Data Structure: Storing and Organizing Data Efficiently

1. Data Structure(s) • A way of storing and organizing data in a computer so that it can be used efficiently. • e.g. • Arrays • Linked Lists • stacks • Queues • Trees etc

2. Arrays

3. Array • Consecutive group of memory locations • Same name • Same type (int, char, etc.)

4. Declaring Arrays • When declaring arrays, specify • Type of array • Name • Number of elements • type arrayName[arraySize]; int c[ 10 ]; // array of 10 integers float d[ 3284 ]; // array of 3284 floats • Declaring multiple arrays of same type • Use comma separated list, like regular variables int b[ 100 ], x[ 27 ];

5. Initializing Arrays • Initializing arrays • For loop • Set each element • Initializer list • Specify each element when array declared int n[ 5 ] = { 1, 2, 3, 4, 5 }; • If not enough initializers, rightmost elements 0 • If too many syntax error

6. To set every element to 0 int n[ 5 ] = { 0 }; • If array size omitted, Initializer determine size int n[] = { 1, 2, 3, 4, 5 }; • 5 Initializer, therefore 5 element array

7. Array elements like other variables • Assignment, printing for an integer array c c[ 0 ] = 3; cout << c[ 0 ]; • A subscript must be an integer or integer expression. • Can perform operations inside subscript c[ 5 – 2 ] same as c[3]

8. To refer to an element • Specify array name and position number (index/subscript) • Format: arrayname[ position number ] • First element at position 0 • N-element array c c[ 0 ], c[ 1 ] … c[ n - 1 ] • Nth element as position N-1

9. Example #include <iostream> using namespace std; void main() { int n[ 5]={4,5, 6,10,12}; cout<<"Array elements\n"; cout<<n[0]<<endl; cout<<n[1]<<endl; cout<<n[2]<<endl; cout<<n[3]<<endl; cout<<n[4]<<endl; }

10. Example #include <iostream> using namespace std; void main() { int n[ 10 ]={4,5, 6,10,12}; cout<<"Array elements\n"; for ( int i = 0; i < 5; i++ ) cout<<n[i]<<endl; }

11. Find the sum and average of one dimensional integer array.

12. Allow the user to input integers in an array only if the integer is even.

13. Find the smallest element of an array

14. Passing Arrays to Functions

15. Passing Arrays to Functions • Specify name without brackets • To pass array myArray to myFunction int myArray[ 24 ]; myFunction( myArray, 24 ); • Array size usually passed, but not required • Useful to iterate over all elements

16. Passing Arrays to Functions • Arrays passed-by-reference • Functions can modify original array data • Value of name of array is address of first element • Function knows where the array is stored • Can change original memory locations • Individual array elements passed-by-value • Like regular variables • square( myArray[3] );

17. Passing Arrays to Functions • Functions taking arrays • Function prototype • void modifyArray( int b[], int arraySize ); • void modifyArray( int [], int ); • Names optional in prototype • Both take an integer array and a single integer • No need for array size between brackets • Ignored by compiler • If declare array parameter as const • Cannot be modified (compiler error) • void doNotModify( const int [] );

18. Example (Passing Array to Functions) void function1(int [], int); void function2(int); void main () { const int size=5; int array[]={1, 2,3 ,4,5}; cout<<"Array elements before function call:"; for (int i=0; i<5;i++) cout<<array[i]<<" "; cout<<endl;

19. function1(array, 5); cout<<endl; cout<<"Array elements after function call\n"; for (i=0; i<size;i++) cout<<array[i]<<" "; cout<<endl; cout<<endl; cout<<"passing array element array[2] to the function\n"; cout<<"Before:"<<array[2]<<endl; function2(array[2]); cout<<"After:"<<array[2]<<endl; }

20. //function definitions void function1(int a[],int size) { cout<<"Array elements in function call\n"; for (int i=0; i<size; i++) cout<<(a[i]*=2)<<" "; } void function2( int x) { cout<<"In Function:"; cout<<x*2<<endl; }

21. Searching Arrays

22. Searching Arrays: Linear Search • Search array for a key value • Linear search • Compare each element of array with key value • Start at one end, go to other • Useful for small and unsorted arrays • Inefficient • If search key not present, examines every element

23. Example (Array Search) #include<iostream> using namespace std; void main () { const int size=10; int a[size]={ 5,6,1,8,3,7,2,10,9,4}; for(int k=0; k<size; k++) cout<<a[k]<<" "; cout<<endl; int searchKey; cout << "Enter integer search key: "; cin >> searchKey;

24. for( k=0; k<size; k++) if (a[k]==searchKey) cout<<"The element to be searched is found at index a["<<k<<"]"; cout<<endl; }

25. Array Sorting

26. Sorting Arrays • Sorting data • Important computing application • Virtually every organization must sort some data • Bubble sort • Several passes through the array (assume: elements are to be sorted in increasing order) • Successive pairs of elements are compared • If increasing order (or identical), no change • If decreasing order, elements exchanged • Repeat these steps for every element

27. Sorting Arrays • Example: • Go left to right, and exchange elements as necessary • One pass for each element Original: 3 4 2 7 6 Pass 1: 3 2 46 7 (elements exchanged) Pass 2: 2 3 4 6 7 Pass 3: 2 3 4 6 7 (no changes needed) Pass 4: 2 3 4 6 7 Pass 5: 2 3 4 6 7

28. Sorting Arrays • Swapping variables int x = 3, y = 4; y = x; x = y; • What happened? • Both x and y are 3! • Need a temporary variable • Solution int x = 3, y = 4, temp = 0; temp = x; // temp gets 3 x = y; // x gets 4 y = temp; // y gets 3

