Example: Sum of Squares - Formulaic Method in C

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// Sum of Squares - Formulaic Method
#include <stdio.h>

int main() {
    // Step 1: Declare variables for 'n' (input) and 'sum'
    int n;
    long long sum; // Use long long for sum to prevent overflow

    // Step 2: Prompt user for input
    printf("Enter a positive integer (n): ");
    scanf("%d", &n);

    // Step 3: Validate input
    if (n < 1) {
        printf("Please enter a positive integer.\n");
        return 1; // Indicate an error
    }

    // Step 4: Apply the mathematical formula
    // (long long) cast is important here to prevent intermediate multiplication overflow
    // before division, especially for large 'n'.
    sum = (long long)n * (n + 1) * (2 * n + 1) / 6;

    // Step 5: Print the result
    printf("The sum of squares of the first %d natural numbers is: %lld\n", n, sum);

    return 0;
}