Introduction to Programming in C

📘 Dynamic Memory Allocation in C (malloc, calloc, free)

In C programming, static memory allocation limits flexibility — memory is assigned at compile time. To create flexible programs that adjust to runtime requirements, we use dynamic memory allocation. This is achieved using malloc, calloc, realloc, and free.

🔹 Why Use Dynamic Memory?

• You don’t always know the required memory size at compile time.
• Efficient memory usage — allocate only what you need.
• Support for dynamic data structures like linked lists, trees, and graphs.

📦 malloc()

malloc stands for memory allocation. It allocates a single block of memory and returns a void pointer.

int *ptr;
ptr = (int *)malloc(5 * sizeof(int)); // allocates memory for 5 integers

📦 calloc()

calloc stands for contiguous allocation. It initializes allocated memory to zero.

int *ptr;
ptr = (int *)calloc(5, sizeof(int)); // allocates and initializes 5 integers to 0

🧠 Difference: malloc() vs calloc()

🔁 realloc()

Reallocate previously allocated memory block to a new size.

ptr = realloc(ptr, 10 * sizeof(int));

🧹 free()

Frees the memory that was dynamically allocated, preventing memory leaks.

free(ptr);

📚 Real-Life Example (UdaanPath)

Imagine UdaanPath allocates space to store student scores entered dynamically at runtime.

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

int main() {
    int *marks;
    int n, i;

    printf("Enter number of students: ");
    scanf("%d", &n);

    marks = (int *)malloc(n * sizeof(int));

    for(i = 0; i < n; i++) {
        printf("Enter marks for student %d: ", i + 1);
        scanf("%d", &marks[i]);
    }

    printf("\nMarks entered on UdaanPath:\n");
    for(i = 0; i < n; i++) {
        printf("Student %d: %d\n", i + 1, marks[i]);
    }

    free(marks); // release memory
    return 0;
}

⚠️ Common Mistakes

• Forgetting to use free()
• Accessing memory after free()
• Using malloc without checking for NULL

📝 Practice Tasks

1. Allocate memory for 10 float values using malloc.
2. Write a program that resizes the memory block with realloc.
3. Create a dynamic array, input values, and print sum.
4. Use calloc to store and display marks for 3 subjects.

✅ Summary

• Dynamic memory is useful for flexible memory usage.
• Use malloc, calloc for allocation, and free for releasing.
• Always check if the pointer is NULL before accessing memory.

🚀 Coming Next

In the next chapter, we will cover Structures and Unions — to combine variables of different types under one name.