Reduce in C++

In C++, we can use the STL (Standard Template Library) algorithm std::accumulate to reduce an array to a single value.

Here is an example code:

``c++
#include
#include
using namespace std;

int main() {
int arr[] = { 1, 2, 3, 4, 5 };
int sum = accumulate(begin(arr), end(arr), 0);
cout << "Sum of array is " << sum << endl;
return 0;
}
`

In this code, we first declare an integer array arr with 5 values. We then use the std::accumulate function to calculate the sum of these values. The accumulate function takes three arguments: the beginning iterator of the array, the ending iterator of the array, and the initial value of the accumulation (which is 0 in this case).

The accumulate function returns the sum of all the values in the array, which we then print to the console using cout`.