How to sum up elements of a C++ vector?

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What are the good ways of finding the sum of all the elements in a std::vector?

Suppose I have a vector std::vector<int> 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?

Actually there are quite a few methods.

int sum_of_elems = 0;
C++03
  1. Classic for loop:

    for(std::vector<int>::iterator it = vector.begin(); it != vector.end(); ++it)
        sum_of_elems += *it;
    
  2. Using a standard algorithm:

    #include <numeric>
    
    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
  1. b. Automatically keeping track of the vector type even in case of future changes:

    #include <numeric>
    
    sum_of_elems = std::accumulate(vector.begin(), vector.end(),
                                   decltype(vector)::value_type(0));
    
  2. Using std::for_each:

    std::for_each(vector.begin(), vector.end(), [&] (int n) {
        sum_of_elems += n;
    });
    
  3. Using a range-based for loop (thanks to Roger Pate):

    for (auto& n : vector)
        sum_of_elems += n;
    

Python program to find the sum of all elements of an array, How do you sum all elements in an array Python? Logic to find sum of array elements. Input size and elements in array , store in some variable say n and arr[n] . To store sum of array elements, initialize a variable sum = 0 . Note: sum must be initialized only with 0. To find sum of all elements, iterate through each element and add the current

The easiest way is to use std:accumuate of a vector<int> A:

#include <numeric>
cout << accumulate(A.begin(), A.end(), 0);

Sum of Numbers C++, not need a loop at all, just use the formula n*(n+1)/2 . We shall use a loop and sum up all values of the array. Algorithm. Let's first see what should be the step-by-step procedure of this program − START Step 1 → Take an array A and define its values Step 2 → Loop for each value of A Step 3 → Add each element to 'sum' variable Step 4 → After the loop finishes, display 'sum' STOP

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<int> vec
    private int sum

    public UberVector():
        vec = new Vector<int>()
        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 >= 0 and idx < 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.

How to sum up elements of a C++ vector?, Actually there are quite a few methods. int sum_of_elems = 0;. C++03. Classic for loop: for(std::vector<int>::iterator it = vector.begin(); it != vector.end(); ++it)  Method 2: Sum of array elements using pointers Here we are setting up the pointer to the base address of array and then we are incrementing pointer and using * operator to get & sum-up the values of all the array elements.

Why perform the summation forwards when you can do it backwards? Given:

std::vector<int> 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 > 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 > 0; --i)
    sum_of_elements += v.at(i-1);

We can use reverse iterators in a for loop:

for(std::vector<int>::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<int>::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(), [&](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.

Program to find sum of elements in a given array, Program to find sum of elements in a given array. Given an array of integers, find sum of its elements. function to return sum of elements Find four elements a, b, c and d in an array such that a+b = c+d · Find elements which are present in  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.

#include<boost/range/numeric.hpp>
int sum = boost::accumulate(vector, 0);

Program to calculate sum of array in C, Program to calculate sum of array in C. Algorithm. Let's first see what should be the step-by-step procedure of this program − START Step 1 → Take an array A and define its values Step 2 → Loop for each value of A Step 3 → Add each element to 'sum' variable Step 4 → After the loop finishes, display 'sum' STOP. In this post, we will discuss how to calculate sum of all elements in an integer array in C#. 1. Enumerable.Sum Method We can make use the build-in numeric aggregation method Sum() from the System.Linq Namespace to compute the sum of numeric values in a sequence. This is demonstrated below: [crayon-5ef52b48e2968370220204/] 2. …

How to sum up elements of a C++ vector?, How to sum up elements of a C++ vector? C++Server Side Programming​Programming. Sum up of all elements of a C++  code. /* C Program to find sum of elements. in a given array */. #include <bits/stdc++.h>. // function to return sum of elements. // in an array of size n. int sum ( int arr [], int n) {. int sum = 0; // initialize sum.

C Program to find sum of array elements using pointers, recursion , C Program to find sum of array elements using pointers, recursion & functions Here we are setting up the pointer to the base address of array and then we are  In this C Program to find sum of each row in a Matrix demo, User inserted values are: a [3] [3] = { {10, 20, 30}, { 12, 22, 32}, {44, 55, 121}} Row First Iteration: for (rows = 0; rows < 3; 0++) The condition (0 < 3) is True. Sum = 0. Column First Iteration: for (columns = 0; 0 < 3; 0++) The condition (0 < 3) is True.

C Program To Find Sum Of All Array Elements, As you can see, 5 elements are present in this array. Each element has been given the location a[0] to a[4]. Thus, adding up all the elements would give us: Sum  C# Sum Method: Add up All Numbers. Use the Sum extension method and the selector overload. Include the System.Linq namespace. Sum. This method adds up all values in an IEnumerable. It computes the sum total of all the numbers in an array, or List, of integers. This extension method in LINQ provides an excellent way to do this with minimal calling code.

Comments
  • "How many"? Really? That seems an overly vague question. :p Might be more useful to ask for a good way to do it.
  • What do you mean when you say "function similar to?" Are you looking for a replacement for std::accumulate in Boost? (If so, why?) Are you looking for functions that do something similar to std::accumulate? (If so, what?)
  • If you want something similar to std::accumulate, presumably you also want it to be different in some respect (otherwise you could just use std::accumulate); what difference(s) from std::accumulate are you looking for?
  • Of course in C++03 you can use std::for_each with a functor, it just takes more lines of code to define than the C++0x lambda.
  • Why do your lambda examples use for_each? accumulate would be more concise (even if it doesn't need the lambda)
  • @jalf: your point is correct, I should have used accumulate inside for_each but isn't this example useful(for learning purpose) as it shows that we can also have nested lambdas :-)
  • Be careful with accumulate. The last argument's type is used not just for the initial value, but for the type of the result. If you put an int there, it will accumulate ints even if the vector has float. The result can be subtly wrong, and the compiler will cast the result back up to a float without telling you.
  • Why would you use for_each if you have accumulate?
  • interesting, but be careful as std::vector isn't meant for subclassing.
  • Sorry, I should have been clearer - you could create your own class with the same methods as vector which maintained a has-a vector within it, rather than being a proper subclass (is-a).