PIC10A Lecture 18

Reading

p224-236, p191-203

Structure

Use array and other structure in a sturcutre

You can use arrays as members of a structure.
You can also use other structures as members of a structure.

#include<iostream>
using namespace std;

struct Date {
    int month;
    int day;
    int year;
};


struct Employee {
    char name[51]; // 50 characters
    char gender;
    Date birthday;// Date, defined above
    double income;
};



// display information of employee
void display(Employee employee); 

// display information of date, function overloading
void display(Date date);

int main() {
    // magic formula
    cout.setf(ios::fixed);
    cout.setf(ios::showpoint);
    cout.precision(2);
    // --------------- name,  gender,  date ,  income
    Employee david = {"David", 'M', {11,1,71}, 122322.22};
    display(david);
    cout << endl;

    Employee mary;
    // setting mary's data
    strcpy(mary.name,"Mary");
    mary.gender = 'F';
    Date date = {5,6,80};
    mary.birthday = date;
    mary.income = 31415;
    
    display(mary);

    return 0;
    
}

void display(Employee employee) {
    cout << "Name: " << employee.name << endl
         << "Gender: " << employee.gender << endl
         << "Date of Birth: ";
    display(employee.birthday);
    cout << endl
         << "Annual income: " << employee.income << endl;
         
}

void display(Date date) {
    cout << date.month << "/" << date.day << "/" << date.year;
}

Output

Name: David
Gender: M
Date of Birth: 11/1/71
Annual income: 122322.22

Name: Mary
Gender: F
Date of Birth: 5/6/80
Annual income: 31415.00

Another example

#include<iostream>
using namespace std;

struct Score {
    char classID[10];
    int studentNum; // less than a 100;
    double scores[100];
};

double average(Score score);

int main() {
     // magic formula
    cout.setf(ios::fixed);
    cout.setf(ios::showpoint);
    cout.precision(2);
    //------------ classID, studentNum, scores
    Score score = {"PIC10A", 5, {85.2, 30.1, 42, 55.55, 98}};
    cout << "The average score of " 
         << score.classID << " class is " 
         << average(score) << endl;

    return 0;
}

double average(Score score) {
    double sum=0;
    for(int i=0; i < score.studentNum; i++) {
        sum+=score.scores[i];
    }
    return sum/score.studentNum;
}

Output

The average score of PIC10A class is 62.17

Use structure in array

You can use structure in an array

Example

#include<iostream>
using namespace std;

struct Date {
    int month;
    int day;
    int year;
};

void display(Date date);

int main() {
    Date holidays[3] = {{12,25,2002}, {11,11,2002}, {1,1, 2003}};
    for(int i = 0; i < 3; i++) {
        display(holidays[i]);
        cout << endl;
    }
    
    return 0;
}

void display(Date date) {
    cout << date.month << "/" << date.day << "/" << date.year;
}

Output

12/25/2002
11/11/2002
1/1/2003

Sorting

Program

#include<iostream>
using namespace std;

// return the index of the minimun after startIndex
int minIndex(int a[], int size, int startIndex);

// swap the content of 2 integers. 
void swap(int& a, int& b);

// sort the array use selection sort
void sort(int a[], int size);

// display the array
void display(int a[], int size);

int main() {
    int a[] = {8,6,10,2,16,4,18,14,12,20};
    cout << "Before sorting: \n";
    display(a,10);
    cout << endl;
    sort(a, 10);
    cout << "After sorting: \n";
    display(a,10);
    cout << endl;

    return 0;
}

int minIndex(int a[], int size, int startIndex) {
    int min = a[startIndex]; // assume the first one is the min
    int minInd = startIndex;
    for(int i = startIndex + 1; i < size; i++) {
        if(min > a[i]) { // a[i] is actually smaller
            minInd = i;
            min = a[i]; 
        }
    }
    return minInd;
}

void swap(int& a, int& b) {
    int temp = a;
    a = b;
    b = temp;
}

void sort(int a[], int size) {
    for(int i = 0; i < size; i++) {
        int minInd = minIndex(a, size, i);
        // swap a[i] and a[minInd]
        swap(a[i], a[minInd]);
    }
}

void display(int a[], int size) {
    for(int i = 0; i < size; i++) {
        cout << a[i] << " ";
    }
}

Output

Before sorting:
8 6 10 2 16 4 18 14 12 20
After sorting:
2 4 6 8 10 12 14 16 18 20

The smallest number is 2(index is 3)

a[0]	a[1]	a[2]	a[3]	a[4]	a[5]	a[6]	a[7]	a[9]	a[9]
8	6	10	2	16	4	18	14	12	20

Exchange it with the 0th element.

a[0]	a[1]	a[2]	a[3]	a[4]	a[5]	a[6]	a[7]	a[9]	a[9]
2	6	10	8	16	4	18	14	12	20

The next smallest number is 4 (index is 5)

a[0]	a[1]	a[2]	a[3]	a[4]	a[5]	a[6]	a[7]	a[9]	a[9]
2	6	10	8	16	4	18	14	12	20

Exchange it with the element right after 2.

a[0]	a[1]	a[2]	a[3]	a[4]	a[5]	a[6]	a[7]	a[9]	a[9]
2	4	10	8	16	6	18	14	12	20

The next smallest number is 6 (index is 5)

a[0]	a[1]	a[2]	a[3]	a[4]	a[5]	a[6]	a[7]	a[9]	a[9]
2	4	10	8	16	6	18	14	12	20

Exchange it with the element right after 4.

a[0]	a[1]	a[2]	a[3]	a[4]	a[5]	a[6]	a[7]	a[9]	a[9]
2	4	6	8	16	10	18	14	12	20

The process goes on till all the numbers are sorted.

for(int index = 0; index < size; index++)  {
   place the indexth smallest element in a[index];
}

In more details

for(int index = 0; index < size; index++) {
    find the smallest element among a[index], a[index+1],...,a[size-1]
	let the index corresponding the the element be minIndex
	swap a[index] and a[minIndex]
}

How to find the min element and the min index?
Assume the first one is the smallest. min is 3, minIndex is 0.

Compare the min 3, to the 1st element 2. 2 is smaller.
Now min is 2, minIndex is 1.

Compare 2 to the next element 5. 2 is still the min.

Compare 2, to the next element 1. 1 is smaller.
Now min is 1, minIndex is 3.

Compare 1 to the next element 4. 1 remains the smallest.
min is 1, minIndex is 3

The codes

int min = a[0];
int minIndex = 0;
for(int index = 1; index < size; i++) {
   compare min to a[index]
   if a[index] is smaller
       minIndex = index
       min = a[index]
}

Swap
The following swap function won't work. Why?

void swap(int& a, int& b) {
   a = b;
   b = a;
}

The correct one is

void swap(int& a, int& b) {
    int temp = a;
    a = b;
    b = temp;
}