PIC10A Lecture 14

Partially-filled Arrays

Example 
//Shows the difference between each of a list of golf scores and their average.
#include <iostream>
using namespace std;
const int MAX_NUMBER_SCORES = 10;
 
void fillArray(int a[], int size, int& numberUsed);
//Precondition: size is the declared size of the array a.
//Postcondition: numberUsed is the number of values stored in a.
//a[0] through a[numberUsed-1] have been filled with
//nonnegative integers read from the keyboard.

double computeAverage(const int a[], int numberUsed);
//Precondition: a[0] through a[numberUsed-1] have values; numberUsed > 0.
//Returns the average of numbers a[0] through a[numberUsed-1].

void showDifference(const int a[], int numberUsed);
//Precondition: The first numberUsed indexed variables of a have values.
//Postcondition: Gives screen output showing how much each of the first 
//numberUsed elements of the array a differ from their average.

int main( )
{
    int score[MAX_NUMBER_SCORES], numberUsed;

    cout << "This program reads golf scores and shows\n"
         << "how much each differs from the average.\n";

    cout << "Enter golf scores:\n";
    fillArray(score, MAX_NUMBER_SCORES, numberUsed);
    showDifference(score, numberUsed);

    return 0;
}

void fillArray(int a[], int size, int& numberUsed)
{
    cout << "Enter up to " << size << " nonnegative whole numbers.\n"
         << "Mark the end of the list with a negative number.\n";

    int next, index = 0;
    cin >> next;
    while ((next >= 0) && (index < size))
    {
        a[index] = next;
        index++;
        cin >> next;
    }

    numberUsed = index;
}

double computeAverage(const int a[], int numberUsed)
{
    double total = 0;
    for (int index = 0; index < numberUsed; index++)
        total = total + a[index];
    if (numberUsed > 0)
    {
        return (total/numberUsed);
    }
    else
    {
        cout << "ERROR: number of elements is 0 in computeAverage.\n"
             << "computeAverage returns 0.\n";
        return 0;
    }
}

void showDifference(const int a[], int numberUsed)
{
    double average = computeAverage(a, numberUsed);
    cout << "Average of the " << numberUsed 
         << " scores = " << average << endl
         << "The scores are:\n";
    for (int index = 0; index < numberUsed; index++)
    cout << a[index] << " differs from average by "
         << (a[index] - average) << endl;
}
Output
This program reads golf scores and shows
how much each differs from the average.
Enter golf scores:
Enter up to 10 nonnegative whole numbers.
Mark the end of the list with a negative number.
70 73 69 68 -1
Average of the 4 scores = 70
The scores are:
70 differs from average by 0
73 differs from average by 3
69 differs from average by -1
68 differs from average by -2

Multidimensional arrays

Example

There are 3 pic10a lectures. Each lecture has at most 100 students. Write a 2 dimensional array to represent all the scores.
Answer 
double score[3][100];
It can be visualize as
Lecture 1 score[0][0], score[0][1], ......, score[0][99]
Lecture 2 score[1][0], score[1][1], ......, score[1][99]
Lecture 3 score[2][0], score[2][1], ......, score[2][99]

Example 
#include<iostream>
using namespace std;

int main() {
    const int STUDENT_NUM = 4;
    double score[STUDENT_NUM][3] = 
    {{32.5, 67, 93.2},
    {99.25, 98.2, 99},
    {50.7, 60.3, 70.2},
    {80.2, 70.8, 65}};

    cout.setf(ios::fixed);
    cout.setf(ios::showpoint);
    cout.precision(2);
    
    int i;
    cout << "Homework    Midterm     Exam        Final Score\n";
    for(i = 0; i < STUDENT_NUM; i++) {
        cout << score[i][0] << "       " 
             << score[i][1] << "       "
             << score[i][2] << "       "
             << 0.3*score[i][0] + 0.25*score[i][1] + 0.45*score[i][2]
             << endl;
    }

    return 0;
}
Output
Homework    Midterm     Exam        Final Score
32.50       67.00       93.20       68.44
99.25       98.20       99.00       98.88
50.70       60.30       70.20       61.88
80.20       70.80       65.00       71.01
Another way to write the program is 
#include<iostream>
using namespace std;

// find the final score
double final(double score[]); 

int main() {
    const int STUDENT_NUM = 4;
    double score[STUDENT_NUM][3] = 
    {{32.5, 67, 93.2},
    {99.25, 98.2, 99},
    {50.7, 60.3, 70.2},
    {80.2, 70.8, 65}};

    cout.setf(ios::fixed);
    cout.setf(ios::showpoint);
    cout.precision(2);
    
    int i;
    cout << "Homework    Midterm     Exam        Final Score\n";
    for(i = 0; i < STUDENT_NUM; i++) {
        cout << score[i][0] << "       " 
             << score[i][1] << "       "
             << score[i][2] << "       "
             << final(score[i])
             << endl;
    }

    return 0;
}


double final(double score[]) {
    return 0.3*score[0] + 0.25*score[1] + 0.45*score[2];
}
Explanation Multidimensional Array Parameters
We won't discuss it. Please refer to the book.