Lecture 21

Reading

p419-421, 422-430

Additional notes on new

Consider the following example 
double *array;
int size = 10;
array = new double[size];
The new operator does 2 things When you should use dynamic arrays?
One more simple example 
#include<iostream>
using namespace std;

int main() {
    int size;
    int *squares;


    cout << "Enter an integer: ";
    cin >> size;

    squares = new int[size];

    for(int i = 0; i < size; i++) {
        squares[i] = i*i;
    }

    return 0;
}
What is the output of square[3] if size is 10?





One more example on returning an array 
#include<iostream>
using namespace std;

// return an array with the first element is 1, the seconde element is 2 ....
int* integers(int size);

int main() {
    int size = 20;
    int* result;

    result = integers(size);

    for(int i = 0; i < 20; i++) {
        cout << result[i] << " ";
    }
    cout << endl;

    return 0;
}

int* integers(int size) {
    int *temp = new int[size]; // create a pointer to an array
    for(int i = 0; i < size; i++) {
        temp[i] = i+1; // assign value
    }

    return temp; // return the pointer(array)
}

Use pointer in functions


Example 
#include<iostream>
using namespace std;

void increaseByOne(int* array, int size);
void display(int* array, int size);

int main() {
    int a[] = {2,4,6,8};
    int size = 4;
    display(a,4);
    cout << endl;
    increaseByOne(a, 4);
    display(a,4);
    cout << endl;
    return 0;
}


void increaseByOne(int* array, int size) {
    for(int i = 0; i < size; i++) {
        array[i]++;
    }
}

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







Some people like to write it in this way 
#include<iostream>
using namespace std;

typedef int* IntPtr;

void increaseByOne(IntPtr array, int size);
void display(IntPtr array, int size);

int main() {
    int a[] = {2,4,6,8};
    int size = 4;
    display(a,4);
    cout << endl;
    increaseByOne(a, 4);
    display(a,4);
    cout << endl;
    return 0;
}

void increaseByOne(IntPtr array, int size) {
    for(int i = 0; i < size; i++) {
        array[i]++;
    }
}

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

What is the output of the following program? 
#include<iostream>
using namespace std;


void f1(double* a);
void f2(double* a, double* b);
void f3(double* a, double*& b);


int main() {
    double *a, *b, x=10, y=20;
    a = &x;
    b = &y;
    cout << x << endl;
    cout << *a << endl;
    cout << y << endl;
    cout << *b << endl;
    cout << endl;
    f1(a);
    cout << x << endl;
    cout << *a << endl;
    cout << y << endl;
    cout << *b << endl;
    cout << endl;
    f2(a,b);
    cout << x << endl;
    cout << *a << endl;
    cout << y << endl;
    cout << *b << endl;
    cout << endl; 
    f3(a,b);
    cout << x << endl;
    cout << *a << endl;
    cout << y << endl;
    cout << *b << endl;
     

    return 0;

}

void f1(double* a) {
    *a = 7;
}

void f2(double* a, double* b) {
    *a = 55;
    b = a;
}

void f3(double* a, double*& b) {
    *a = 55;
    b = a;
}
One more example 
#include<iostream>
#include<cctype>
using namespace std;

// change the string to uppercase letters
char* changeToUpper(char* s);

int main() {
    char string[] = "abcdefghijklmnopqrstuvwxyz1234567890";
    char* upper;
    upper = changeToUpper(string);
    cout << string << endl
         << upper << endl;

    return 0;
}


char* changeToUpper(char* s) {
    int length = strlen(s); // the length of the string
    char* result = new char[length+1]; // dynamically created an array

    for(int i = 0; i < length; i++) {
        result[i] = toupper(s[i]); // return the uppercase letter of s[i]
    }
    result[length] = '\0'; // don't forget the null character
    return result;
}

Output 
abcdefghijklmnopqrstuvwxyz1234567890
ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890