29. Example (Array Sorting) #include<iostream> using namespace std; void main () { const int size=10; int a[size]={ 5,6,1,8,3,7,2,10,9,4}; for(int k=0; k<size; k++) cout<<a[k]<<" "; cout<<endl;

30. int temp; //sorting process for ( int pass = 0; pass < size - 1; pass++ ) for ( int j = 0; j < size - 1; j++ ) // loop to control number of comparisons per pass if ( a[ j ] > a[ j + 1 ] ) { temp = a[ j ]; a[ j ] = a[ j + 1 ]; a[ j + 1 ] = temp; } cout<<"Sorted Array\n"; for( k=0; k<size; k++) cout<<a[k]<<" "; cout<<endl; }

31. Character Arrays

32. Character Arrays • 2 kinds of strings • C-Strings • Objects of String class

33. Contd… • Strings • Arrays of characters • All strings end with null ('\0') • Examples • char string1[] = "hello"; • Null character implicitly added • string1 has 6 elements • char string1[] = { 'h', 'e', 'l', 'l', 'o', '\0’ }; • Subscripting is the same String1[ 0 ] is 'h' string1[ 2 ] is 'l'

34. Contd… • Input from keyboard char string2[ 10 ]; cin >> string2; • Puts user input in string • Stops at first whitespace character • Adds null character • If too much text entered, data written beyond array • Printing strings • cout << string2 << endl; • Does not work for other array types • Characters printed until null found

35. Example (C-String Variable) #include<iostream> using namespace std; int main () { char a[20]; cout<<"Enter String\n"; cin>>a; cout<<"you entered "<<a<<endl; return 0; }

36. Example (String Constants) #include<iostream> using namespace std; int main () { char question[] = "Please, enter your first name: "; char greeting[] = "Hello, "; char yourname [80]; cout << question; cin >> yourname; cout << greeting << yourname << "!"<<endl; return 0; }

37. Example (Reading Embedded Blanks) #include<iostream> using namespace std; int main () { char question[] = "Please, enter your first name: "; char greeting[] = "Hello, "; char yourname [80]; cout << question; cin.get(yourname,80); cout << greeting << yourname << "!"<<endl; return 0; }

38. Copying string #include <iostream> using namespace std; int main() { char a1[50]="This is a string"; char a2[50]; for (int i=0;a1[i]!='\0'; i++) a2[i]=a1[i]; a2[i]='\0'; cout<<a2<<endl; return 0; }

39. Easy way! #include <iostream> using namespace std; int main() { char a1[50]="This is a string"; char a2[50]; strcpy(a2,a1); cout<<a2<<endl; return 0; }

40. strlen, strcpy() & strcmp() • Strlen (array); tells the length of the array • Strcpy(destination, source); Copies the source values to the destination • Strcmp(str1, str2); compares two strings str1 & str2 and gives the integer value. • 0 indicates the matching strings • Otherwise not same

41. String class • No need to specify array size (responsibility of memory management) • Input and output similar to C-Strings

42. Example #include<iostream> #include<string> using namespace std; int main () { string question = "Please, enter your first name: "; string greeting ("Hello, "); string yourname; cout << question; getline(cin, yourname); cout<<greeting+yourname<<endl; return 0; }

43. 2 Dimensional Arrays

44. Column 0 Column 1 Column 2 Column 3 a[ 0 ][ 3 ] a[ 1 ][ 0 ] a[ 2 ][ 3 ] a[ 2 ][ 2 ] a[ 1 ][ 3 ] a[ 0 ][ 0 ] a[ 1 ][ 1 ] a[ 2 ][ 1 ] a[ 0 ][ 2 ] a[ 1 ][ 2 ] a[ 2 ][ 0 ] a[ 0 ][ 1 ] Row 0 Row 1 Row 2 Multiple-Subscripted Arrays • Multiple subscripts • a[ i ][ j ] • Tables with rows and columns • Specify row, then column • “Array of arrays” • a[0] is an array of 4 elements • a[0][0] is the first element of that array Column subscript Array name Row subscript

45. 1 2 3 4 1 0 3 4 Multiple-Subscripted Arrays • To initialize • Initializersgrouped by row in braces int b[ 2 ][ 2 ] = { { 1, 2 }, { 3, 4 } }; int b[ 2 ][ 2 ] = { { 1 }, { 3, 4 } }; Row 0 Row 1

46. 1 0 3 4 Multiple-Subscripted Arrays • Referenced like normal cout << b[ 0 ][ 1 ]; • Outputs 0 • Cannot reference using commas cout << b[ 0, 1 ]; • Syntax error • Function prototypes • Must specify sizes of subscripts • First subscript not necessary, as with single-scripted arrays • void printArray( int [][ 3 ] );

47. Example //print the total of 2D array elements #include<iostream.h> int main () { int a[3][3]={1,2,3,4,5,6,7,8,9}; cout<<"Array a is:\n"; for (inti=0; i<3;i++) { for (int j=0;j<3;j++) cout<<a[i][j]<<" "; cout<<endl; }

48. int total=0; for (inti=0; i<3;i++) for (int j=0;j<3;j++) total+= a[i][j]; cout<<“Total of Array elements is:”<<total<<endl return 0; }

49. Example (Passing 2D Arrays to Functions) #include<iostream.h> void add(int a[3][3], int b[3][3]) { for (inti=0; i<3;i++) { for (int j=0;j<3;j++) cout<<(a[i][j]+b[i][j])<<" "; cout<<endl; } }

50. int main() { int a[][3]={1,2,3,4,5,6,7,8,9}; int b[][3]={1,2,3,4,5,6,7,8,9}; cout<<"Array a is:\n"; for (inti=0; i<3;i++) { for (int j=0;j<3;j++) cout<<a[i][j]<<" "; cout<<endl; }