Task 1

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#define SIZE 4
#define ROWS 2

void demo1() {
    int arr[SIZE] = {1, 9, 8, 4};
    int i;
    // Output memory size of array arr
    printf("sizeof(arr) = %zu\n", sizeof(arr));
    // Output address and value of each element
    for (i = 0; i < SIZE; ++i)
        printf("%p: %d\n", &arr[i], arr[i]);
    // Output the value of the array name arr
    printf("arr = %p\n", arr);
}

void demo2() {
    int arr[ROWS][SIZE] = {{1, 9, 8, 4}, {2, 0, 4, 9}};
    int i, j;
    // Output memory size of 2D array arr
    printf("sizeof(arr) = %zu\n", sizeof(arr));
    // Output address and value of each element
    for (i = 0; i < ROWS; ++i)
        for (j = 0; j < SIZE; ++j)
            printf("%p: %d\n", &arr[i][j], arr[i][j]);
    printf("\n");
    // Output values of arr, arr[0], arr[1]
    printf("arr = %p\n", arr);
    printf("arr[0] = %p\n", arr[0]);
    printf("arr[1] = %p\n", arr[1]);
    printf("\n");
}

int main() {
    printf("Test 1: 1D array of int\n");
    demo1();
    printf("\nTest 2: 2D array of int\n");
    demo2();
    return 0;
}

Results: ![Screenshot 2025-11-10 225125]

Quession 1: Elements are stored contiguously, each separated by 4 bytes; the array name and the address of the first element are the same.

Question 2: Yes; they are the same; the difference is 16 bytes, representing one row storing 4 integer variables.

Task 2

#include <stdio.h>
#define MAX 100

// Function declarations
void input(int scores[], int count);
double compute(int scores[], int count);

int main() {
    int scores[MAX];
    int count, i;
    double result;
    while (printf("Enter count: "), scanf("%d", &count) != EOF) {
        input(scores, count);
        result = compute(scores, count);
        printf("result = %.2f\n\n", result);
    }
    return 0;
}

// Function definitions
void input(int scores[], int count) {
    for (int i = 0; i < count; ++i)
        scanf("%d", &scores[i]);
}

double compute(int scores[], int count) {
    int i, high, low;
    double sum = 0;
    high = low = scores[0];
    for (i = 0; i < count; ++i) {
        sum += scores[i];
        if (scores[i] > high)
            high = scores[i];
        else if (scores[i] < low)
            low = scores[i];
    }
    return (sum - high - low) / (count - 2);
}

Results: ![Screenshot 2025-11-10 230406]

Question 1: In function input, the formal parameter for the 1D array is int scores[], and the actual parameter is scores.

Question 2: input reads input data and stores it in the array; compute returns the average after dropping the highest and lowest values.

Task 3

#include <stdio.h>
#define MAX 100

// Function declarations
void output(int matrix[][MAX], int size);
void init(int matrix[][MAX], int size, int value);

int main() {
    int matrix[MAX][MAX];
    int size, value;
    while (printf("Enter size and value: "), scanf("%d%d", &size, &value) != EOF) {
        init(matrix, size, value);
        output(matrix, size);
        printf("\n");
    }
    return 0;
}

void output(int matrix[][MAX], int size) {
    for (int i = 0; i < size; ++i) {
        for (int j = 0; j < size; ++j)
            printf("%d ", matrix[i][j]);
        printf("\n");
    }
}

void init(int matrix[][MAX], int size, int value) {
    for (int i = 0; i < size; ++i)
        for (int j = 0; j < size; ++j)
            matrix[i][j] = value;
}

Results: ![Screenshot 2025-11-11 003937]

Question 1: Formal parameter: int matrix[][MAX]; actual parameter: matrix.

Quession 2: No, it will cause an error (the second dimension must be specified).

![Screenshot 2025-11-11 093016]

Task 4

#include <stdio.h>
#define MAX 100

// Function declarations
void input(int numbers[], int count);
double median(int numbers[], int count);

int main() {
    int numbers[MAX];
    int count;
    double result;
    while (printf("Enter count: "), scanf("%d", &count) != EOF) {
        input(numbers, count);
        result = median(numbers, count);
        printf("result = %g\n\n", result);
    }
    return 0;
}

void input(int numbers[], int count) {
    for (int i = 0; i < count; i++) {
        scanf("%d", &numbers[i]);
    }
}

double median(int numbers[], int count) {
    // Bubble sort in descending order
    for (int i = 0; i < count; i++) {
        for (int j = 0; j < count - i - 1; j++) {
            if (numbers[j + 1] > numbers[j]) {
                int tmp = numbers[j];
                numbers[j] = numbers[j + 1];
                numbers[j + 1] = tmp;
            }
        }
    }
    if (count % 2 == 1)
        return numbers[count / 2];
    else
        return (numbers[count / 2] + numbers[count / 2 - 1]) / 2.0;
}

Results: ![Screenshot 2025-11-11 094333]

