1. Dynamic Memory Allocation and Pointer Vairable Example

Input and run the program, observe the output, and explain the purpose of each line.

#include<iostream>
using namespace std;
int main(){
    int *ptr, index;
    ptr = new int[5];
    if (ptr == NULL)
        exit(0);
    *(ptr + 1) = 3;
    for (index = 0; index < 5; index++)
        cout << *(ptr + index) << " ";
    delete[] ptr;
    return 0;
}

1.1 Program Analysis

int *ptr, index; // Declare an integer pointer and an integer variable
ptr = new int[5]; // Allocate memory for five integers dynamically
if (ptr == NULL) // Check if memory allocation was successful
    exit(0); // Exit if allocation failed
*(ptr + 1) = 3; // Assign value 3 to the second element of the array
for (index = 0; index < 5; index++) // Loop through all elements in the array
    cout << *(ptr + index) << " "; // Output each element with a space separator
delete[] ptr; // Free the dynamically allocated memory
return 0; // End the program

1.2 Output

-842150451 3 -842150451 -842150451 -842150451

2. Reference Definition and Usage Example

Input and run the program, observe the output, and explain the purpose of each line.

#include<iostream>
using namespace std;
int main(){
    int num = 10;
    int &ref = num;
    cout << "num=" << num << endl;
    cout << "ref=" << ref << endl;
    cout << "&num=" << &num << endl;
    cout << "&ref=" << &ref << endl;
    return 0;
}

2.1 Program Analysis

int num = 10; // Define an integer variable and assign it a value of 10
int &ref = num; // Define ref as a reference to num
cout << "num=" << num << endl; // Output the value of num
cout << "ref=" << ref << endl; // Output the value of ref
cout << "&num=" << &num << endl; // Output the address of num
cout << "&ref=" << &ref << endl; // Output the address of ref
return 0; // End the program

2.2 Output

num=10
ref=10
&num=00B3FE9C
&ref=00B3FE9C

3. Pointer to Structure Variable Example

Input and run the program, observe the output, and explain the purpose of each line.

#include<iostream>
using namespace std;
struct student{
    long int id;
    char name[4];
    float grade;
};
int main(){
    student data = {89031, "LiL", 96};
    student *ptr = &data;
    cout << data.id << " " << data.name << " " << data.grade << endl;
    cout << ptr->id << " " << ptr->name << " " << ptr->grade << endl;
    cout << (*ptr).id << " " << (*ptr).name << " " << (*ptr).grade << endl;
    return 0;
}

3.1 Program Analysis

struct student{ // Define a student structure
    long int id; // Define a long integer variable for ID
    char name[4]; // Define a character array for name
    float grade; // Define a float variable for grade
};
int main(){
    student data = {89031, "LiL", 96}; // Define and initialize a structure variable
    student *ptr = &data; // Define a pointer to the structure
    cout << data.id << " " << data.name << " " << data.grade << endl; // Access structure members
    cout << ptr->id << " " << ptr->name << " " << ptr->grade << endl; // Use arrow operator to access members
    cout << (*ptr).id << " " << (*ptr).name << " " << (*ptr).grade << endl; // Use dereference operator to access members
    return 0;

3.2 Output

89031 LiL 96
89031 LiL 96
89031 LiL 96

4. Program Design

Define a dynamic integer array (length provided by user), loop to assign values to array elements. Use pointers to swap the smallest value with the first element and the largest value with the last element. Output the modified array.

4.1 Source Code

#include<iostream>
using namespace std;
int main(){
    int size;
    cout << "Array length: ";
    cin >> size;
    int *array = new int[size];
    cout << "Enter " << size << " numbers";
    for (int i = 0; i < size; i++) {
        cin >> array[i];
    }
    int *minVal = array;
    int *maxVal = array;
    for (int *p = array + 1; p < array + size; p++) {
        if (*p < *minVal) {
            minVal = p;
        }
        if (*p > *maxVal) {
            maxVal = p;
        }
    }
    if (minVal != array) {
        int temp = *array;
        *array = *minVal;
        *minVal = temp;
    }
    if (maxVal != array + size - 1) {
        int temp = *(array + size - 1);
        *(array + size - 1) = *maxVal;
        *maxVal = temp;
    }
    cout << "Output: ";
    for (int *p = array; p < array + size; p++) {
        cout << *p << " ";
    }
    cout << endl;
    delete[] array;
    return 0;
}

4.2 Program Analysis

First, define a variable for the array size, then input the speicfic length. Dynamically allocate memory for the array. Then read the specified number of elements into the array. Define pointers for the minimum and maximum values, traverse the array to find the corresponding elements. If the minimum is not at the first position, swap it with the first element. If the maximum is not at the last position, swap it with the last element. After swapping, use a pointer to print out all the elements. Finally, free the dynamically allocated memory and return from the function.