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Lecture 7 – Arrays (1)

Lecture 7 – Arrays (1). 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. What is an Array?.

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Lecture 7 – Arrays (1)

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  1. Lecture 7 – Arrays (1) PGT 106 : C 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 PGT 106 : C PROGRAMMING

  3. What is an Array? • 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 Same name PGT 106 : C PROGRAMMING

  4. What is an Array? (Example) • Example: 5, 10, 15, 20, and 25. • Previously we would declare five variables: int iNum1, iNum2, iNum3, iNum4, iNum5; • By using array, intaiNum[5]; PGT 106 : C PROGRAMMING

  5. What is an Array? (Example) • 5 components or elements • Elements are referred to index. • Element aiNum[2] has index 2 and value 15. aiNum aiNum[0] aiNum[1] aiNum[2] aiNum[3] aiNum[4] PGT 106 : C 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/subscript PGT 106 : C PROGRAMMING

  7. Arrays in C • 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 • Format: • data_typearray_name[int value]; • const int Max_List_Size = 6; char acAlp[Max_List_Size]; • #define N 10 double adB[N]; • intaiList[5]; • constintMax_Size = 10; intaiHours[Max_Size]; • constint SIZE = 100; double adAmount[SIZE]; PGT 106 : C PROGRAMMING

  9. Multiple Instances vs. Array // multiple instance int iValue1, iValue2, iValue3, iValue4, iValue 5; printf (“Enter first value: “); scanf (“%d”, &iValue1); printf(“Enter second value: “); scanf(“%d”, &iValue2); printf (“Enter third value: “); scanf(“%d”, &iValue3); printf (“Enter fourth value: “); scanf(“%d”, &iValue4) printf (“Enter fifth value: “); scanf(“%d”, &iValue5) PGT 106 : C PROGRAMMING

  10. // array int aiValue[3]; for(int iCount=0; iCount<3; iCount++) { printf (“Enter value : ”); printf (“%d : ”, iCount+1); scanf (“%d”, &aiValue[iCount]); } PGT 106 : C PROGRAMMING

  11. 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 PGT 106 : C PROGRAMMING

  12. 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]; PGT 106 : C PROGRAMMING

  13. 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; PGT 106 : C PROGRAMMING

  14. 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 PGT 106 : C PROGRAMMING

  15. 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. PGT 106 : C PROGRAMMING

  16. 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 PGT 106 : C PROGRAMMING

  17. 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}; PGT 106 : C PROGRAMMING

  18. 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. PGT 106 : C PROGRAMMING

  19. 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); } PGT 106 : C PROGRAMMING

  20. 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. PGT 106 : C PROGRAMMING

  21. 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]); PGT 106 : C PROGRAMMING

  22. Parallel Arrays • Two (or more) arrays are called parallel if their corresponding components hold related information. int aiStudentId[50]; char acStudentGrade[50]; PGT 106 : C PROGRAMMING

  23. 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 PGT 106 : C PROGRAMMING

  24. 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 PGT 106 : C PROGRAMMING

  25. 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 PGT 106 : C PROGRAMMING

  26. 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. PGT 106 : C PROGRAMMING

  27. 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 PGT 106 : C PROGRAMMING

  28. 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) PGT 106 : C PROGRAMMING

  29. 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 PGT 106 : C PROGRAMMING

  30. 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 PGT 106 : C PROGRAMMING

  31. How to overcome? • Use defined loops for (iLoop = 0; iLoop < 10; iLoop ++) aiList [ iLoop ] = 0; PGT 106 : C PROGRAMMING

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

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