Arrays

Multi-dimensional initialize & display

Sample programs

Sorting

Searching

Part II

Multidimensional Arrays

a everything about one dimensional arrays applies *

a all elements of the same data type

a just need additional sets of [ ][ ]

a a 3-D array has rows, columns, and rank

* Except leaving the size out of the formal parameter

A

B

C

D

F

28

40

29

9

14

parallel arrays = two or more arrays in which elements with corresponding indexes are related

We WILL do this in the next lab

Parallel Arrays

Used when related data is of different data types.grade % of class

*

Parallel Arrays

for(row…

for(col…{ cout << “Enter id#”;

cin >> id[row][col];

cout << “Enter grade”;cin >> grade[row][col];

}

OR for(row…

for(col…

{ cout << “Enter id and grade”;

cin >> id[row][col] >> grade[row][col];

}

Sum a Row

void main(void){

double nums [3][4] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};

double sumRow(double [3] [4]); // prototype

cout << “The sum of row 3 is “ << sumRow(nums)<<endl; //function call

}

Sum a Row

double sumRow(double ary[3][4]){ int col; double total=0;

for(col = 0; col < 4; col++)total += ary[ ][col];

return total;}

* *

total += ary[2][col]; //enter row # -1

output The sum of row 3 is 42The sum of row 3 is 42

Sum a Column

void main(void){

double nums [3][4] = {1, 2, 33, 4, 5, 6, 77, 8, 9, 10, 1111, 12};

double sumCol(double [3] [4]); // prototype

cout << “The sum of column 3 is “ << sumCol(nums) << endl; //function call

}

Sum a Column

double sumCol(double ary[3][4]){ int row; double total=0;

for(row = 0; row<3; row++)total += ary[row][ ];

return total;}

*

total += ary[row][2]; //enter col # -1

output The sum of column 3 is 21The sum of column 3 is 21

Array Review -1

Write a C++ program that adds equivalent elements of the two-dimensional arrays named first and second. Both arrays should have two rows and three columns. For example, element [1][2] of the resulting array should be the sum of first[1][2] and second[1][2].

first second16 18 23 24 52 7754 91 11 16 19 59

sum40 70 10070 110 70

*

Sorting

Internal Sorts [for small data sets]

bubble (exchange)

selection

External Sorts [for large data sets]

Bubble Sort

Put smaller first

Put smaller first

No change

Put smaller first21 252513 9 1717

2121 252513 9 17

99 252121 13 17

9 2513 21 17

Bubble Sort

Begin again and put smaller first

No change

Put smaller first

21 179 13 25

17 21219 13 2525

2121 171313 9 25

2121 17179 13 25

A Bubble Sort Functionvoid bubble_sort(int array[ ], int length){

int j, k, flag=1, temp;for(j=1; j<=length && flag; j++){

flag=0; // falsefor(k=0; k < (length-j); k++){

if (array[k+1] > array[k]) // > low to high{

temp=array[k+1]; // swaparray[k+1]= array[k];array[k]=temp;flag=1; // indicates a swap

}} }} }} }} // has occurred

Selection Sortindex (k) sm_index

0 2swap 21, 9

1 1swap 13, 13

2 3swap 21, 15

3 4swap 21, 17

21 159 13 17

15 179 13 21

99 152121 13 17

15 21219 13 1717

2121 15159 13 17

Selection Sortvoid sort(double [5]);void swap(double [5], int, int); // prototypesvoid main(void){ int index;

double my_list[ ] = {21, 13, 9, 15, 17};cout << "\nThe unsorted array is: \n";

for(index=0; index<5; index++)cout << “ “ << my_list[index] << endl;

sort(my_list); // function callcout << "\nThe sorted array is: \n";for(index=0; index<5; index++)

cout << “ “ << my_list[index] << endl;}

Selection Sortvoid sort(double testArray[5]){ int n, k, sm_index, pass=0;

double smallest;

for(k=0; k<4; k++) // size-1 = number of passes{ smallest = testArray[k];

sm_index = k;for(n=k+1; n<5; n++) // size = # elem. to look at

if(testArray[n] < smallest){ smallest = testArray[n];

sm_index = n;}

swap(testArray, sm_index, k); // call to swap()}

}

Selection Sort

void swap(double testArray[5], int smaller, int position)

{ // position = current position: kdouble temp;

temp = testArray[position];testArray[position] = testArray[smaller];testArray[smaller] = temp;

}

Linear Search Pseudocode

For all the items in the listCompare the item with the desired itemIf the item was found

Return the index value of the current item(the position of the element in the array)

End IfEnd ForReturn -1 because the item was not found

The “Classic” Linear Search Function

int LinearSearch(int list[], int size, int key){ // or “Sequential search” int i; for (i = 0; i < size; i++) { if (list[i] = = key) return i; // return location of element

//this will terminate the loop } return -1; // element not in list}

Main for linear searchint main() { int LinearSearch(int [], int, int); // prototype const int NUMEL = 10; int nums[NUMEL] = {22,5,67,98,45,32,101,99,73,10}; int item, location; cout << "\nEnter the item you are searching for: "; cin >> item; location = LinearSearch(nums, NUMEL, item); if (location > -1) cout << "The item was found at index location " << location << endl; else cout << "The item was not found in the list\n"; return 0; }

