Difference between Static and Dynamic Memory Allocation in C

In C++, memory allocation is a process by which computer programs and services are assigned physical or virtual memory space. The memory allocation is done either before or at the time of program execution.

There are two types of memory allocations: 

1. Compile-time or Static Memory Allocation
2. Run-time or Dynamic Memory Allocation

Static and dynamic memory allocation in C have different use cases and implications:

Let's take a look at each of them.

Static Memory Allocation

Static Memory is allocated for declared variables by the compiler. The address can be found using the address of operator and can be assigned to a pointer. The memory is allocated during compile time.

Example:

#include <stdio.h>

int main() {
    
    // Static memory allocation 
    // of an array
    int arr[5] = {1, 2, 3, 4, 5};

    // Printing the array elements
    for (int i = 0; i < 5; i++) {
        printf("arr[%d] = %d\n", i, arr[i]);
    }
    
    return 0;
}

arr[0] = 1
arr[1] = 2
arr[2] = 3
arr[3] = 4
arr[4] = 5

In the above program, the array arr of size 5 is statically allocated, and it holds 5 integers. The memory for this array is fixed and is allocated when the program starts, based on the declared size.

Dynamic Memory Allocation

Memory allocation done at the time of execution(run time) is known as dynamic memory allocation. Functions calloc() and malloc() support allocating dynamic memory. In the Dynamic allocation of memory space is allocated by using these functions when the value is returned by functions and assigned to pointer variables.

Example:

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

int main() {
    
    // Dynamically allocate memory 
    // for an array of 5 integers
    int *arr = (int*)malloc(5 * sizeof(int));

    // Initialize the array with values
    for (int i = 0; i < 5; i++) {
        arr[i] = i + 1;
    }

    // Print the array elements
    for (int i = 0; i < 5; i++) {
        printf("arr[%d] = %d\n", i, arr[i]);
    }

    return 0;
}

arr[0] = 1
arr[1] = 2
arr[2] = 3
arr[3] = 4
arr[4] = 5

This program dynamically allocates memory for an array of 5 integers using malloc, initializes the array with values 1 to 5, and prints the elements. It demonstrates basic dynamic memory allocation in C.