Task 5

#include <stdio.h>
#define MAX 100

// Function declarations
void input(int matrix[][MAX], int size);
void output(int matrix[][MAX], int size);
void rotate_right(int matrix[][MAX], int size);

int main() {
    int matrix[MAX][MAX];
    int size;
    printf("Enter size: ");
    scanf("%d", &size);
    input(matrix, size);
    printf("Original matrix:\n");
    output(matrix, size);
    rotate_right(matrix, size);
    printf("Matrix after rotation:\n");
    output(matrix, size);
    return 0;
}

void input(int matrix[][MAX], int size) {
    for (int i = 0; i < size; ++i)
        for (int j = 0; j < size; ++j)
            scanf("%d", &matrix[i][j]);
}

void output(int matrix[][MAX], int size) {
    for (int i = 0; i < size; ++i) {
        for (int j = 0; j < size; ++j)
            printf("%4d", matrix[i][j]);
        printf("\n");
    }
}

void rotate_right(int matrix[][MAX], int size) {
    int temp[MAX][MAX];
    for (int i = 0; i < size; i++) {
        for (int j = 0; j < size - 1; j++) {
            temp[i][j + 1] = matrix[i][j];
        }
        temp[i][0] = matrix[i][size - 1];
    }
    for (int i = 0; i < size; i++)
        for (int j = 0; j < size; j++)
            matrix[i][j] = temp[i][j];
}

Results: ![Screenshot 2025-11-11 115646]

Task 6

#include <stdio.h>
#define MAX 100

void dec_to_n(int x, int n);

int main() {
    int x;
    while (printf("Enter a decimal integer: "), scanf("%d", &x) != EOF) {
        dec_to_n(x, 2);
        dec_to_n(x, 8);
        dec_to_n(x, 16);
        printf("\n");
    }
    return 0;
}

void dec_to_n(int x, int n) {
    char digits[] = "0123456789ABCDEF";
    char result[32];
    int index = 0;
    if (x == 0) {
        printf("0\n");
        return;
    }
    while (x > 0) {
        result[index++] = digits[x % n];
        x /= n;
    }
    for (int i = index - 1; i >= 0; i--)
        printf("%c", result[i]);
    printf("\n");
}

Results: ![Screenshot 2025-11-11 161055]

Task 7

#include <stdio.h>
#define MAX 100

void input(int matrix[][MAX], int size);
void output(int matrix[][MAX], int size);
int is_magic(int matrix[][MAX], int size);

int main() {
    int matrix[MAX][MAX];
    int size;
    while (printf("Enter size: "), scanf("%d", &size) != EOF) {
        printf("Enter matrix:\n");
        input(matrix, size);
        printf("Matrix:\n");
        output(matrix, size);
        if (is_magic(matrix, size))
            printf("It is a magic square\n\n");
        else
            printf("It is not a magic square\n\n");
    }
    return 0;
}

void input(int matrix[][MAX], int size) {
    for (int i = 0; i < size; ++i)
        for (int j = 0; j < size; ++j)
            scanf("%d", &matrix[i][j]);
}

void output(int matrix[][MAX], int size) {
    for (int i = 0; i < size; ++i) {
        for (int j = 0; j < size; ++j)
            printf("%4d", matrix[i][j]);
        printf("\n");
    }
}

int is_magic(int matrix[][MAX], int size) {
    int total = size * size;
    int seen[total];
    for (int i = 0; i < total; i++) seen[i] = 0;

    // Check that numbers are 1..total and no duplicates
    for (int i = 0; i < size; i++) {
        for (int j = 0; j < size; j++) {
            int val = matrix[i][j];
            if (val < 1 || val > total) return 0;
            if (seen[val - 1]) return 0;
            seen[val - 1] = 1;
        }
    }

    // Compute reference sum from first row
    int target = 0;
    for (int j = 0; j < size; j++) target += matrix[0][j];

    // Check rows
    for (int i = 0; i < size; i++) {
        int sum = 0;
        for (int j = 0; j < size; j++) sum += matrix[i][j];
        if (sum != target) return 0;
    }

    // Check columns
    for (int j = 0; j < size; j++) {
        int sum = 0;
        for (int i = 0; i < size; i++) sum += matrix[i][j];
        if (sum != target) return 0;
    }

    // Check main diagonal
    int sum_diag1 = 0;
    for (int i = 0; i < size; i++) sum_diag1 += matrix[i][i];
    if (sum_diag1 != target) return 0;

    // Check anti-diagonal
    int sum_diag2 = 0;
    for (int i = 0; i < size; i++) sum_diag2 += matrix[i][size - 1 - i];
    if (sum_diag2 != target) return 0;

    return 1;
}

Results: ![Screenshot 2025-11-11 165416] ![Screenshot 2025-11-11 165654] ![Screenshot 2025-11-11 165709]

Task 8

#include <stdio.h>

int check(int x) {
    int used[10] = {0};
    int square = x * x;
    int cube = x * x * x;
    
    // Extract digits from square
    while (square > 0) {
        int d = square % 10;
        if (used[d]) return 0;
        used[d] = 1;
        square /= 10;
    }
    
    // Extract digits from cube
    while (cube > 0) {
        int d = cube % 10;
        if (used[d]) return 0;
        used[d] = 1;
        cube /= 10;
    }
    
    // Check that all digits 0-9 are used exactly once
    for (int i = 0; i < 10; i++) {
        if (!used[i]) return 0;
    }
    return 1;
}

int main() {
    for (int i = 12; ; i++) {
        if (check(i)) {
            printf("%d\n", i);
            return 0;
        }
    }
}

Results: ![Screenshot 2025-11-11 171702]