古いC++コードをモダンC++に修正(問題編)

問題編

1：動的配列とループ

#include <iostream>

int main() {
    int* arr = new int[5];
    for (int i = 0; i < 5; ++i) {
        arr[i] = i * i;
    }

    for (int i = 0; i < 5; ++i) {
        std::cout << arr[i] << std::endl;
    }

    delete[] arr;
}

2：文字列の配列

#include <iostream>
#include <cstring>

int main() {
    char names[3][10];
    strcpy(names[0], "Alice");
    strcpy(names[1], "Bob");
    strcpy(names[2], "Carol");

    for (int i = 0; i < 3; ++i) {
        std::cout << names[i] << std::endl;
    }
}

3：構造体配列の初期化と出力

#include <iostream>

struct Point {
    int x;
    int y;
};

int main() {
    Point* points = new Point[3];
    points[0].x = 1; points[0].y = 2;
    points[1].x = 3; points[1].y = 4;
    points[2].x = 5; points[2].y = 6;

    for (int i = 0; i < 3; ++i) {
        std::cout << points[i].x << ", " << points[i].y << std::endl;
    }

    delete[] points;
}

4：ポインタの多重管理

#include <iostream>

int main() {
    int* a = new int(10);
    int* b = new int(20);

    int sum = *a + *b;
    std::cout << sum << std::endl;

    delete a;
    delete b;
}

5：整数配列の逆順出力

#include <iostream>

int main() {
    int arr[5] = {10, 20, 30, 40, 50};

    for (int i = 4; i >= 0; --i) {
        std::cout << arr[i] << std::endl;
    }
}

6：文字列の動的配列

#include <iostream>
#include <cstring>

int main() {
    char* names[3];
    names[0] = new char[10];
    names[1] = new char[10];
    names[2] = new char[10];

    strcpy(names[0], "Tom");
    strcpy(names[1], "Bob");
    strcpy(names[2], "Alice");

    for (int i = 0; i < 3; ++i) {
        std::cout << names[i] << std::endl;
    }

    for (int i = 0; i < 3; ++i) delete[] names[i];
}

7：構造体のコピーと参照

#include <iostream>

struct Point {
    int x, y;
};

int main() {
    Point p1 = {1,2};
    Point p2 = p1; // コピー
    p2.x = 10;

    std::cout << p1.x << ", " << p1.y << std::endl;
    std::cout << p2.x << ", " << p2.y << std::endl;
}

8：動的整数2次元配列

#include <iostream>

int main() {
    int rows = 3, cols = 4;
    int** matrix = new int*[rows];
    for (int i = 0; i < rows; ++i) {
        matrix[i] = new int[cols];
        for (int j = 0; j < cols; ++j) {
            matrix[i][j] = i * cols + j;
        }
    }

    for (int i = 0; i < rows; ++i) {
        for (int j = 0; j < cols; ++j) {
            std::cout << matrix[i][j] << " ";
        }
        std::cout << std::endl;
    }

    for (int i = 0; i < rows; ++i) delete[] matrix[i];
    delete[] matrix;
}

9：複合

#include <iostream>
#include <vector>

#define SIZE 5

typedef std::vector<int> IntVector;

int main() {
    int* arr = new int[SIZE];
    for (int i = 0; i < SIZE; ++i) {
        arr[i] = i * 10;
    }

    IntVector* vec = new IntVector();
    for (int i = 0; i < SIZE; ++i) {
        vec->push_back(arr[i]);
    }

    for (int i = 0; i < vec->size(); ++i) {
        std::cout << (*vec)[i] << std::endl;
    }

    delete[] arr;
    delete vec;

    return 0;
}

解答編はこちら↓