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CHAPTER 3

CHAPTER 3. ARRAY. Arrays. Introduction to arrays Declaring arrays Initializing arrays Examples using arrays Relationship with pointers Array passing to a function Simple sorting: bubble sort Simple searching: linear sort 2-dimensional array. Array. Introduction Declaration

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CHAPTER 3

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  1. CHAPTER 3 ARRAY Prepared by MMD, Edited by MSY

  2. Arrays • Introduction to arrays • Declaring arrays • Initializing arrays • Examples using arrays • Relationship with pointers • Array passing to a function • Simple sorting: bubble sort • Simple searching: linear sort • 2-dimensional array Prepared by MMD, Edited by MSY

  3. Array Introduction Declaration Initialization Prepared by MMD, Edited by MSY

  4. Introduction to Arrays • Built-in C data types: • Fundamental data types – char, int, double, float, void and variations of int and double. When a variable is declared as one of these types, the compiler reserves a memory location for the variable and it can only store only one value at a time. • Derived data types – derived from fundamental data types eg. pointers, arrays, structures and unions. • An array is a group of memory locations related by the fact that they all have the same name and the same type. Prepared by MMD, Edited by MSY

  5. Introduction to Arrays Cont… • To refer to a particular location or element in the array, we specify the name of the array and the position number of the particular element in the array. • The size of an array is static (fixed) throughout program execution. Prepared by MMD, Edited by MSY

  6. Notice that the position starts from 0. A[0] Name of the array -10 A[1] 99 A[2] -8 A[3] 100 A[4] 27 A[5] 1 A[6] 1976 A[7] Position/index number of the element within the array -2020 A[8] 1 Let say we have an array called A The position number within the square brackets is formally called a subscript. A subscript can be an integer or an integer expression. For example if x = 1 and y = 2, then A [x+y] is A [3]. Prepared by MMD, Edited by MSY

  7. Declaring Arrays • Array declaration is made by specifying the data type and the number of space so that the computer may reserve the appropriate amount of memory. • General syntax: data_type array_name[size] • Examples: • int my_array[100]; • char name[20]; • double bigval[5*200]; • int a[27], b[10], c[76]; Prepared by MMD, Edited by MSY

  8. Initializing Arrays • There are 2 ways to initialize an array: during compilation and during execution. • During compilation: • Unsized array e.g int arr[] = {1, 2, 3, 4, 5}; • We can define how many elements that we want since the array size is not given. • Sized array e.g int arr[3] = {90, 21, 22}; • We can define only 3 elements since the array size is already given. • During execution: int arr[3], j; for (j = 0; j < 3; j++) arr[j] = 0; Prepared by MMD, Edited by MSY

  9. Examples Using Arrays • In the example above, an array with the name temp and size 5 has been declared. The elements in the array has been given the value position*9. The first for loop is equivalent to this: temp[0] = 0*9 temp[3] = 3*9 temp[1] = 1*9 temp[4] = 4*9 temp[2] = 2*9 #include <stdio.h> #define SIZE 5 void main(void) { int temp[SIZE], i; for (i = 0; i < SIZE; i++) temp[i] = i*9; printf(“%s %13s\n”, “Element”, “Value”); for (i = 0; i < SIZE; i++) printf(“%7d%13d\n”, i, temp[i]); } Output: Element Value 0 0 1 9 2 18 3 27 4 36 Prepared by MMD, Edited by MSY

  10. Example: #include <stdio.h> #define SIZE 10 void main(void) { int list[SIZE] = {1, 2, 3, 4, 5, 6, 7, 8, 9}; inti, total = 0; for (i=0; i < SIZE; i++) { total += list[i]; } printf(“Total of array element values is %d.\n”, total); } Output: Total of array element values is 45. Prepared by MMD, Edited by MSY

  11. Example: #include <stdio.h> #define SIZE 20 void main(void) { int list[SIZE]; int n, i, total = 0; float avg; //user enter how many values to key in and validate it printf(“enter the size of the data: ”); scanf(“%d”, &n); if(n<20){ for (i=0; i < n; i++) { //read values and store in array printf(“enter value %d :”, i); scanf(“%d”, &list[i]); total += list[i]; } //find average avg=total/n; printf(“Total of array element values is %d.\n”, total); printf(“Average= %.2f\n”, avg); } else printf(“the size of the data is exceeding the array size”); } Output: Total of array element values is 45. Prepared by MMD, Edited by MSY

