boost simple program problem

I have this small boost program ...

Code:

---

#include <boost/lambda/lambda.hpp>
#include <iostream>
#include <iterator>
#include <algorithm>

int main()
{
//    using namespace boost::lambda;
//    typedef std::istream_iterator<int> in;

    std::for_each(
        std::istream_iterator<int> in(std::cin),
        in(),
        std::cout << (boost::lambda::_1 * 3) << " "
    );
    return 0;
}

---

and when compiling under MSVC .Net 2003, it gives following errors:

Quote:

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Compiling...
test-bed.cpp
c:\my\src\cpp\test-bed\test-bed.cpp(267) : error C2275: 'std::istream_iterator<_Ty>' : illegal use of this type as an expression
with
[
_Ty=int
]
c:\my\src\cpp\test-bed\test-bed.cpp(267) : error C2146: syntax error : missing ')' before identifier 'in'
c:\my\src\cpp\test-bed\test-bed.cpp(269) : error C2059: syntax error : ')'

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Can someone explain this?

Well, i solved the errors, this is my new code:

Code:

---

#include <boost/lambda/lambda.hpp>
#include <iostream>
#include <iterator>
#include <algorithm>

int main()
{
    using namespace boost::lambda;
    using namespace std;
    typedef std::istream_iterator<int> in;

    cout << "Enter numbers, to stop enter Ctrl-Z:" << endl;
    int sum=0;
    std::for_each(
        in(cin),
        in(),
        sum += _1
    );
    cout << "Sum: " << sum << endl;
    return 0;
}

---

As can be seen, I can calculate the sum now, how to calculate the average here?

Well, you need to do an element count, too, so

Code:

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std::for_each(in(cin), in(), (sum += _1, ++count));

---

But I'm not sure if lambda actually overloads the comma operator.

I changed my code, as CornedBee told:

Code:

---

#include <boost/lambda/lambda.hpp>
#include <iostream>
#include <iterator>
#include <algorithm>

int main()
{
    using namespace boost::lambda;
    using namespace std;
    typedef std::istream_iterator<int> in;

    cout << "Enter numbers, to stop enter Ctrl-Z:" << endl;
    int sum=0, cnt=0;
    cout << for_each(
        in(cin),
        in(),
        (sum += _1,cnt++)
    );
    cout << "Sum: " << sum << " Average: " << (sum/cnt) << endl;
    return 0;
}

---

but does not work:

Code:

---

Input:
1 2 3 4 5
Output:
Sum: 15 Average: 15

---

Ah. , is overloaded, but the right side is not a lambda expression.

Try

Code:

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(sum += _1, ++boost::lambda::var(cnt))

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Works! :)
Thanks CornedBee.

How about just:

Code:

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sum = std::accumulate(in(cin), in());

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Won't give you the count.

Quote:

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Originally Posted by CornedBee

Won't give you the count.

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Ehh.. I'm not paying attention.