Heap and Stack Memory

Exercise 17 – Heap and Stack Memory in C

Hi! Today I worked on Exercise 17: Heap and Stack Memory Allocation, and it was definitely one of the toughest ones so far . This exercise makes a small database program that can store names and emails, but the real focus is on memory allocation – stack vs heap.

What This Program Does

• Creates a tiny address book database using struct.

• Lets us create, set, get, delete, and list records in the database.

• Introduces file I/O in C (fopen, fread, fwrite, fclose).

• Shows how heap memory (malloc) and stack memory are different.

Example Code 

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

#define MAX_DATA 512
#define MAX_ROWS 100

struct Address {
    int id;
    int set;
    char name[MAX_DATA];
    char email[MAX_DATA];
};

struct Database {
    struct Address rows[MAX_ROWS];
};

int main() {
    struct Database *db = malloc(sizeof(struct Database)); // Heap memory
    if (!db) {
        printf("Memory allocation failed!\n");
        return 1;
    }

    // Example entry
    db->rows[0].id = 0;
    db->rows[0].set = 1;
    strncpy(db->rows[0].name, "Rahul", MAX_DATA);
    strncpy(db->rows[0].email, "rahul@example.com", MAX_DATA);

    printf("ID: %d, Name: %s, Email: %s\n",
           db->rows[0].id, db->rows[0].name, db->rows[0].email);

    free(db); // Release heap memory
    return 0;
}

Heap vs Stack – Easy Way to Remember

Stack

• Stores local variables (inside functions).

• Works like a stack of plates → last in, first out (LIFO).

• Memory is fast but limited.

• Freed automatically when function ends.

• Too much use = stack overflow.

Heap

• Stores dynamic memory (you request it using malloc / new).

• Works like a storage warehouse → you must manage space yourself.

• Memory is larger but slower.

• You must free it manually (free / delete).

• Forgetting to free = memory leak.

Shortcut to remember:

• Stack = Automatic (fast, small)

• Heap = Manual (big, slow)

Example Output

$ ./ex17 db.dat c
$ ./ex17 db.dat s 1 Rahul rahul@gmail.com
$ ./ex17 db.dat s 2 Daksh daksh@yahoo.com
$ ./ex17 db.dat l
1 Rahul rahul@gmail.com
2 Daksh daksh@yahoo.com

How did I learned it as?

This exercise taught me that:

• Heap is for big, flexible memory .

• Stack is for temporary, automatic memory (local variables).

• Always free your malloc or your program will eat memory forever.

• Using structs and arrays together makes database-like programs possible even in C.