/*
 * Author  : Amit Dutta <amitdutta4255@gmail.com>
 * Date    : 12 Dec 2025
 * Repo    : https://github.com/notamitgamer/bsc
 * License : MIT License (See the LICENSE file for details)
 */

/* Write a function that receives integers and returns the sum, average
and standard deviation of these numbers. Call this function from main()
and print the result in main() */
/* Let Us C, Chap - 9, Page 158, Problem 9.1 */

#include <stdio.h>
#include <math.h>

// Function prototype: Using pointers for 'call by reference' to return 3 values.
void stats(double *, double *, double *);

int main()
{
    double sum, average, standardDeviation;
    // Passing addresses of variables to receive results from the function.
    stats(&sum, &average, &standardDeviation);

    printf("\n--- Stats ---"
           "\nSum: %g"
           "\nAverage: %g"
           "\nStandard Deviation: %g",
           sum, average, standardDeviation);
    return 0;
}

// Function to calculate statistics on user-provided numbers.
void stats(double *sum, double *average, double *standardDeviation)
{
    int n;
    // Input Validation Loop for N
    do
    {
        printf("How many numbers you want to give input: ");

        if (scanf("%d", &n) == 1)
        {
            break;
        }
        else
        {
            printf("\nPlease enter a valid number.\n");
            // Clearing input buffer to handle invalid input
            while (getchar() != '\n' && !feof(stdin))
                ;
        }
    } while (1);

    // Variable-Length Array (VLA) to store the input numbers.
    double inputNumber[n];
    int i = 0;

    printf("\n--- Enter Numbers ---\n");

    // Input Loop for numbers
    while (i < n)
    {
        printf("Enter number %d: ", i + 1);

        if (scanf("%lf", &inputNumber[i]) == 1)
        {
            // Clearing input buffer after successful read
            while (getchar() != '\n')
                ;
            i++;
        }
        else
        {
            printf("Invalid input. Only integers are allowed. Please try again.\n");
            // Clearing input buffer to handle invalid input
            while (getchar() != '\n' && !feof(stdin))
                ;
        }
    }

    // 1. Sum Calculation
    double tempSum = 0;
    for (i = 0; i < n; i++)
        tempSum += inputNumber[i];

    // 2. Average (Mean) calculation
    double tempAverage = tempSum / n;

    // 3. Standard Deviation (Sample SD formula used)
    double tempStandardDeviation = 0.0;

    // Preventing division by zero if n is 1. SD is 0 for a single number.
    if (n > 1)
    {
        double tempSumation = 0;
        // calculating the sum of squared differences from the mean
        for (i = 0; i < n; i++)
            tempSumation += pow((inputNumber[i] - tempAverage), 2.0);

        // Calculating sample standard deviation
        tempStandardDeviation = sqrt(tempSumation / (n - 1));
    }

    // Assigning final values back to the variables in main().
    *sum = tempSum;
    *average = tempAverage;
    *standardDeviation = tempStandardDeviation;
}