1. CS 1400 10 Nov 2006 Example using dynamic arrays

2. Problem: Find the mode of an array The mode of a list of numbers is defined as the number that occurs most frequently in the list Initial pseudocode; allocate a new array big enough for the list read the list of numbers into the array find and output the mode of the array deallocate the array

3. First refinement… int size, *array; cout << “Enter size of the list: “; cin >> size; array = new int[size]; read the list of numbers into the array find and output the mode of the array delete[] array;

4. Second refinement… int main() {int size, *array; cout << “Enter size of the list: “; cin >> size; array = new int[size]; FillArray(array, size); cout << “Mode is: “ << FindMode(array, size); delete[] array; }

5. read the list of numbers into the array void FillArray (int *p, int size) {cout << “Enter “ << size << “ values: “; for (int n=0; n<size; n++) cin >> p[n]; }

6. find and output the mode of the array int FindMode (int *p, int size) {allocate a same-sized array to hold value counts for each value in p; count the number of times this value occurs in p and save in counts array find the position of the maximum in counts array deallocate the counts array return the value in p at this position }

7. First refinement… int FindMode (int *p, int size) {int *counts, value, position; counts = new int[size]; for each value in p; count the number of times this value occurs in p and save in counts array find the position of the maximum in counts array delete[] counts; return p[position]; }

8. Second refinement… int FindMode (int *p, int size) {int *counts, value, position; counts = new int[size]; for (int n=0; n<size; n++) {count the number of times this value occurs in p and save in counts array } find the position of the maximum in counts array delete[] counts; return p[position]; }

9. Third refinement… int FindMode (int *p, int size) {int *counts, value, position; counts = new int[size]; for (int n=0; n<size; n++) {value = p[n]; counts[n] = CountValue(p, size, value); } find the position of the maximum in counts array delete[] counts; return p[position]; }

10. Fourth refinement… int FindMode (int *p, int size) {int *counts, value, position; counts = new int[size]; for (int n=0; n<size; n++) {value = p[n]; counts[n] = CountValue(p, size, value); } position = FindPosOfMax(counts, size); delete[] counts; return p[position]; }

11. count number of times value occurs in p int CountValue (int *q, int size, int value) {int count = 0; for each value in array q; if this cell of array q equals value count++; return count; }

12. First refinement… int CountValue (int *q, int size, int value) {int count = 0; for (int n=0; n<size; n++) if (q[n] == value) count++; return count; }

13. find the position of the maximum in w int FindPosOfMax (int *w, int size) {int position = 0, max = w[0]; for each remaining cell in array w (past index 0) if this cell is greater than max; set max to this cell set position to this index return position; }

14. First refinement… int FindPosOfMax (int *w, int size) {int position = 0, max = w[0]; for (int n=1; n<size; n++) if (w[n] > max) {set max to this cell set position to this index } return position; }

15. Second refinement… int FindPosOfMax (int *w, int size) {int position = 0, max = w[0]; for (int n=1; n<size; n++) if (w[n] > max) {max = w[n]; position = n; } return position; }