Question

How to implement vector inner product in C++

Answer 1

#include <iostream>  
#include <vector> 

using std::vector;
using std::cout;
using std::endl;

int inner_product(vector<int> v1, vector<int> v2)
{
	// (0*5)+(1*4)+(2*2)+(3*3)+(4*1) = 0 + 4 + 4 + 9 + 4 = 21

	int sum = 0;
	for (int i = 0; i < v1.size(); i++)
		sum += v1[i] * v2[i];

	return sum;
}

int main()
{
	vector<int> v1{ 0, 1, 2, 3, 4 }, v2{ 5, 4, 2, 3, 1 };

	cout << inner_product(v1, v2) << endl;

	return 0;
}

/*
run:

21

*/

 

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Answer 2

#include <iostream>  
#include <vector> 

using std::vector;
using std::cout;
using std::endl;

int inner_product(vector<int> v1, vector<int> v2)
{
	// (0*5)+(1*4)+(2*2)+(3*3)+(4*1) = 0 + 4 + 4 + 9 + 4 = 21

	int sum = 0;
	vector<int>::iterator i1 = v1.begin();
	vector<int>::iterator i2 = v2.begin();

	while (i1 != v1.end()) {
		sum += *i1 * *i2;
		i1++; i2++;
	}

	return sum;
}

int main()
{
	vector<int> v1{ 0, 1, 2, 3, 4 }, v2{ 5, 4, 2, 3, 1 };

	cout << inner_product(v1, v2) << endl;

	return 0;
}

/*
run:

21

*/

 

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