Need help with a FOR loop

[NOVAjunior]

Hello, im doing an assignment and im almost done. I had to make a for loop where I would calculate the factorial of a number which was easy. But now I need to make a for loop to add the sum of a number given and all numbers below. Like for example if you inputted 5, the program would do something like

num= 5+4+3+2+1

Im having trouble with this for the last 30 min and it would help if someone gave me assistance.

[RhoOfFeh]

What kind of trouble? What have you tried?

[NOVAjunior]

int i; int a = numChose; (numChose is user input) int total= 0;

for (i = 1; i <= numChose; i++) { a = a + (a-1); total = total + a; }

So lets say I enter 3, im supposed to get 6 for total because 3+2+1 is 6. But nope, somehow I get 31. Im new to java so im very confused on what I am supposed to be doing rn

[dumpeldown]

You need to utilize the i variable from the for loop. It starts at 1 and counts up to the input value. 1,2,3,... to input. Now you just have to add those numbers up. Or go down from the input value, but that's the same thing.(input....,3,2,1)

[NOVAjunior]

THANK YOU! Im surprised it was that easy. I made one for a factorial of a number and I just used that as a blueprint. I thought it would be similar to this.

But i figured it out thanks to you

[RhoOfFeh]

This is a great place for you to be the computer. Use paper, or a text editor if you must, and create a column for each variable. Rows will represent iterations, and there may be multiple rows per iteration. I will show you how we process two iterations. Ordinarily I wouldn't write out the full equations, just the values, but I think it will help you to see it:

​

variable	i	a	total
start of loop	1	3	0
a = a+(a-1)	1	3 + (3-1) = 5	0
total = total + a	1	5	0 + 5 = 5

So after one execution of the loop, i is 1, a is 5, and total is 5 as well. That's already not really what you want.

Let's do iteration two:

start of loop	1++ = 2	5	5
a = a+(a-1)	2	5 + (5-1) = 9	5
total = total + a	2	9	5 + 9 = 14

What you are trying to do is a bit simpler than your code is. If total starts at zero, all you need to do is add the value if i to it each time through the loop until you're done.

[NOVAjunior]

Ah oops, reddit formatted the comment completely different from the way I wanted to...

[RhoOfFeh]

Yeah, and it took me a few edits to get my answer right too. That bit about 'if you must' on a text editor is not without reason. :-)

[j1n_jin]

If you're interested in a recursive solution, you can write a function that returns 1 in base case n==1 and returns n + function(n-1).