  12. Array Relationship with Pointer Array passing to fuction Prepared by MMD, Edited by MSY

  13. Relationship with Pointers • The name of an array is actually a pointer to the first element in the array. • Therefore, if we have: inttest[3] = {9, 10, 11}; printf(“%d”, *test); The output would be: 9 • There are a few ways to traverse an array: int test[3] = {9, 10, 11}, k; for (k = 0; k < 3; k++) printf(“%d\n”, test[k]); int test[3] = {9, 10, 11}, k; int *ptr = test; for (k = 0; k < 3; k++, ptr++) printf(“%d\n”, *ptr); Prepared by MMD, Edited by MSY

  14. Array Passing to a Function • A function that is going to receive an array as one of the arguments can be declared in 2 ways: void Process(char name[])OR void Process(char *name) • When we pass an array to a function, we are actually passing the pointer to the first element in the array to the function. Therefore, any changes to the array inside the function will also change the actual array. • Either the array is passed using [] or using *, the array can be accessed in the same way. Prepared by MMD, Edited by MSY

  15. Passing Array to a Function Cont… • Assume that we have the following array declaration. int marks[10] = {0}; • Say for example we want to write a function, called get_marks, which will read marks from the user and store the marks inside the array. • When we want to pass an array to a function, we need to know these 3 things. • How to write the function prototype? • How to do function call? • How does the function header would look like? Prepared by MMD, Edited by MSY

  16. Passing Array to a Function Cont… • Function prototype: /* data type with square bracket */ void get_marks(int [ ]); void get_marks(int *); /*treating array as pointer */ • Function call: get_marks(marks); /* just pass the array name */ • Function header: void get_marks(int marks[ ]) void get_marks(int *marks) /*treating array as pointers */ Prepared by MMD, Edited by MSY

  17. Example 1: parameter received as an array #include <stdio.h> #define size 10 void get_marks(int [ ]); int calc_average(int [ ]); void main(void) { int marks[size] = {0}; /*initializing the array get_marks(marks); /* function call */ printf(“Average for marks given is %d”, calc_average(marks)); } Prepared by MMD, Edited by MSY

  18. Example 1: parameter received as an array void get_marks(int marks[ ]) { int i; for (i = 0; i < size; i++) { printf("Marks student %d:",i + 1); scanf("%d",&marks[i]); } } int calc_average(int marks[ ]) { int total = 0, i; for (i = 0; i < size; i++) { total = total + marks[i]; } return total / size; } Prepared by MMD, Edited by MSY

  19. Observe the function prototypes Example 2: parameter received as pointers • A function could also receive/treat array parameter as pointer. #include <stdio.h> #define size 10 void get_marks(int *); int calc_average(int *); void main(void) { int marks[size] = {0}; get_marks(marks); printf("Average for marks given is %d\n", calc_average(marks)); } Prepared by MMD, Edited by MSY

  20. Manipulating the memory address Pointer variable Example 2: parameter received as pointers void get_marks(int *marks) { int i; for (i = 0; i < size; i++, marks++) { printf("Marks student %d: ", i + 1); scanf("%d", marks); } } int calculate_average(int *marks) { int i, total = 0; for (i = 0; i < size; i++, marks++) { total = total + *marks; } return (total / size); } Prepared by MMD, Edited by MSY

  21. Example 3: #include <stdio.h> #define SIZE 10 void Read(int []); intCountAvg(int *); void main(void) { int grades[SIZE]; Read(grades); printf(“The average of the grades given is %d\n”, CountAvg(grades)); } void Read(int grades[]) { inti, temp; for (i=0 ; i<SIZE; i++) { printf(“Enter grade %d\n”, i); scanf(“%d”, &temp) grades[i] = temp; } } intCountAvg(int *grades) { inti, total=0; for (i=0; i<SIZE; i++) total += grades[i]; return (total/SIZE); } Prepared by MMD, Edited by MSY

  22. The Read() and CountAvg() functions can also be written this way: void Read(int grades[]) { inti; int *ptr = grades; for (i = 0; i < SIZE; i++, ptr++) { printf(“Enter grade %d\n”, i); scanf(“%d”, &(*ptr)) } } int CountAvg(int *grades) { int i, total; int *ptr = grades; for (i = 0, total = 0; i < SIZE; i++, ptr++) total += *ptr; return (total/SIZE); } Prepared by MMD, Edited by MSY

  23. Array Sorting Searching Prepared by MMD, Edited by MSY

  24. Sorting • Sorting is the process of placing data into a particular order such as ascending or descending. • There are many sorting algorithms that are usually used. Among them are bubble sort, selection sort, insertion sort and shell sort. • Here, we will discuss how bubble sort can be used to sort the elements in an array. Prepared by MMD, Edited by MSY

