Multiply vector elements by a scalar value using STL

Modern C++ solution for your question.

#include <algorithm>
#include <vector>

std::vector<double> myarray;
double myconstant{3.3};
std::transform(myarray.begin(), myarray.end(), myarray.begin(), [&myconstant](auto& c){return c*myconstant;});

If you can use a valarray instead of a vector, it has builtin operators for doing a scalar multiplication.

v *= 3;

If you have to use a vector, you can indeed use transform to do the job:

transform(v.begin(), v.end(), v.begin(), _1 * 3);

(assuming you have something similar to Boost.Lambda that allows you to easily create anonymous function objects like _1 * 3 :-P)

Yes, using std::transform:

std::transform(myv1.begin(), myv1.end(), myv1.begin(),
               std::bind(std::multiplies<T>(), std::placeholders::_1, 3));

Before C++17 you could use std::bind1st(), which was deprecated in C++11.

std::transform(myv1.begin(), myv1.end(), myv1.begin(),
               std::bind1st(std::multiplies<T>(), 3));

For the placeholders;

#include <functional>