Experiment 14 – Dynamic Memory Allocation

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

int main() {
    int *arr_malloc, *arr_calloc, *arr_realloc;
    int n, i, new_size;
    
    printf("Enter number of elements: ");
    scanf("%d", &n);
    
    // Using malloc() - allocates memory, contains garbage values
    arr_malloc = (int*)malloc(n * sizeof(int));
    
    if (arr_malloc == NULL) {
        printf("Memory allocation failed using malloc!\n");
        return 1;
    }
    
    printf("\n--- Using malloc() ---\n");
    printf("Enter %d elements:\n", n);
    for (i = 0; i < n; i++) {
        printf("Element %d: ", i + 1);
        scanf("%d", &arr_malloc[i]);
    }
    
    printf("Array elements (malloc): ");
    for (i = 0; i < n; i++) {
        printf("%d ", arr_malloc[i]);
    }
    printf("\n");
    
    // Using calloc() - allocates memory, initializes to zero
    arr_calloc = (int*)calloc(n, sizeof(int));
    
    if (arr_calloc == NULL) {
        printf("Memory allocation failed using calloc!\n");
        free(arr_malloc);  // Free previously allocated memory
        return 1;
    }
    
    printf("\n--- Using calloc() ---\n");
    printf("Array elements (calloc - initialized to zero): ");
    for (i = 0; i < n; i++) {
        printf("%d ", arr_calloc[i]);
    }
    printf("\n");
    
    printf("Enter %d elements for calloc array:\n", n);
    for (i = 0; i < n; i++) {
        printf("Element %d: ", i + 1);
        scanf("%d", &arr_calloc[i]);
    }
    
    printf("Array elements (calloc after input): ");
    for (i = 0; i < n; i++) {
        printf("%d ", arr_calloc[i]);
    }
    printf("\n");
    
    // Using realloc() - resize previously allocated memory
    printf("\n--- Using realloc() ---\n");
    printf("Enter new size (larger than %d): ", n);
    scanf("%d", &new_size);
    
    arr_realloc = (int*)realloc(arr_malloc, new_size * sizeof(int));
    
    if (arr_realloc == NULL) {
        printf("Memory reallocation failed!\n");
        free(arr_malloc);
        free(arr_calloc);
        return 1;
    }
    
    // If realloc moved the memory, arr_malloc is now invalid
    // Use arr_realloc instead
    printf("Enter %d more elements:\n", new_size - n);
    for (i = n; i < new_size; i++) {
        printf("Element %d: ", i + 1);
        scanf("%d", &arr_realloc[i]);
    }
    
    printf("Array elements after realloc (size %d): ", new_size);
    for (i = 0; i < new_size; i++) {
        printf("%d ", arr_realloc[i]);
    }
    printf("\n");
    
    // Free all allocated memory
    printf("\n--- Freeing Memory ---\n");
    free(arr_realloc);  // Free reallocated memory (or original malloc)
    arr_realloc = NULL;  // Set to NULL to avoid dangling pointer
    
    free(arr_calloc);
    arr_calloc = NULL;
    
    printf("Memory freed successfully!\n");
    
    return 0;
}

// Key Points:
// 1. Always check if malloc/calloc/realloc returns NULL
// 2. Always free dynamically allocated memory
// 3. Set pointer to NULL after freeing
// 4. malloc() - uninitialized memory
// 5. calloc() - zero-initialized memory
// 6. realloc() - can move memory to new location