C: المؤشرات المتقدمة

int x = 42;
int *p = &x;
int **pp = &p;

**pp = 100;
printf("%d\n", x);

100

void alloc_buf(char **ptr, int size) {
    *ptr = (char *)malloc(size);
}

int main(void) {
    char *buf = NULL;
    alloc_buf(&buf, 128);
    if (buf) {
        strcpy(buf, "hello");
        printf("%s\n", buf);
        free(buf);
    }
    return 0;
}

hello

int a = 10, b = 20, c = 30;
int *arr[3] = {&a, &b, &c};
for (int i = 0; i < 3; i++) {
    printf("%d ", *arr[i]);
}

10 20 30

const char *names[3] = {"Alice", "Bob", "Carol"};
for (int i = 0; i < 3; i++) {
    printf("%s\n", names[i]);
}

Alice
Bob
Carol

int matrix[3][4] = {
    {1, 2, 3, 4},
    {5, 6, 7, 8},
    {9, 10, 11, 12}
};
int (*p)[4] = matrix;
printf("%d\n", p[1][2]);

7

#include <stdio.h>

void print_matrix(int (*m)[4], int rows) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < 4; j++) {
            printf("%3d", m[i][j]);
        }
        printf("\n");
    }
}

int main(void) {
    int matrix[2][4] = {
        {10, 20, 30, 40},
        {50, 60, 70, 80}
    };
    print_matrix(matrix, 2);

    const char *fruits[3] = {"apple", "banana", "cherry"};
    for (int i = 0; i < 3; i++) {
        printf("%s ", fruits[i]);
    }
    printf("\n");
    return 0;
}

 10 20 30 40
 50 60 70 80
apple banana cherry

int (*pf)(int, int);

int add(int a, int b) { return a + b; }
int sub(int a, int b) { return a - b; }

int main(void) {
    int (*pf)(int, int) = add;
    printf("%d\n", pf(3, 5));
    pf = sub;
    printf("%d\n", pf(10, 4));
    return 0;
}

8
6

void process(int *arr, int len, int (*transform)(int)) {
    for (int i = 0; i < len; i++) {
        arr[i] = transform(arr[i]);
    }
}

int double_it(int n) { return n * 2; }
int negate(int n) { return -n; }

int main(void) {
    int data[4] = {1, 2, 3, 4};
    process(data, 4, double_it);
    for (int i = 0; i < 4; i++) printf("%d ", data[i]);

    printf("\n");
    process(data, 4, negate);
    for (int i = 0; i < 4; i++) printf("%d ", data[i]);
    return 0;
}

2 4 6 8
-2 -4 -6 -8

#include <stdio.h>
#include <stdlib.h>

int cmp_asc(const void *a, const void *b) {
    return *(int *)a - *(int *)b;
}

int cmp_desc(const void *a, const void *b) {
    return *(int *)b - *(int *)a;
}

void sort_and_print(int *arr, int n, int (*cmp)(const void *, const void *)) {
    qsort(arr, n, sizeof(int), cmp);
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main(void) {
    int nums[5] = {42, 7, 19, 3, 55};
    sort_and_print(nums, 5, cmp_asc);

    int nums2[5] = {42, 7, 19, 3, 55};
    sort_and_print(nums2, 5, cmp_desc);
    return 0;
}

3 7 19 42 55
55 42 19 7 3

const int *p;
int const *p;

int a = 10, b = 20;
const int *p = &a;
printf("%d\n", *p);
p = &b;
printf("%d\n", *p);

10
20

int * const p = &a;

int a = 10;
int * const p = &a;
*p = 99;
printf("%d\n", a);

99

const int * const p = &a;

int a = 42;
double b = 3.14;
void *p;

p = &a;
printf("%d\n", *(int *)p);

p = &b;
printf("%.2f\n", *(double *)p);

42
3.14