# Thread: How does this work?

1. Registered User
Join Date
Apr 2012
Posts
1

## How does this work?

How does this work?

Hello, I have a little logic problem in my head. I was trying to understand how does this code work:

Code:
``` var power = function (base, exponent){
if (exponent === 0){
return 1;
}
else {
return base * power(base, exponent-1);
}
};

power(2,2);```
It is from a lesson. What I am trying to find out is that: we ave defined a function with parameters base and exponent. Now it returns 0 if exponent is 1. In other cases it returns base * base^(exponent-1) which is basically x*x to the power of exponent -1.

Now how does base*power(base,exponent-1) work because I have not defined any way in this code to calculate it. As in how does the code know that I am trying to multiply x*x*x...etc.

I do not know if this makes any sense to any of you but if someone could explain.

2. Registered User
Join Date
Mar 2011
Posts
1,252
It's a recursive function. It repeatedly calls itself, decrementing the value of 'exponent' by 1 with each call until exponent equals 0.

When you call power(2,2):
First time through:
return 2 * (power(2,1))
Second time through:
power(2,1)
return 2 * (power(2,0));
Third time through:
power(2,0)
return 1;
Which is returned to the call in the second time through to resolve to:
return 2 * (1);
Which is returned to the call in the first time through to resolve to:
return 2 * 2;
Which equals 4 - and returned as the correct answer.

There are currently 1 users browsing this thread. (0 members and 1 guests)

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•

"

"

## X vBulletin 4.2.2 Debug Information

• Page Generation 0.08585 seconds
• Memory Usage 2,834KB
• Queries Executed 15 (?)
Template Usage (33):
• (1)bbcode_code
• (1)footer
• (1)forumjump
• (1)forumrules
• (1)gobutton
• (2)memberaction_dropdown
• (1)navbar
• (1)navbar_moderation
• (1)navbar_noticebit
• (1)navbar_tabs
• (2)option
• (2)postbit
• (2)postbit_onlinestatus
• (2)postbit_wrapper
• (1)spacer_close
• (1)spacer_open
• (1)tagbit_wrapper

Phrase Groups Available (6):
• global
• inlinemod
• postbit
• posting
• reputationlevel
Included Files (26):
• ./global.php
• ./includes/class_bootstrap.php
• ./includes/init.php
• ./includes/class_core.php
• ./includes/config.php
• ./includes/functions.php
• ./includes/class_friendly_url.php
• ./includes/class_hook.php
• ./includes/class_bootstrap_framework.php
• ./vb/vb.php
• ./vb/phrase.php
• ./includes/functions_calendar.php
• ./includes/functions_bigthree.php
• ./includes/class_postbit.php
• ./includes/class_bbcode.php
• ./includes/functions_reputation.php
• ./includes/functions_notice.php
• ./packages/vbattach/attach.php
• ./vb/types.php
• ./vb/cache.php
• ./vb/cache/db.php
• ./vb/cache/observer/db.php
• ./vb/cache/observer.php

Hooks Called (72):
• init_startup
• friendlyurl_resolve_class
• init_startup_session_setup_start
• database_pre_fetch_array
• database_post_fetch_array
• init_startup_session_setup_complete
• global_bootstrap_init_start
• global_bootstrap_init_complete
• cache_permissions
• fetch_postinfo_query
• fetch_postinfo
• fetch_foruminfo
• global_state_check
• global_bootstrap_complete
• global_start
• style_fetch
• global_setup_complete
• strip_bbcode
• friendlyurl_clean_fragment
• friendlyurl_geturl
• forumjump
• cache_templates
• cache_templates_process
• template_register_var
• template_render_output
• fetch_template_start
• fetch_template_complete
• parse_templates
• notices_check_start
• notices_noticebit
• process_templates_complete
• friendlyurl_redirect_canonical
• bbcode_fetch_tags
• bbcode_create
• postbit_factory
• postbit_display_start
• postbit_imicons
• bbcode_parse_start
• bbcode_parse_complete_precache
• bbcode_parse_complete
• postbit_display_complete
• memberaction_dropdown
• tag_fetchbit_complete
• forumrules
• navbits
• navbits_complete