C++: المؤشرات والمصفوفات

#include <iostream>

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 
 std::cout << "arr = " << arr << std::endl;
 std::cout << "&arr[0] = " << &arr[0] << std::endl;
 // Both output the same! Because arr is &arr[0]
 
 return 0;
}

arr = 0x7ffd4a3b
&arr[0] = 0x7ffd4a3b

#include <iostream>

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 int* p = arr; // p points to first element
 
 // Method 1: Subscript（same as array）
 std::cout << "arr[0] = " << p[0] << std::endl; // 10
 std::cout << "arr[1] = " << p[1] << std::endl; // 20
 
 // Method 2: Dereference
 std::cout << "*p = " << *p << std::endl; // 10
 std::cout << "*(p+1) = " << *(p+1) << std::endl; // 20
 
 return 0;
}

#include <iostream>

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 int* p = arr; // Pointing to arr[0]
 
 std::cout << "p = " << p << std::endl; // Assume 0x1000
 std::cout << "p + 1 = " << p + 1 << std::endl; // 0x1004（Not 0x1001!）
 std::cout << "p + 2 = " << p + 2 << std::endl; // 0x1008
 
 return 0;
}

#include <iostream>

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 int* p1 = &arr[0]; // Pointing to arr[0]
 int* p2 = &arr[3]; // Pointing to arr[3]
 
 std::cout << "p2 - p1 = " << p2 - p1 << std::endl; // 3（Number of elements）
 
 return 0;
}

#include <iostream>

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 
 // Method 1: Subscript（Most common）
 std::cout << "Method 1: Subscript" << std::endl;
 for (int i = 0; i < 5; i++) {
 std::cout << arr[i] << " ";
 }
 std::cout << std::endl;
 
 // Method 2: Pointer arithmetic
 std::cout << "Method 2: Pointer arithmetic" << std::endl;
 for (int* p = arr; p < arr + 5; p++) {
 std::cout << *p << " ";
 }
 std::cout << std::endl;
 
 // Method 3: Use standard library function (will learn later)
 // std::cout << "Method 3: std::begin/end" << std::endl;
 // for (int* p = std::begin(arr); p != std::end(arr); p++) {
 // std::cout << *p << " ";
 // }
 
 return 0;
}

Method 1: Subscript
10 20 30 40 50 
Method 2: Pointer arithmetic
10 20 30 40 50 

#include <iostream>

void printSize(int arr) {
 // arr is actually a pointer, not an array!
 std::cout << "sizeof(arr) = " << sizeof(arr) << std::endl; // 8（64-bit system, pointer size）
}

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 
 std::cout << "sizeof(arr) = " << sizeof(arr) << std::endl; // 20（5 x 4 = 20 bytes）
 printSize(arr);
 
 return 0;
}

#include <iostream>

// Must additionally pass array size
void printArray(int arr, int size) {
 for (int i = 0; i < size; i++) {
 std::cout << arr[i] << " ";
 }
 std::cout << std::endl;
}

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 printArray(arr, 5); // Pass array name (which is first element address)
 return 0;
}

#include <iostream>

void reverseArray(int* arr, int size) {
 int* left = arr; // Pointing to first element
 int* right = arr + size - 1; // Pointing to last element
 
 while (left < right) {
 // Swap values pointed to by left and right
 int temp = *left;
 *left = *right;
 *right = temp;
 
 left++; // Move right
 right--; // Move left
 }
}

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 
 std::cout << "Before reversal: ";
 for (int i = 0; i < 5; i++) {
 std::cout << arr[i] << " ";
 }
 std::cout << std::endl;
 
 reverseArray(arr, 5);
 
 std::cout << "After reversal: ";
 for (int i = 0; i < 5; i++) {
 std::cout << arr[i] << " ";
 }
 std::cout << std::endl;
 
 return 0;
}

Before reversal: 10 20 30 40 50 
After reversal: 50 40 30 20 10 

#include <iostream>

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 int* p = arr;
 
 std::cout << *(p + 10) << std::endl; // ❌ Out of bounds! p+10 points outside array
 // Outputs garbage value, or program crashes
 
 return 0;
}

#include <iostream>

int main() {
 int x = 5;
 int y = 10;
 int* p1 = &x;
 int* p2 = &y;
 
 std::cout << p2 - p1 << std::endl; // ❌ Undefined behavior! p1 and p2 point to different arrays
 // Only subtracting pointers to the same array is meaningful
 
 return 0;
}

#include <iostream>

int main() {
    int arr[] = {10, 20, 30, 40, 50};
    int* p = arr;

    for (int i = 0; i < 5; i++) {
        std::cout << "*(p+" << i << ")=" << *(p + i) << std::endl;
    }

    return 0;
}

*(p+0)=10
*(p+1)=20
*(p+2)=30
*(p+3)=40
*(p+4)=50