= 0 aiB[0]=44, aiB[1]=55, aiB[2]=66 Please enter two real numbers 77.0 88.0 adX[0] = 77.0 adX[1] = 88.0 adY[0]=0.00 adY[1]=100.00 adY[2]=200.00 adY[3]=300.00 adY[4]=400.00 adY[5]=500.00 adY[6]=600.00 adY[7]=700.00 adY[8]=800.00 adY[9]=900.00 EKT120 : Computer Programming

16. Array Initialization During Declaration • 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 adSales[] = {12.25, 32.50, 16.90, 23, 45.68}; EKT120 : Computer Programming

17. A simple example • The program declares and initializes the array aiY. It uses a ‘for’ loop with index iLoop to access the successive elements of aiY. For each loop iteration, the value accessed id is added to the variable iTotal which is finally displayed. Note that the loop index iLoop starts from 0 to 4 (not from 1 to 5). Also, note that the array size n is declared in the define statement. EKT120 : Computer Programming

18. A simple example (cont..) #include<stdio.h> #define n 5 // define number of n in the array void main() { int iLoop, iTotal = 0; // variable declaration int aiY[n]={9,6,20,5,12}; // array declaration and // initialization for (iLoop=0;iLoop<n;iLoop++) iTotal = iTotal + aiY[i]; printf ("\nTotal = %d\n”, iTotal); } EKT120 : 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 there is no need to make any other changes to the program, thus making the life of programmer easier. EKT120 : Computer Programming

20. Operations on Array • Reading data in an array for (iIndex = 0; iIndex < 10; iIndex++) scanf (“%d”, &aiSale[iIndex]); • Printing an array for (iIndex = 0; iIndex < 10; iIndex++) printf (“%d ”, aiSale[iIndex]); EKT120 : Computer Programming

21. Parallel Arrays • Two (or more) arrays are called parallel if their corresponding components hold related information. int aiStudentId[50]; char acStudentGrade[50]; EKT120 : 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 EKT120 : Computer Programming

23. 2-Dimensional Array (Example) int aiValue[4][2]; aiValue[2][1]=5; index aiValue 0 1 2 3 4 5 6 7 Row 0 Row 1 Column 0 1 0 1 2 3 Row Address Resolution = Row*(MaxCol) + Col EKT120 : 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 aiB[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 EKT120 : Computer Programming

25. Multi-Dimensional Arrays (cont..) • Multi-dimensional array can be initialized directly in the declaration statement. • For example: • int aiB[2][3] = {51, 52, 53, 54, 55, 56}; which initializes the elements to be aiB[0][0] = 51 aiB[0][1] = 52 aiB[0][2] = 53 aiB[1][0] = 54 aiB[1][1] = 55 aiB[1][2] = 56 * note that C begins its subscripts at 0. The rightmost subscript is incremented first. EKT120 : Computer Programming

26. Multi-Dimensional Arrays (cont..) • can use braces ({ }) to separate rows in 2-dimensional arrays. • For example: • int aiC [4][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10,11,12}}; • int aiC [4][3] = {{1, 2}, {4, 5, 6}, {7}, {10,11,12}}; initializes aiC[0][2], aiC[2][1] and aiC[2][2] to be zero • int aiC [ ][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 EKT120 : Computer Programming

27. Notes on Arrays • 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) EKT120 : Computer Programming

28. Index out of bounds • ‘Out of bounds’ is when (index < 0) or (index > arraySize - 1) • It is a run-time error, happens when an index is outside the valid boundaries of the array. Example: int aiA[10]; int iX = 10 aiA[9] = 3 ; //ok aiA[iX] = 4 ; //10 is not within the range 0..9 EKT120 : 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 EKT120 : Computer Programming

30. How to overcome? • Use defined loops for (iLoop = 0; iLoop < 10; iLoop ++) aiList [ iLoop ] = 0; EKT120 : Computer Programming

31. End – Arrays (1) Q & A! EKT120 : Computer Programming