For-loop stament confusion

Question

Hello,

I'm confused as to why the +=7 can't be put inside the initial parantheses () but has to be put inside the brackets {} to to succeed the exercise?

The snail climbs up 7 feet each day and slips back 2 feet each night.
How many days will it take the snail to get out of a well with the given depth?

Sample Input:
31

Sample Output:
6

Explanation: Let's break down the distance the snail covers each day:
Day 1: 7-2=5
Day 2: 5+7-2=10
Day 3: 10+7-2=15
Day 4: 15+7-2=20
Day 5: 20+7-2=25
Day 6: 25+7=32
So, on Day 6 the snail will reach 32 feet and get out of the well at day, without slipping back that night.

function main() {
var depth = parseInt(readLine(), 10);
//your code goes here

day = 0;

distance = 0;

for(; distance < depth; ) {

day ++

distance +=7

if(distance >= depth ) {break }

distance -= 2;
}

console.log(day );
}

Answer 1

Opposite. It's because the distance -= 2 is after the break. It MIGHT NOT happen because the break could happen and end the loop.

for(; distance < depth; ) {
day++
distance +=7 //7, 12, 17, 22, 27, 32
if(distance >= depth ) {break }
distance -= 2 //5, 10, 15, 20, 25 (30 doesn't happen because 32 >= depth and break.)

Answer 2

SuperKitsune94 The -7? I don't understand. But the difference is the step

If you place distance += 7 in the for loop. It will be -2+7.
But if you place it like in the description. It will be 7-2.
The result appears to be the same, but the point is subtracting 2 MIGHT NOT happen if the snail moving over the depth by adding to 7.

In -2+7, subtracting 2 definitely happen.
but it isn't in 7-2 where it might not, which is the algorithm of the correct program.

Like in the sample input 31, -2 isn't applied in the last day.

Answer 3

Thank you for helping me CarrieForle you're a good one!

Answer 4

CarrieForle so basically the -2 is like an Else statement for when the break doesn't yet happen because distance is not yet >= depth??

Answer 5

CarrieForle So there is no more -2 happening after the break stops the loop, correct?

Answer 6

The distance will be first substract by 2 and then add to 7.
Assume the depth is 31.
Day 1: 0-2+7=5
Day 2: 5-2+7=10
Day 3: 10-2+7=15
Day 4: 15-2+7=20
Day 5: 20-2+7=25
Day 6: 25-2+7=30 **
Day 7: 30-2+7 = 35
Loop ended, result is 7. Not right according to your sample input

Answer 7

I passed the exercise. My question is about the placement of the -7? CarrieForle

Answer 8

I meant the +=7, my bad. Thank you for explaining CarrieForle but the -2 comes after the break..so that means distance would be in a permanent -2 state right? How does this still work if distance is in a permanent state of -2? Is

Answer 9

So can you write down how you would do this formula please? I need to see your logic in an actual example CarrieForle

Answer 10

Correct ✅