How to find the product of vector elements? [duplicate] - c++

Question

This question already has answers here:
C++ Multiplying elements in a vector
(3 answers)
Closed 3 years ago.
I have the following vector values: [2, 3, 7].
I want to output the product of the vector, as in 2*3*7 = 42.
I wrote some code for it but it doesn't appear to be working. I am new to C++, so I am not sure how to get the product of the values in a vector given any numeric vector of any size.
#include <bits/stdc++.h>
int main()
{
int n;
cin >> n;
vector<int> vec;
while (n--)
{
int temp;
cin >> temp;
vec.push_back(temp);
}
int total = 1;
total *= vec;
cout << vec << endl;
return 0;
}

Answer 1

Using std::accumulate, one can do
#include <numeric> // std::accumulate
#include <functional> // std::multiplies
const auto total = std::accumulate(vec.cbegin(), vec.cend(), 1, std::multiplies<int>{});
By wrapping into a templated function, the code would be more generic
template<typename Type>
auto product(const std::vector<Type>& vec, Type init)
{
return std::accumulate(vec.cbegin(), vec.cend(), init, std::multiplies<Type>{});
}
and call it with
const auto total = product(vec, /*value to be initialized/ started with*/);

Answer 2

With std, you might use std::accumulate:
int product(const std::vector<int>& v)
{
return std::accumulate(v.begin(), v.end(), 1, std::multiplies<>{});
}

Answer 3

Try multiplying each value inside the vector.
for(std::size_t i=0; i<vec.size(); i++) {
total *= vec[i];
}

Answer 4

Here is what I would do for your example:
#include <iostream>
int main ()
{
int n;
std::cin >> n;
int total = 1;
while(n--) {
int temp;
std::cin >> temp;
total *= temp;
}
std::cout << "Total: " << total << std::endl;
return 0;
}

Answer 5

My solution uses std::accumulate with the operator std::multiplies to accumulate all elements by multiplying them. By just modifying your code, the end result would be:
#include <bits/stdc++.h>
int main() {
int n;
std::cin >> n;
std::vector<int> vec;
while(n--) {
int temp;
std::cin >> temp;
vec.push_back(temp);
}
int result = std::accumulate(std::begin(vec), std::end(vec), 1, std::multiplies<int>());
std::cout << result << std::endl;
return 0;
}
You were not processing the vector at all, and also outputting the vector but not the total result.

Answer 6

If you want to get the product of any numeric vector of any size, here's a function that works with any numeric type of vector with the help of templates:
template <class any>
long double vectorProduct(vector<any> vec) {
long double total = 1;
for(any num : vec) {
total *= num;
}
return total;
}
Usage:
cout << vectorProduct(vec) << endl;