Problems with code

Question

I create a program that calculates the products of a series of numbers."k" we type from the keyboard.I also do not understand how to find factorial in my incident.Help me please with the implementation
My code
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main()
{
int n,k;
float z,prd=1;
printf("Enter k: \n");
scanf("%d",&k);
for(n=-3;n<=k;n++)
{
z=((n+2)*(abs(n-4))/(n+3); // (n+3)!(factorial)
prd*=z //product of numbers
}
printf("5.2f \n",prd);
return 0;
}

Answer 1

Alright. That product is 0 as soon as n is -2.
But still, to calculate the factorial you can either write a simple algorithm yourself. Can look like this:

int factorial(int n)
{
int f = 1;
while(n) f *= n--;
return f;
}

But that means to repeat a lot of computations. It'd be smarter to produce the factorial as a side-effect of the loop.

A thing to remember: When dividing integers it will be integer division (division with remainder). To get floating points, you first need to convert one element to a floating point type (explicit type cast). So, the loop could look like this:

double prod = 1.0;
int f = 1;
for(int n=-3; n<=k; n++) {
prod *= ((double)(n+2) * abs(n-4)) / f;
f *= n+4;
}

Edit:
Just in case the product is supposed to be a sum (which would make more sense to me...):
double z = 0;
int f = 1;
for(int k=-3; k<n; k++) {
z += ((double)(k+2) * abs(k-4)) / f;
f *= k+4;
}

Answer 2

Could you write out the series you want to calculate without using "code" ? Right now, as soon as n is -2 one factor becomes zero. That means your product will become zero. [I understand that the denominator is supposed to be factorial, right? Otherwise you run into trouble there as well, dividing by 0...]

Answer 3

I am sorry, that makes even less sense than before. Now, you are trying to take the factorial of a negative number which isn't defined.

The k-th term is
(k+2) |k-4| / (k-4)! or
(k+2) |k-4| / (k+3)! ?

And the product runs from k=-3 up to n ?

Answer 4

thank you,Leif!

Answer 5

z=П k up,n=-3 down below (n+2)|n-4|/(n-4)!

Answer 6

https://photos.app.goo.gl/4sf5vi6PMXiCcnJk6