#include <stdio.h>
#include <stdlib.h>

void print_vector(const double* vector, int n)
{
	putchar('<');
	int i = 0;
	for ( ; i < n - 1; ++i )
		printf("%.1lf, ", vector[i]);
	printf("%.1lf>", vector[i]);
}

double dot_product(const double v1[], const double v2[], int n)
{
	double result = 0.0;
	for ( int i = 0; i < n; ++i )
		result += v1[i] * v2[i];
	return result;
}

// Optional: do not declare local variables in body
void print_vector2(const double* vector, int n)
{
	putchar('<');
	while ( --n > 0 )
		printf("%.1lf, ", *vector++);
	printf("%.1lf>", *vector);
}

// Example: calculate dot product using pointer arithmetic without [] operator
double dot_product2(const double* v1, const double* v2, int n)
{
	double result = 0.0;
	while ( n-- )
		result += *v1++ * *v2++;
	return result;
}

// Calculates dot product of two vectors of real numbers given by argument
// An even quantity of real numbers are required, the program slices them in
// two arrays. If program is called with only one number by argument, nothing
// is done. With an odd quantity of numbers, the last one is ignored
int main(int argc, char* argv[])
{
	if ( argc <= 2 ) return 0;
	double values[argc - 1];
	for ( int i = 1; i < argc; ++i )
		values[i - 1] = atof( argv[i] );

	int n = (argc - 1) / 2; // if n was argc / 2, program could crash
	print_vector(values, n); printf(" * "); print_vector(values + n, n);
	printf(" = %.2lf\n", dot_product(values, values + n, n) );
	return 0;
}