C Exercises: Find the missing number from a given array

#include <stdio.h>

// Function to find the missing number in an array
int pickMissNumber(int *arr1, int ar_size) {
    int i, sum = 0, n = ar_size + 1;

    // Calculating the sum of all elements in the array
    for (i = 0; i < ar_size; i++) {
        sum = sum + arr1[i];
    }

    // Calculating the missing number using the sum of the first 'n' natural numbers formula
    return (n * (n + 1)) / 2 - sum;
}

// Main function
int main() {
    int i;
    int arr1[] = {1, 3, 4, 2, 5, 6, 9, 8};
    int ctr = sizeof(arr1) / sizeof(arr1[0]);

    // Displaying the given array
    printf("The given array is :  ");
    for (i = 0; i < ctr; i++) {
        printf("%d  ", arr1[i]);
    }
    printf("\n");

    // Finding and displaying the missing number
    printf("The missing number is : %d \n", pickMissNumber(arr1, ctr));

    return 0;
}