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Why do arrays start at 0?

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Re: Why do arrays start at 0?

#121

Post by copperx »

HarHarVeryFunny wrote: post #100
hougaard wrote: post #14

It really comes down to a choice between a machine-focused (0) or human-focused (1) approach. The 0 makes a lot of sense in a C pointer world where memcpy and other alike functions can be written very thight. The 1 makes a lot of sense in a human world, when we count, we start at 1, we talk about the "1st", counting on finger starts with 1, etc. I once were at a Lua (1 indexed language) conference where this was disc…

Yes, but "human-focused" 1-based indexing comes at a cost since at the end of the day the CPU has to add (index * element-size) to the array base address to get the address of the indexed element. With a 1-based index there's additional overhead in either having to subtract 1 from the index or to have a wasted "element 0" to avoid the need to do that.

I assure you, that if we counted from zero, there would be an instruction to add and multiply in the same number of cycles as a multiply.

Re: Why do arrays start at 0?

#123

Post by xxs »

hougaard wrote: post #14

It really comes down to a choice between a machine-focused (0) or human-focused (1) approach. The 0 makes a lot of sense in a C pointer world where memcpy and other alike functions can be written very thight. The 1 makes a lot of sense in a human world, when we count, we start at 1, we talk about the "1st", counting on finger starts with 1, etc. I once were at a Lua (1 indexed language) conference where this was disc…

I have used 1 based in basic/pascal and 0 based (well in pretty much everything), 0 based effectively no off-by one mistakes. 1 based - common. Most idioms - incl. forward and reverse iterations work better, and are easier to remember with inclusive/exclusive pattern

Other than that - binary AND and power of 2 sized arrays are the backbone of any hashtable. Overall modulus (binary AND) is actually useful.

Re: Why do arrays start at 0?

#124

Post by luispauloml »

co_dh wrote: post #106
hougaard wrote: post #14

It really comes down to a choice between a machine-focused (0) or human-focused (1) approach. The 0 makes a lot of sense in a C pointer world where memcpy and other alike functions can be written very thight. The 1 makes a lot of sense in a human world, when we count, we start at 1, we talk about the "1st", counting on finger starts with 1, etc. I once were at a Lua (1 indexed language) conference where this was disc…

Human makes a lot of inconsistent thing: We usually think the 1st floor, and the basement as 1st underground floor ( -1), but the floor jumps from 1 to -1! Also, the time jump from 11AM to 12PM to 1PM! So I think more human friendly sometimes means more confusing.

That's true. But as for floor numbering, specifically, it depends on the country: some places have a "ground floor" between the 1st underground floor and the 1st "above ground" floor.

Re: Why do arrays start at 0?

#125

Post by ncmncm »

bluetomcat wrote: post #120
twanvl wrote: post #45

Other advantages of zero based indexing, beyond being 'closer to the machine': It works better with the modulo operator: `array[i%length]` vs `array[(i+length-1)%length+1]`. Or you would have to define a modulo-like operator that maps ℕ to [1..n]. It works better if you have a multi-dimensional index, for example the pixels in an image. With 0 based indexing, pixel `(x,y)` is at `array[x+width y]`. With 1 based index…

A disadvantage comes to mind. While the following loop works as expected: for (size_t i = 0; i The following causes an unsigned integer underflow and is an infinite loop: for (size_t i = length - 1; i >= 0; i--) ...

If you have foolishly turned off -W in your build system, that could happen. Otherwise, you get a nice warning pointing out your folly.

Re: Why do arrays start at 0?

#128

Post by gumby »

yongjik wrote: post #95
randomdata wrote: post #19

Earlier quoted context omitted.

> when we count, we start at 1, we talk about the "1st" Although often with an implicit zero. Under typical North American culture, your 1st birthday, for example, is more accurately the first anniversary of your birthday. Your birth is zero indexed.

That's why I prefer the Superior(TM) Korean age counting. You are one year old when you're born (it's your first year!). You are two year old on the next New Year's day. (Congratulations, it's your second your now!) So, if you're born on December 31st, you're two years old the next day. (I see no problem, but apparently some people are hung up on such minor details. I can't fathom why.)

This system is used for racehorses as well.

Re: Why do arrays start at 0?

#130

Post by xxs »

brianzelip wrote: post #31
atwood22 wrote: post #25

Earlier quoted context omitted.

No, birthdays are 1 indexed. Your Nth birthday is the day you turn N years old. When you're 1 year old, you've been alive for 1 year, not 2 years.

So how old is a not-yet-1-year old?

Your mistake is using years - use milliseconds (or nanoseconds) when you wish to express a duration. Years don't even have the same duration/length (leap years, and leap seconds)
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