C program to dynamically make array and print elements sum

In C programming, dynamic memory allocation allows us to create arrays of variable size at runtime. This is useful when we don't know the array size at compile time. We use malloc() or calloc() functions from the stdlib.h header to allocate memory dynamically.

So, if the input is like n = 6, and array elements 9, 8, 7, 2, 4, 3, then the output will be 33 because sum of 9 + 8 + 7 + 2 + 4 + 3 = 33.

Syntax

int *arr = (int*) malloc(size * sizeof(int));
int *arr = (int*) calloc(size, sizeof(int));

Algorithm

To solve this, we will follow these steps −

• Initialize sum := 0

• Read the size n from input

• Dynamically allocate memory for an array of size n

• Read n elements into the array

• Calculate sum of all array elements

• Display the sum and free allocated memory

Example 1: Using malloc()

Let us see the following implementation using malloc() function −

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

int main() {
    int *arr;
    int n, sum = 0;
    
    printf("Enter number of elements: ");
    scanf("%d", &n);
    
    /* Allocate memory for n integers */
    arr = (int*) malloc(n * sizeof(int));
    
    /* Check if memory allocation was successful */
    if (arr == NULL) {
        printf("Memory allocation failed!<br>");
        return 1;
    }
    
    printf("Enter %d elements: ", n);
    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    /* Calculate sum */
    for (int i = 0; i < n; i++) {
        sum += arr[i];
    }
    
    printf("Sum of array elements: %d<br>", sum);
    
    /* Free allocated memory */
    free(arr);
    return 0;
}

Enter number of elements: 6
Enter 6 elements: 9 8 7 2 4 3
Sum of array elements: 33

Example 2: Using calloc()

Here's the same program using calloc() which initializes allocated memory to zero −

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

int main() {
    int *arr;
    int n, sum = 0;
    
    printf("Enter number of elements: ");
    scanf("%d", &n);
    
    /* Allocate memory for n integers (initialized to 0) */
    arr = (int*) calloc(n, sizeof(int));
    
    if (arr == NULL) {
        printf("Memory allocation failed!<br>");
        return 1;
    }
    
    printf("Enter %d elements: ", n);
    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    for (int i = 0; i < n; i++) {
        sum += arr[i];
    }
    
    printf("Sum of array elements: %d<br>", sum);
    free(arr);
    return 0;
}

Enter number of elements: 4
Enter 4 elements: 5 10 15 20
Sum of array elements: 50

Key Points

• malloc() allocates uninitialized memory, while calloc() initializes memory to zero.
• Always check if memory allocation was successful by comparing with NULL.
• Always call free() to release allocated memory and prevent memory leaks.
• Use sizeof(int) to ensure correct memory size calculation.

Conclusion

Dynamic memory allocation in C using malloc() or calloc() provides flexibility to create arrays of runtime-determined sizes. Remember to always check for allocation success and free the memory after use.