Why I can't use 'less than' operator(<) in for loop when decreasing

Question

1.22/5 (2 votes)

See more:

Hi, I guess it's really silly question but:
why --> for (int i = 1000; i >=1; i-=2) System.out.println(i); (Cmd prints i)

---> for (int i = 1000; i <=1; i-=2) System.out.println(i); (no errors, no printing on the screen)

Why when i input <= cmd doesn't react and don't display decreasing iteration ?

Thank you in addvance!

What I have tried:

for (int i = 1000; i <=1; i-=2)
for (int i = 1000; i <1; i-=2)

Posted 13-Sep-18 5:11am

Member 13983435

Updated 13-Sep-18 6:12am

Add a Solution

Comments

Bryian Tan 13-Sep-18 11:34am

think about it, initially, i will be 1000, there no way 1000 < 1

2 solutions

Solution 1

for (int i = 1000; i <=1; i-=2)
for (int i = 1000; i <1; i-=2)

Look at your code. You start off with i<1 being false so it does nothing

When you use the >= version, you don't abort immediately.

You need to rethink about the order for the inequality!

Posted 13-Sep-18 5:42am

W∴ Balboos, GHB

Comments

Member 13983435 13-Sep-18 12:02pm

In both cases cmd doesn't print nothing
for (int i = 1000; i <=1; i-=2)
for (int i = 1000; i <1; i-=2)
...and I wonder why?
What I realize is that when we have i++ need to use < and when i-- we need to use > sign. Only then the program is printed .
But I still don't understand why exactly.

Dave Kreskowiak 13-Sep-18 12:16pm

You're just following a visual pattern, but you have no understanding of what each piece of the "for" statement does.

A "for" statement says this:

    for( initializer; bail out condition; step )

Using your 1st loop as an example:

1. Start with i having a value of 1000.
2. If i is less than or equal to 1, run the code in the loop, otherwise exit the loop.
3. When the code in the loop is finished, decrement i by 2.
4. Go back to step 2.

The loop doesn't do anything because i is greater than 1. The code in the loop is never executed.

Your second loop:
1. Start with i having a value of 1000.
2. If i is less than 1, run the code in the loop, otherwise exit the loop.
3. When the code in the loop is finished, decrement i by 2.
4. Go back to step 2.

Same problem. The value of i is greater than 1, not less than, so the code in the loop is never executed.

Member 13983435 13-Sep-18 12:19pm

I didn't know the loop works like that :) now I know and thank you so much for that

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Peter Leow · Accepted Answer · 2018-09-13T06:12:00

Solution 2

First, study this Flow of Execution of the for Loop[^]
in the case of

for (int i = 1000; i <=1; i-=2) System.out.println(i);

1. Initialization: i is initialized to 1000, i.e. i=1000, then it proceeds to 2;
2. Condition: the outcome of i <= 1, i.e. 1000 <= 1, is False, exit the loop, as such

System.out.println(i);

will never be executed.

Posted 13-Sep-18 6:12am

Peter Leow

Comments

Member 13983435 13-Sep-18 12:15pm

I see, that make sense
Thank you very much for the quick response (Y)