array prepared by mmd, edited by msy1. introduction to arrays declaring arrays initializing...
TRANSCRIPT
CHAPTER 3ARRAY
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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
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Arrays
ArrayIntroductionDeclaration
Initialization
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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.
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Introduction to Arrays
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.
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Introduction to Arrays Cont…
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Let say we have an array called A
Name of the array
The position number withinthe square brackets is formallycalled a subscript. A subscriptcan be an integer or an integerexpression. For example if x = 1 and y = 2, then A [x+y]is A [3].
Notice that the positionstarts from 0.
Position/index number of theelement within the array
-10
99
-8
100
27
1976
-2020
1
A[0]
A[1]
A[2]
A[3]
A[4]
A[5]
A[6]
A[7]
A[8]
1
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];
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Declaring Arrays
There are 2 ways to initialize an array: during compilation and during execution.
1. 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.
2. During execution:int arr[3], j;for (j = 0; j < 3; j++) arr[j] = 0;
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Initializing 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*9temp[1] = 1*9 temp[4] = 4*9temp[2] = 2*9
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Examples Using Arrays
#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 Value0 01 92 183 274 36
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Example:#include <stdio.h>#define SIZE 10
void main(void) { int list[SIZE] = {1, 2, 3, 4, 5, 6, 7, 8, 9}; int i, 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.
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#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 itprintf(“enter the size of the data: ”);scanf(“%d”, &n);
if(n<20){ for (i=0; i < n; i++) {
//read values and store in arrayprintf(“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”); }
Example:
Output: Total of array element values is 45.
ArrayRelationship with PointerArray passing to fuction
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The name of an array is actually a pointer to the first element in the array.
Therefore, if we have:int test[3] = {9, 10, 11};
printf(“%d”, *test); The output would be: 9 There are a few ways to traverse an array:
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Relationship with Pointers
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);
A function that is going to receive an array as one of the arguments can be declared in 2 ways:void Process(char name[]) ORvoid 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.
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Array Passing to a Function
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?
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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 */
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Passing Array to a Function Cont…
#include <stdio.h>#define size 10void get_marks(int [ ]);int calc_average(int [ ]);
void main(void){int marks[size] = {0}; /*initializing the arrayget_marks(marks); /* function call */printf(“Average for marks given is %d”, calc_average(marks));
}
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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]);}
}
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Example 1: parameter received as an array
int calc_average(int marks[ ]){
int total = 0, i;for (i = 0; i < size; i++){
total = total + marks[i];}return total / size;
}
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));
}
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Example 2: parameter received as pointers
Observe the function prototypes
void get_marks(int *marks){int i;for (i = 0; i < size; i++, marks++){
printf("Marks student %d: ", i + 1);
scanf("%d", marks);}
}
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Example 2: parameter received as pointers
int calculate_average(int *marks){
int i, total = 0;for (i = 0; i < size; i++, marks++){
total = total + *marks;}
return (total / size);}
Manipulating the memory address
Pointer variable
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Example 3:
#include <stdio.h>#define SIZE 10
void Read(int []);int CountAvg(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[]) { int i, temp; for (i=0 ; i<SIZE; i++) { printf(“Enter grade %d\n”, i); scanf(“%d”, &temp) grades[i] = temp; }}
int CountAvg(int *grades) { int i, total=0; for (i=0; i<SIZE; i++) total += grades[i]; return (total/SIZE);}
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The Read() and CountAvg() functions can also be written this way:
void Read(int grades[]) { int i; 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);}
ArraySorting
Searching
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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.
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Sorting
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 :
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Bubble Sort
1 j nk
Sorted Unsorted
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).
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Bubble Sort cont…
23 78 845 32 56
Unsorted
Original list
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.
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Bubble Sort cont…
23 788 45 32 56
Unsorted
After pass 1
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Bubble Sort cont…
23 328 78 45 56
Unsorted
After pass 2
23 328 45 78 56
Unsorted
After pass 3
Sorted
23 788 4532 56 After pass 4Sorted!
Sorted
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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; } } }}
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
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Simple Searching
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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);}
Let us look at the C code:
Sample Output:Enter the number that you want to find:
53The number 53 is found at location 1Press any key to continue
ArrayMulti-Dimensional Array
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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:
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2-Dimensional Array
int myarray[4][2] = {1, 2, 3, 4, 5, 6, 7, 8};
1 2
3 4
5 6
7 8
This array has 4 rows and 2 columns.
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.
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2-Dimensional Array Cont…
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 take twoD 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.
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Passing 2D Array to Function
Sample program 1Sample program 2
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Example
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
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SUMMARY