Error using for_each and lambda - c++

Question

I am trying to solve a simple Fibonacci problem using the lambda function, but I came across this error and I cant solve it.
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
string str;
auto N{0};
auto i{0};
cout<<"Digite o valor de N desejado: ";
getline(cin,str); //pega linha
stringstream(str) >> N;
if (N == 0){cout<<0;}
else if (N == 1){cout<<1;}
else
{
vector<int> v{0,1}; //cria vetor v
for_each(v.begin(),N,
[&](){
v.push_back(v[i]+v[i+1]);
i++;
});
i = 0;
for_each(v.begin(),N,
[&](){
cout<<v[i];
i++;
});
}
return 0;
}
And the error is the following:
quest1.cpp: In function ‘int main()’: quest1.cpp:30:4: error: no matching function for call to ‘for_each(std::vector<int>::iterator, int&, main()::<lambda()>)’ });
^ In file included from /usr/include/c++/6.3.1/algorithm:62:0,
from quest1.cpp:5: /usr/include/c++/6.3.1/bits/stl_algo.h:3763:5: note: candidate: template<class _IIter, class _Funct> _Funct std::for_each(_IIter,
_IIter, _Funct)
for_each(_InputIterator __first, _InputIterator __last, _Function __f)
^~~~~~~~ /usr/include/c++/6.3.1/bits/stl_algo.h:3763:5: note: template argument deduction/substitution failed: quest1.cpp:30:4: note: deduced conflicting types for parameter ‘_IIter’ (‘__gnu_cxx::__normal_iterator<int*, std::vector<int> >’ and ‘int’) });
^ quest1.cpp:38:5: error: no matching function for call to ‘for_each(std::vector<int>::iterator, int&, main()::<lambda()>)’
});
^ In file included from /usr/include/c++/6.3.1/algorithm:62:0,
from quest1.cpp:5: /usr/include/c++/6.3.1/bits/stl_algo.h:3763:5: note: candidate: template<class _IIter, class _Funct> _Funct std::for_each(_IIter,
_IIter, _Funct)
for_each(_InputIterator __first, _InputIterator __last, _Function __f)
^~~~~~~~ /usr/include/c++/6.3.1/bits/stl_algo.h:3763:5: note: template argument deduction/substitution failed: quest1.cpp:38:5: note: deduced conflicting types for parameter ‘_IIter’ (‘__gnu_cxx::__normal_iterator<int*, std::vector<int> >’ and ‘int’)
});

Answer 1

There's two problems in your code. One (already covered by other answers), you're passing the number of iterations as the second parameter to std::for_each, but it actually expects an end iterator. std::for_each(a, b, f) is designed to iterate from iterator a to iterator b and call f on each element in that range.
The second problem is more fundamental: if you modify the vector while iterating over it, you'll get Undefined Behaviour because any modification operation invalidates all iterators to the vector.
Looking at your code, it seems you want the first loop to a normal counting loop and not iteration over the container. The second loop could be done with for_each and a lambda:
vector<int> v{0,1};
for (int i = 0; i < N; ++i) {
v.push_back(v[i] + v[i+1]);
}
for_each(v.begin(), v.end(),
[](int element) {
cout << element;
}
);
Notice that the functor used in for_each is not nullary: the algorithm will pass the element to it.
Alternatively, the printing functionality could be implemented without lambdas:
copy(v.begin(), v.end(), ostream_iterator<int>(cout));
Or, if you prefer to keep the loop, you could just as well use a range-based for loop instead of for_each. The code will be shorter and [subjective]easier to read[/subjective]:
for (int elem : v) {
std::cout << elem;
}

Answer 2

std::for_each requires (as the error tries to tell you) an iterator where to start looping and an iterator where to end. You however are passing an iterator and an int, which are "conflicting types". If you want to loop over an whole vector do something like that:
std::vector<int> v{1, 2, 3};
std::for_each(v.begin(), // start at the front
v.end(), // loop over each element
[&] (int& i) {
i++;
});
If you just need to loop over a part of the vector do that
std::vector<int> v{1, 2, 3};
std::for_each(v.begin(), // start at the front
v.begin() + 2, // loop over the first two elements
[&] (int& i) {
i++;
});

Answer 3

You are not using the for_each function correctly. C++ does not know the signature you are using. Please refer to the documentation, e.g. for_each.
The compiler says exactly that. The second parameter of the for_each you are calling is of type int&, but the signature is for_each(InputIterator, InputIterator, Function) and not for_each(InputIterator, int&, Function), so it fails to compile.