[Loop] [JavaScript] Factorial Fun Quesions

Question

Hi everyone,

I am troubled by this problem, please advice, many thanks😊

————————-
MY CODE

function main() {
var number = parseInt(readLine(), 10)
var factorial = 1;
// Your code here

for (vat i=0; i <=number; i++){
number * (number-i)
}
console.log(number)
}

———————

1. When two variables are set, which one is the var inside the For loop?
2. Ｉthought a “factorial” is the PRODUCT of all positive integers less than or equal to the number. Why set the variable to 1?

Answer 1

So factorial 5 = 1×2×3×4×5
Factorial 0 is 1

Your code needs to sum in the loop which number*(number-i) does not do in any language I am aware of 😉

Something like factorial *= i...

starting factorial at 1 overcomes the issue of returning 0 as the sum. 0x1x2x3x4x5=0

Answer 2

Please always tag the programming language.
https://code.sololearn.com/W3uiji9X28C1/?ref=app

Answer 3

In the for loop you have a typo. vat i=0 should be var=1

Answer 4

As to your questions:
1. The variable number holds the number for which you should calculate the factorial. It is the upper limit for the loop and determines the number of iterations. The variable factorial holds the result of each step of the calculation which after the last iteration of the loop is the result that you should output.
2. The value of factorial changes inside the loop. 1 is only the initial value, at the end the value of factorial is the factorial of number.

So here's what the program should do:
Take a number as input and assign it to the variable number.
Initialise the variable factorial setting it to 1.
Loop through the numbers 1 to number.
Inside the loop multiply the variable factorial by the loop variable.
After the last Iteration output the variable factorial.

Answer 5

So in your second example let's work through it...

number = 5
factorial = 1
Loop...
i =1
Pass 1
i = 1, number = 5, factorial = 1 x 5 = 5
Pass 2
i = 1, number = 4, factorial = 5 x 4 = 20
Pass 3
i = 1, number = 3, factorial = 3 x 20 = 60
Pass 4
i = 1, number = 2, factorial = 2 x 60 = 120
Pass 5
i<number is false loop terminates

Answer 6

Hi Simon Sauter,
Have changed the title, your answer is very knowledgeable and helpful, thanks!

Hi Paul K Sadler,
fixed the typo and got the idea of why starting factorial at 1, thank you!😄

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Both solutions work:
1.
function main() {
var number = parseInt(readLine(), 10)
var factorial = 1;
// Your code here
for ( i=1;i<= number; i++) {
factorial *= i;
}
console.log (factorial)
}

2.
function main() {
var number = parseInt(readLine(), 10)
var factorial = 1;
//Your code here
for ( i= 1; i < number; number--) {
factorial*=number;
}
console.log (factorial);
}

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But I have a further question now,
In the SOLUTION 2, why the statement 2 could be i=number or i<=number? They both work, but I don't get the logic behind it.

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And I've created a note for this question based on your answers, hope this can help people with similar problem. please visit

https://hackmd.io/@G0jOQteCSSeB-_fWD9vMgw/SJrqEvTNY

Answer 7

Hi Paul,

Thank you for your patience and careful explanation, as a beginner with a passion for programming, I understand the logic behind it better through your explanation!😊

Answer 8

OH, ok! But when I tried to add a new tag by editing my post, the system sent me back an error message. What should I do? Re-post the question?

Answer 9

Liangyong Peng if you can't add a tag just add the language to the title.