  25. 1 j k n Sorted Unsorted Bubble Sort • In bubble sort, the list is divided into two sublists: sorted and unsorted. • The smallest element is bubbled from unsorted sublist and moved to the sorted sublist. • Each time an element moves from the unsorted sublist to the sorted sublist, one sort is completed. • The bubble concept is shown in figure below : Prepared by MMD, Edited by MSY

  26. Original list 23 78 45 8 32 56 Unsorted Bubble Sort cont… • Figure below shows how the wall moves one element in each pass. • Looking at the first pass, start with 56 and compare it to 32. Since 56 > 32, it is not moved and we step down one element. • No changes take place until we compare 45 to 8. Since 8 < 45, the two elements are exchanged (swapped). Prepared by MMD, Edited by MSY

  27. 8 23 78 45 32 56 After pass 1 Unsorted Bubble Sort cont… • The two elements are swapped and we step down 1 element. • Because 8 was moved down, it is now compared to 78 and these two elements are swapped. • Finally, 8 is compared to 23 and exchanged. This series of exchanges places 8 in the first location and the wall is moved up one position. Prepared by MMD, Edited by MSY

  28. 8 23 32 78 45 56 After pass 2 Unsorted 8 23 32 45 78 56 After pass 3 Sorted Unsorted 8 23 32 45 56 78 After pass 4 Sorted! Sorted Bubble Sort cont… Prepared by MMD, Edited by MSY

  29. Let us look at the C code: void main(void) { int list[] = {23, 78, 45, 8, 32, 56}; BubbleSort(list); } void BubbleSort (int list[]) { int i, j, temp, swapped = 1; for (i = 0; i < 6 && swapped == 1; i++) { swapped = 0; for (j = 0; j < (6-i); j++) { if (list[j] > list[j+1]) { // Swap temp = list[j]; list[j] = list[j+1]; list[j+1] = temp; swapped = 1; } } } } Prepared by MMD, Edited by MSY

  30. Simple Searching • Searching is the process of determining whether an array contains a value that matches a certain key value. • Same as in sort, there are more than one algorithms that can be used to do a search. • Here, we will discuss how can we do a linear search on an array. • Linear search is a simple searching algorithm where: • data are stored in an array • a key value is compared with each elements in the array starting from the first element Prepared by MMD, Edited by MSY

  31. Let us look at the C code: Sample Output: Enter the number that you want to find: 53 The number 53 is found at location 1 Press any key to continue void main(void) { int list[] = {34, 53, 21, 23, 4}; int i, key_value, found = 0; printf(“Enter the number that you want to find: ”); scanf(“%d”, &key_value); for (i = 0; i < 5; i++) { if (list[i] == key_value) { found = 1; printf(“The number %d is found at location %d\n”, key_value, i); break; } } if (found == 0) printf(“The number %d cannot be found in the list\n”, key_value); } Prepared by MMD, Edited by MSY

  32. Array Multi-Dimensional Array Prepared by MMD, Edited by MSY

  33. 1 2 3 4 5 6 7 8 2-Dimensional Array • It is possible to create an array which has more than one dimension. • For example: • 2D array: int array[4][2]; • 3D array: int array[4][2][10]; • Graphical representation of a 2D array: int myarray[4][2] = {1, 2, 3, 4, 5, 6, 7, 8}; This array has 4 rows and 2 columns. Prepared by MMD, Edited by MSY

  34. 2-Dimensional Array Cont… • Variable initialization can also be done this way: int myarray[4][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}}; int test_score[4][3]={{95,80,78},{69, 75,81}, {100,98,100}, {98,85,87}}; This method is less confusing since we can see the rows and columns division more clearly. • To initialize a 2D array during execution, we need to use a double loop (nested loop): for (i = 0; i < 4; i++) for (j = 0; j < 2; j++) total=total + myarray[i][j]; • Although it is possible to create a multi-dimensional array, arrays above 2-dimensions are rarely used. Prepared by MMD, Edited by MSY

  35. Passing 2D Array to Function • When a 2D (or higher dimensional) array is passed to a function, the size of the second (or subsequent) subscript needs to be specified. • For example, if we have: int twoD[4][5]; Then a function which would taketwoD as an argument should be declared like this:void Process2D(int td[][5]) • An array is stored consecutively in memory regardless of the number of dimensions. Therefore, specifying the subscripts in the function parameter will help the compiler to know the boundary of the different dimensions. Prepared by MMD, Edited by MSY

  36. Example Sample program 1 Sample program 2 Prepared by MMD, Edited by MSY

  37. SUMMARY • In this chapter, we have looked at: • Array declaration and initialization • Reading and writing from/to array elements • Passing array to function • Array sorting : BubbleSort • Simple searching : Linear Search • 2 dimensional array Prepared by MMD, Edited by MSY

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