 # accumulate  Category: algorithms Component type: function

### Prototype

Accumulate is an overloaded name; there are actually two accumulate functions.
```template <class InputIterator, class T>
T accumulate(InputIterator first, InputIterator last, T init);

template <class InputIterator, class T, class BinaryFunction>
T accumulate(InputIterator first, InputIterator last, T init,
BinaryFunction binary_op);
```

### Description

Accumulate is a generalization of summation: it computes the sum (or some other binary operation) of init and all of the elements in the range [first, last). 

The function object binary_op is not required to be either commutative or associative: the order of all of accumulate's operations is specified. The result is first initialized to init. Then, for each iterator i in [first, last), in order from beginning to end, it is updated by result = result + *i (in the first version) or result = binary_op(result, *i) (in the second version).

### Definition

Defined in the standard header numeric, and in the nonstandard backward-compatibility header algo.h.

### Requirements on types

For the first version, the one that takes two arguments:
• InputIterator is a model of Input Iterator.
• T is a model of Assignable.
• If x is an object of type T and y is an object of InputIterator's value type, then x + y is defined.
• The return type of x + y is convertible to T.
For the second version, the one that takes three arguments:
• InputIterator is a model of Input Iterator.
• T is a model of Assignable.
• BinaryFunction is a model of Binary Function.
• T is convertible to BinaryFunction's first argument type.
• The value type of InputIterator is convertible to BinaryFunction's second argument type.
• BinaryFunction's return type is convertible to T.

### Preconditions

• [first, last) is a valid range.

### Complexity

Linear. Exactly last - first invocations of the binary operation.

### Example

```int main()
{
int A[] = {1, 2, 3, 4, 5};
const int N = sizeof(A) / sizeof(int);

cout << "The sum of all elements in A is "
<< accumulate(A, A + N, 0)
<< endl;

cout << "The product of all elements in A is "
<< accumulate(A, A + N, 1, multiplies<int>())
<< endl;
}
```

### Notes

 There are several reasons why it is important that accumulate starts with the value init. One of the most basic is that this allows accumulate to have a well-defined result even if [first, last) is an empty range: if it is empty, the return value is init. If you want to find the sum of all of the elements in [first, last), you can just pass 0 as init.

### See also

inner_product, partial_sum, adjacent_difference, count  Copyright © 1999 Silicon Graphics, Inc. All Rights Reserved. TrademarkInformation