Binary Search

List must be in sorted order

The function looks at the midpoint

If the midpoint is the item, return the location

Else, determine if the item is less than or greater than the midpoint

Eliminate the side where the item cannot be, and declare a new midpoint

Go again. (A recursive function)

Half the list is eliminated on each pass

int BinarySearch(int list[], int size, int key) { int left, right, midpt; // list must be in sorted order left = 0; // left end is the first element right = size - 1; // right is the last element while (left <= right){ midpt = (int) ((left + right) / 2); // why integer division? if (key == list[midpt]) return midpt; // if found, the key will be the midpoint else if (key > list[midpt]) // eliminate the left half left = midpt + 1; else right = midpt - 1; // else - eliminate the right half } // end whilereturn -1;} // the key was never found

Main for binary searchint main() { int BinarySearch(int [], int, int); // prototype const int NUMEL = 10; int nums[NUMEL] = {5,10,22,32,45,67,73,98,99,101}; int item, location; cout << "\nEnter the item you are searching for: "; cin >> item; location = BinarySearch(nums, NUMEL, item); if (location > -1) cout << "The item was found at index location " << location << endl; else cout << "The item was not found in the list\n"; return 0; }

Array Review

a is an ordered sequence of dataof the same type

a can be of any valid data type

a can be 1-, 2-, or multi- dimensional

a must be declared before used

a can be assigned and initialized

a element numbering starts at zero

Array Review

a use for loops to access (nested for multidimentional)

a can be passed back and forth between functions

a when sent to functions the actual values are manipulated - not a copy

(passed by reference)

Array Review - 6a

There is an array of three students each with four exam scores. Assume the scores are known and are: {77, 68, 86, 73}, {96, 87, 89, 78}, {70, 90, 86, 81}. Create a program which will display the lowest grade, the highest grade and the average of the grades to two decimal places.

Array Review - 6b

#include <iostream>#include <iomanip.>using namespace std;

const int STUDENTS = 3; // global, so main and allconst int EXAMS = 4; // functions can access

int mini (int [][EXAMS], int, int);

int maxi (int [][EXAMS], int, int);

float average(int [], int);

void printArray(int [][EXAMS], int, int);

Array Review - 6cvoid main(void){ int studentGrades[STUDENTS][EXAMS] =

{{77, 68, 86, 73}, {96, 87, 89, 78}, {70, 90, 86, 81}};

cout << "The array is:" << endl; printArray(studentGrades, STUDENTS, EXAMS); cout<<endl<<endl<<"Lowest grade: " << mini (studentGrades, STUDENTS, EXAMS)

<< endl << "Highest grade: " << maxi (studentGrades, STUDENTS, EXAMS)<<endl;

for (int person = 0; person < STUDENTS; person++) cout << "The average grade for student " << person << " is " <<setiosflags(ios::fixed | ios::showpoint)<<setprecision(2) << average(studentGrades[person], EXAMS) << endl;}

Array Review - 6d

int mini(int grades[][EXAMS], int pupils, int tests)

{ int lowGrade = 100; for (int i = 0; i < pupils; i++) for (int j = 0; j < tests; j++) if (grades[i][j] < lowGrade) lowGrade = grades[i][j]; return lowGrade; }

int maxi(int grades[][EXAMS], int pupils, int tests)

{ int highGrade = 0; for (int i = 0; i < pupils; i++) for (int j = 0; j < tests; j++) if (grades[i][j] > highGrade) highGrade = grades[i][j]; return highGrade; }

Array Review - 6e

float average(int setOfGrades[],int tests)

{ int total = 0; for (int i = 0; i < tests; i++) total += setOfGrades[i]; return (float) total / tests; }

void printArray(int grades[][EXAMS], int pupils, int tests) { cout << " [0] [1] [2] [3]"; for (int i = 0; i < pupils; i++) { cout << endl<< "studentGrades["

<< i << "] ";

for (int j = 0; j < tests; j++) cout << setiosflags(ios::left)

<< setw(5) << grades[i][j]; }

Array Review - 6f

function call:average(studentGrades[person],

EXAMS)

float average(int setOfGrades[], int tests){ int total = 0;

for (int i = 0; i < tests; i++) total += setOfGrades[i];

return total / tests;}

Common Errors

Not declaring the arrayNot declaring the array First element is called First element is called zerozero; last element ; last element

is one less than the number of elementsis one less than the number of elements Out of rangeOut of range subscripts - no warning subscripts - no warning Error in the Error in the forfor loop - check the counter loop - check the counter Not initializing the arrayNot initializing the array

Common Errors

Aggregate operations not allowedAggregate operations not allowed Omitting array size - permitted only Omitting array size - permitted only

when declared as a formal parameter when declared as a formal parameter initialized in the declarationinitialized in the declaration

If array is /* in */ only, declare the If array is /* in */ only, declare the formal parameter as formal parameter as constconst to prevent to prevent accidental modificationaccidental modification

Debugging

array subscriptsarray subscripts

recheck array size in declaration, recheck array size in declaration, initialization, and initialization, and forfor loops loops

Prevention - plan first!Prevention - plan first!Valuation tablesValuation tablesDisplay values with coutDisplay values with cout

C++ DebuggerC++ Debugger

I really hate this darn machine,I really hate this darn machine,

I wish they would sell it.I wish they would sell it.

It never does quite what I want,It never does quite what I want,

But only what I tell it.But only what I tell it.

End Note