How to sum up elements of a C vector

Question

What are the good ways of finding the sum of all the elements in a std  vector   Suppose I have a vector std  vector lt int gt  vector with a few elements in it  Now I want to find the sum of all the elements  What are the different ways for the same

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C  0x only   vector lt int gt  v     and fill with data int sum        or   0        for  int n   v  sum    n    This is similar to the BOOST FOREACH mentioned elsewhere and has the same benefit of clarity in more complex situations  compared to stateful functors used with accumulate or for each

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One can also use std  valarray lt T gt  like this   include lt iostream gt   include lt vector gt   include lt valarray gt   int main         std  vector lt int gt  seq  1 2 3 4 5 6 7 8 9 10        std  valarray lt int gt  seq add  seq data    seq size          std  cout  lt  lt   sum      lt  lt  seq add sum    lt  lt    n        return 0      Some may not find this way efficient since the size of valarray needs to be as big as the size of the vector and initializing valarray will also take time   In that case  don t use it and take it as yet another way of summing up the sequence

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Actually there are quite a few methods   int sum of elems   0    C  03   Classic for loop   for std  vector lt int gt   iterator it   vector begin    it    vector end      it      sum of elems     it   Using a standard algorithm        include  lt numeric gt   sum of elems   std  accumulate vector begin    vector end    0     Important Note  The last argument s type is used not just for the initial value  but for the type of the result as well  If you put an int there  it will accumulate ints even if the vector has float  If you are summing floating-point numbers  change 0 to 0 0 or 0 0f  thanks to nneonneo   See also the C  11 solution below    C  11 and higher   b  Automatically keeping track of the vector type even in case of future changes     include  lt numeric gt   sum of elems   std  accumulate vector begin    vector end                                   decltype vector   value type 0     Using std  for each   std  for each vector begin    vector end      amp    int n        sum of elems    n       Using a range-based for loop  thanks to Roger Pate    for  auto amp  n   vector      sum of elems    n

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Why perform the summation forwards when you can do it backwards   Given   std  vector lt int gt  v         vector to be summed int sum of elements 0      result of the summation   We can use subscripting  counting backwards   for  int i v size     i  gt  0  --i      sum of elements    v i-1     We can use range-checked  subscripting   counting backwards  just in case    for  int i v size     i  gt  0  --i      sum of elements    v at i-1     We can use reverse iterators in a for loop   for std  vector lt int gt   const reverse iterator i v rbegin     i    v rend      i      sum of elements     i    We can use forward iterators  iterating backwards  in a for loop  oooh  tricky     for std  vector lt int gt   const iterator i v end     i    v begin    --i      sum of elements      i - 1     We can use accumulate with reverse iterators   sum of elems   std  accumulate v rbegin    v rend    0     We can use for each with a lambda expression using reverse iterators   std  for each v rbegin    v rend      amp   int n    sum of elements    n        So  as you can see  there are just as many ways to sum the vector backwards as there are to sum the vector forwards  and some of these are much more exciting and offer far greater opportunity for off-by-one errors

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It is easy  C  11 provides an easy way to sum up elements of a vector    sum   0   vector lt int gt  vec    1 2 3 4 5       for auto i vec      sum  i  cout lt  lt   The sum is      lt  lt sum lt  lt endl

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include lt boost range numeric hpp gt  int sum   boost  accumulate vector  0

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One more option which I did not notice in the answers is using std  reduce which is introduced in c  17  But you may notice many compilers not supporting it  Above GCC 10 may be good   But eventually the support will come  With std  reduce  the advantage comes when using the execution policies  Specifying execution policy is optional  When the execution policy specified is std  execution  par  the algorithm may use hardware parallel processing capabilities  The gain may be more clear when using big size vectors  Example    SAMPLE std  vector lt int gt  vec    2 4 6 8 10 12 14 16 18          WITHOUT EXECUTION POLICY int sum   std  reduce vec begin   vec end            TAKING THE ADVANTAGE OF EXECUTION POLICIES int sum2   std  reduce std  execution  par vec begin   vec end          std  cout  lt  lt   quot Without execution policy   quot   lt  lt  sum  lt  lt  std  endl  std  cout  lt  lt   quot With execution policy   quot   lt  lt  sum2  lt  lt  std  endl   You need  lt numeric gt  header for std  reduce  And   lt execution gt   for execution policies

