Transcript Arrays
Arrays
Multi-dimensional initialize & display Sample programs Sorting Searching Part II
Multidimensional Arrays
a a a a everything about one dimensional arrays applies * all elements of the same data type just need additional sets of
[ ]
a 3-D array has rows, columns, and rank * Except leaving the size out of the formal parameter
Parallel Arrays
Used when related data is of different data types.
grade % of class
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
for(row… OR for(col… { cout << “Enter id#”; cin >> id[row][col]; cout << “Enter grade”; cin >> grade[row][col]; } 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)< double { sumRow(double ary[3][4]) int col; double total=0; for(col = 0; col < 4; col++) //enter row # -1 } return total; output The sum of row 3 is 42 * * void main(void) { double nums [3][4] = {1, 2, 3 , 4, 5, 6, 7 , 8, 9, 10, 11 , 12}; double sumCol(double [3] [4]); // prototype } cout << “The sum of column 3 is “ << sumCol(nums) << endl; //function call double sumCol(double ary[3][4]) { int row; double total=0; for(row = 0; row<3; row++) total += ary[row][ ]; //enter col # -1 return total; } output The sum of column 3 is 21 * 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]. 16 54 first 18 91 23 11 40 sum 70 70 110 100 70 24 16 second 52 19 77 59 * Internal Sorts [for small data sets] bubble (exchange) selection External Sorts [for large data sets] 21 13 9 25 17 Put smaller first 13 21 9 25 17 Put smaller first 13 9 21 25 17 No change 13 9 21 25 17 Put smaller first 13 9 21 17 25 9 13 21 17 25 Begin again and put smaller first No change 9 13 21 17 25 Put smaller first 9 13 17 21 25 void bubble_sort(int array[ ], int length) { int j, k, flag=1, temp; for(j=1; j<=length && flag; j++) { flag=0; // false for(k=0; k < (length-j); k++) { if (array[k+1] > array[k]) // > { temp=array[k+1]; low to high // swap } } } } array[k+1]= array[k]; array[k]=temp; flag=1; // indicates a swap // has occurred 21 13 9 15 17 index (k) sm_index 0 2 swap 21, 9 9 13 21 15 17 1 1 swap 13, 13 9 13 21 15 17 2 3 swap 21, 15 9 13 15 21 17 3 4 swap 21, 17 9 13 15 17 21 void sort(double [5]); void swap(double [5], int, int); void main(void) // prototypes { 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); cout << "\nThe sorted array is: \n"; // function call for(index=0; index<5; index++) cout << “ “ << my_list[index] << endl; } void sort(double testArray[5]) { int n, k, sm_index, pass=0; double smallest; } for(k=0; k<4; k++) { smallest = testArray[k]; sm_index = k; for(n=k+1; n<5; n++) { // size-1 = number of passes // size = # elem. to look at if(testArray[n] < smallest) smallest = testArray[n]; sm_index = n; } swap(testArray, sm_index, k); // call to swap() } void swap(double testArray[5], int smaller, int position) { // position = current position: k double temp; } temp = testArray[position]; testArray[position] = testArray[smaller]; testArray[smaller] = temp; For all the items in the list Compare the item with the desired item If the item was found Return the index value of the current item (the position of the element in the array) End If End For Return -1 because the item was not found 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 int 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; } 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 left, right, midpt; left = 0; right = size - 1; // list must be in sorted order // left end is the first element // 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]) left = midpt + 1; // eliminate the left half else right = midpt - 1; // else - eliminate the right half } // end while return -1;} // the key was never found int 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; } a a a a a a is an ordered sequence of data of the same type can be of any valid data type can be 1-, 2-, or multi- dimensional must be declared before used can be assigned and initialized element numbering starts at zero a a a use for loops to access (nested for multidimentional) can be passed back and forth between functions when sent to functions the actual values are manipulated - not a copy (passed by reference) 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. #include void 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< 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; } float average(int setOfGrades[], void printArray(int grades[][EXAMS], int tests) int pupils, int tests) { { int total = 0; cout << " [0] [1] [2] [3]"; for (int i = 0; i < tests; i++) for (int i = 0; i < pupils; i++) { total += setOfGrades[i]; return (float) total / tests; cout << endl<< "studentGrades[" << i << "] "; } for (int j = 0; j < tests; j++) cout << setiosflags(ios::left) << setw(5) << grades[i][j]; } 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; } Not declaring the array First element is called zero ; last element is one less than the number of elements Out of range subscripts - no warning Error in the for loop - check the counter Not initializing the array Aggregate operations not allowed Omitting array size - permitted only when declared as a formal parameter initialized in the declaration If array is /* in */ only, declare the formal parameter as const to prevent accidental modification array subscripts recheck array size in declaration, initialization, and for loops Prevention - plan first! Valuation tables Display values with cout C++ DebuggerSum a Row
Sum a Column
Sum a Column
Array Review -1
Sorting
Bubble Sort
Bubble Sort
A Bubble Sort Function
Selection Sort
Selection Sort
Selection Sort
Selection Sort
Linear Search Pseudocode
The “Classic” Linear Search Function
Main for linear search
Binary Search
int BinarySearch(int list[], int size, int key)
Main for binary search
Array Review
Array Review
Array Review - 6a
Array Review - 6b
Array Review - 6c
Array Review - 6d
Array Review - 6e
Array Review - 6f
Common Errors
Common Errors
Debugging
End Note
I really hate this darn machine, I wish they would sell it.
It never does quite what I want, But only what I tell it.