want to add an integer in all the indexes of the integer array

Question

i want to add an integer in the all indexes of an array .without using loop .in single ststement.

int a[4]={4,4,4,4}; i want to add 1 in all indexes.. so the out put is cout<

output:_ 5 5 5 5

i relly thnks to all..

"without using loop .in single ststement" - sounds like an artificial requirement. What exactly you are trying to do? — Juliano
– Juliano, Commented Dec 26, 2010 at 17:28
I did it without using loops in one line see my answer below — user379888
– user379888, Commented Dec 28, 2010 at 15:32

zeuxcg · Accepted Answer · 2010-12-26 17:31:14Z

8

#include <functional>
#include <algorithm>

int main()
{
    int a[] = {1, 2, 3, 4};

    std::transform(a, a + sizeof(a) / sizeof(a[0]), a, std::bind1st(std::plus<int>(), 1));
}

answered Dec 26, 2010 at 17:31

zeuxcg

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6 Comments

Jonathan Grynspan Over a year ago

This is such a roundabout way of obfuscating the loop. +1!

moinudin Over a year ago

OP's question aside, when would one ever, ever, ever find this useful in practice over a loop? :P

zeuxcg Over a year ago

@marcog, well, true, in C++ it's better to use loops for trivial tasks :) in other languages though this is natural (i.e. in F# this would be a |> Array.map ((+) 1)).

Loki Astari Over a year ago

@ marcog: I find it rare that I ever actually write loops to do this kind of thing. One of the std::algorithms is nearly always my choice. As they are correct concise and tend to be highly optimizeable by the compiler.

David Rodríguez - dribeas Over a year ago

@marcog: There is a direct relation between how much you use a feature and how obscure it looks. I bet that in a couple of years, with lambdas added to the language, you will find this type of solution common, if expressed differently: std::transform( a, a+4, a, []( int x ) { return x+1; } );

|

Jerry Coffin · Accepted Answer · 2011-02-21 18:31:24Z

2

Yet another possibility would be to use an std::valarray:

int aa[] = {4, 4, 4, 4};

std::valarray<int> a(aa, 4);

a += 1;

I can't say I'd really recommend this, but it does work.

answered Feb 21, 2011 at 18:31

Jerry Coffin

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13 Comments

Fred Nurk Over a year ago

Why would you give an answer you don't recommend?

Jerry Coffin Over a year ago

@Fred Nurk: Because I think it's as good an answer as any to a silly question.

Fred Nurk Over a year ago

Why should silly questions get any answers? Joke answers (though yours isn't nearly as bad as some I've seen) are fun, but noise, especially in the cases where later clarification is given or someone figures out what the OP really means.

Fred Nurk Over a year ago

Maybe a different tack will illustrate what I'm trying to say: "I can't say I'd really recommend this, but it does work." has the same problem as "I can't say I'd really recommend stabbing yourself with a samurai sword, but it does work to get you into the emergency room quickly to have that toothache looked at." That isn't advice I'd give anyone, except in jest. I've never thought of you as one who gives answers purely for amusement.

Fred Nurk Over a year ago

Joke answers where people upvote for "This is such a roundabout way of obfuscating the loop. +1!" (that comment is itself at +2 currently) just make fun of the OP and the question (I did say yours isn't nearly as bad as some I've seen, but I also believe it was submitted in good faith unlike the really bad ones). Perhaps that pointing and laughing of the OP is deserved, perhaps not, but I don't think it makes a good answer.

|

Matthieu N. · Accepted Answer · 2010-12-27 06:39:00Z

1

How about doing it recursively:

template<typename Itr>
void inc(Itr itr, Itr end)
{
   if (itr == end) return;
   ++(*itr);
   inc(++itr,end);
}

int main()
{
   int a[4]={4,4,4,4}; 
   inc(a,a + 4);
   return 0;
}

This is tail-recusive, so a decent compiler should convert this into a loop.

answered Dec 27, 2010 at 6:39

Matthieu N.

Comments

Paul R · Accepted Answer · 2010-12-27 21:09:22Z

1

SSE2 solution (using intrinsics):

__m128i v1 = _mm_set_epi32(4, 4, 4, 4);
__m128i v2 = _mm_set_epi32(1, 1, 1, 1);
__m128i v3 = _mm_add_epi32(v1, v2);

answered Dec 27, 2010 at 21:09

Paul R

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Comments

user379888 · Accepted Answer · 2010-12-28 15:30:37Z

1

#include <iostream>
using namespace std;
int main()
{
int a[4]={4,4,4,4};
a[0]++,a[1]++,a[2]++,a[3]++;
return 0;
}

answered Dec 28, 2010 at 15:30

user379888

2 Comments

thecoshman Over a year ago

To those who have down voted this, please explain why. please also note that in C++ two operations separated by a , are not considered two separate operations.the , operator chains this together. Whilst this may not be the nicest looking solution, and definitely not scalable it dam well fits the question

Fred Nurk Over a year ago

They are separate operations, but not separate statements, which is (for unknown reasons) important to the OP.

Community · Accepted Answer · 2017-05-23 11:52:37Z

0

If your array can only have 4 elements, you might be able to use the PADDD instruction of the SSE2 instruction-set extension. I have never used this, so i cannot provide more details.

This question might give you more hints on how to do it.

edited May 23, 2017 at 11:52

CommunityBot

11 silver badge

answered Dec 26, 2010 at 18:03

anatolyg

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