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Prasoon has already offered up a host of different  and good  ways to do this  none of which need repeating here  I d like to suggest an alternative approach for speed however   If you re going to be doing this quite a bit  you may want to consider  sub-classing  your vector so that a sum of elements is maintained separately  not actually sub-classing vector which is iffy due to the lack of a virtual destructor - I m talking more of a class that contains the sum and a vector within it  has-a rather than is-a  and provides the vector-like methods    For an empty vector  the sum is set to zero  On every insertion to the vector  add the element being inserted to the sum  On every deletion  subtract it  Basically  anything that can change the underlying vector is intercepted to ensure the sum is kept consistent   That way  you have a very efficient O 1  method for  calculating  the sum at any point in time  just return the sum currently calculated   Insertion and deletion will take slightly longer as you adjust the total and you should take this performance hit into consideration   Vectors where the sum is needed more often than the vector is changed are the ones likely to benefit from this scheme  since the cost of calculating the sum is amortised over all accesses  Obviously  if you only need the sum every hour and the vector is changing three thousand times a second  it won t be suitable   Something like this would suffice   class UberVector      private Vector lt int gt  vec     private int sum      public UberVector            vec   new Vector lt int gt            sum   0      public getSum            return sum      public add  int val           rc   vec add  val          if rc    OK              sum   sum   val         return rc      public delindex  int idx           val   0         if idx  gt   0 and idx  lt  vec size              val   vec idx          rc    vec delindex  idx          if rc    OK              sum   sum - val         return rc   Obviously  that s pseudo-code and you may want to have a little more functionality  but it shows the basic concept

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I m a Perl user  an a game we have is to find every different ways to increment a variable    that s not really different here  The answer to how many ways to find the sum of the elements of a vector in C   is probably an infinity     My 2 cents   Using BOOST FOREACH  to get free of the ugly iterator syntax   sum   0  BOOST FOREACH int  amp  x  myvector     sum    x      iterating on indices  really easy to read    int i  sum   0  for  i 0  i lt myvector size    i       sum    myvector i       This other one is destructive  accessing vector like a stack   while   myvector empty        sum  myvector back       myvector pop back

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The easiest way is to use std accumulate of a vector lt int gt  A   include  lt numeric gt  cout  lt  lt  accumulate A begin    A end    0

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Nobody seems to address the case of summing elements of a vector that can have NaN values in it  e g  numerical limits lt double gt   quite NaN   I usually loop through the elements and bluntly check  vector lt double gt  x          size t n   x size     double sum   0   for  size t i   0  i  lt  n  i        sum     x i     x i    x i    0       It s not fancy at all  i e  no iterators or any other tricks but I this is how I do it  Some times if there are other things to do inside the loop and I want the code to be more readable I write double val   x i    sum     val    val   val   0           inside the loop and re-use val if needed

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include lt iostream gt       include lt vector gt       include lt numeric gt      using namespace std      int main            vector lt int gt  v    2 7 6 10          cout lt  lt  quot Sum of all the elements are  quot  lt  lt endl         cout lt  lt accumulate v begin   v end   0

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I found the most easiest way to find sum of all the elements of a   vector    include  lt iostream gt   include lt vector gt  using namespace std   int main         vector lt int gt v 10 1       int sum 0      for int i 0 i lt v size   i                  sum  v i             cout lt  lt sum lt  lt endl          In this program  I have a vector of size 10 and are initialized by 1  I have calculated the sum by a simple loop like in array

[c++] How to sum up elements of a C++ vector?

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