cp16

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

int n, i, sum, task, x, y, fact;
float previous, current, sum_t = 0, t;

int sum3(int x, int y)
{
    sum = 0;
    for (i = x; i <= y; i++)
    {
        if (i % 2 == 0)
            sum += pow(i, 3);
    }
    return sum;
}

int factorial(int n)
{
    fact = 1;
    for (i = 1; i <= n; i++)
        fact *= i;
        if (fact == n)
        {
            printf("YES - %d!\n", i);
            return 0;
        }
    return 0;
}

double last(float x, int n)
{
    return powf(-1, n)*(n - 1)*powf(x, n)/(n + 1);
}

int main(void)
{
    printf("Choose the task: 1, 2 or 3:\n");
    scanf("%d", &task);
    if (task == 1)
    {
        printf("Enter the range [x,y]:\n");
        scanf("%d%d", &x, &y);
        printf("%d", sum3(x, y));
    }
    else if (task == 2)
    {
        printf("Enter the number N:\n");
        scanf("%d", &n);
        factorial(n);
    }
    else if (task == 3)
    {
        float x;
        printf("Enter the number x (|x| < 1):\n");
        scanf("%f", &x);
        t = 1;
        current = last(x, t);
        sum_t += current;
        //printf("%f %f\n", current, sum_t);
        t++;
        do
        {
            previous = current;
            current = last(x, t);
            sum_t += current;
            //printf("%f %f %f\n", previous, current, sum_t);
            t++;
        } while (fabs(current - previous) > pow(10, -4));
        printf("%f\n", sum_t);
    }
}