sum of square of each elements in the vector using for_each
- by pierr
Hi,
As the function accepted by for_each take only one parameter (the element of the vector), I have to define a static int sum = 0 somewhere so that It can be accessed
after calling the for_each . I think this is awkward. Any better way to do this (still use for_each) ?
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
static int sum = 0;
void add_f(int i )
{
sum += i * i;
}
void test_using_for_each()
{
int arr[] = {1,2,3,4};
vector<int> a (arr ,arr + sizeof(arr)/sizeof(arr[0]));
for_each( a.begin(),a.end(), add_f);
cout << "sum of the square of the element is " << sum << endl;
}
In Ruby, We can do it this way:
sum = 0
[1,2,3,4].each { |i| sum += i*i} #local variable can be used in the callback function
puts sum #=> 30
Would you please show more examples how for_each is typically used in practical programming (not just print out each element)? Is it possible use for_each simulate 'programming pattern' like map and inject in Ruby (or map /fold in Haskell).
#map in ruby
>> [1,2,3,4].map {|i| i*i}
=> [1, 4, 9, 16]
#inject in ruby
[1, 4, 9, 16].inject(0) {|aac ,i| aac +=i} #=> 30
EDIT: Thank you all. I have learned so much from your replies. We have so many ways to do the same single thing in C++ , which makes it a little bit difficult to learn. But it's interesting :)
