Should one prefer STL algorithms over hand-rolled loops?

#include <string>
#include <iostream>
#include <boost/foreach.hpp>

int main()
{
    std::string hello( "Hello, world!" );

    BOOST_FOREACH( char ch, hello )
    {
        std::cout << ch;
    }

    return 0;
}

for (int i = 0; i < some_vector.size(); i++)
    if (some_vector[i] == NULL) some_other_vector[i]++;

int weighted_sum = 0;
for (int i = 0; i < a_vector.size(); ++i) {
  weighted_sum += (i + 1) * a_vector[i];  // Just writing something a little nontrivial.
}

for (vector<Child>::iterator iter = children.begin();
    iter != children.end();
    ++iter)
{
    iter->setFooCount(n);
}

for_each(children.begin(), children.end(), SetFooCount(n));

class SetFooCount
{
public:
    SetFooCount(int n) : fooCount(n) {}

    void operator () (Child& child)
    {
        child.setFooCount(fooCount);
    }

private:
    int fooCount;
};