How to use template functions in C++ - c++

Question

I'm currently doing a program which calculates the scalarProduct (Dot Product) using templates and I've run into a problem with two things.
One being: How to declare a template and call it from main.
Two being: How to pass Arrays to functions.
Any help is appreciated, thanks
// scalarProduct.cpp : Defines the entry point for the console application.
//
#include <iostream>
#include <math.h> /* sqrt */
using namespace std;
template<typename T>
void scalarProduct(T a[], T b[])
{
T a[3];
T b[3];
this->a[] = a;
this->b[] = b;
T axb;
T roota;
T rootb;
T result;
axb = ((a[0] * b[0]) + (a[1] * b[1]) + (a[2] * b[2]));
roota = sqrt((a[0] * a[0]) + (a[1] * a[1]) + (a[2] * a[2])); // the formula for the Euclidean length of the vector A.
rootb = sqrt((b[0] * b[0]) + (b[1] * b[1]) + (b[2] * b[2])); // the formula for the Euclidean length of the vector B.
result = axb / roota * rootb;
cout << "Result: " << result;
};
int main()
{
int a[3];
int b[3];
cout << "Enter A: " << endl; // Vector A Input
cout << "X:";
cin >> a[0];
cout << "Y:";
cin >> a[1];
cout << "Z:";
cin >> a[2];
cout << "Ennter B: " << endl; // Vector B Input
cout << "X:";
cin >> b[0];
cout << "Y:";
cin >> b[1];
cout << "Z:";
cin >> b[2];
scalarProduct(a[], b[]);
system("pause");
return 0;
}

Answer 1

For the template part of the question:
Heres the format for declaring and defining a template function:
template<compileTimeParameters>
returnType functionName(functionParameters) {
...;
}
and invoke it like this:
functionName<compileTimeParameters>(functionParameters);
For example, if you wanted a function that printed with cout whatever you gave it, go like this:
template<typename T>
void println(T value) {
std::cout << value << std::endl;
}
and invoke like this:
int main() {
//string
println<std::string>("yo yo yo print a newline");
//integer
println<int>(420);
//some other random type
println<myType>(someInstanceOfMyType);
}
And if the compiler can deduce the template parameters by the function parameters, you don't have to specify anything explicitly inside the <> brackets. For example:
int main() {
//compiler deduces that you are passing a const char[]
println("the compiler can figure out what I mean");
}

Answer 2

In scalarProduct() get rid of your local arrays a and b -- you are getting them from the parameters passed into the function. Also, scalarProduct is a function, not the method of a class, so there is no "this" to reference.
In main() just call:
scalarProduct(a, b);
It should work then.

Answer 3

Your problem is not with templates, but with C++ basics, like passing array to a function.
// scalarProduct.cpp : Defines the entry point for the console application.
//
#include <iostream>
#include <math.h> /* sqrt */
using namespace std;
template<typename T>
void scalarProduct(T a[], T b[])
{
/*
* remove this
T a[3];
T b[3];
this->a[] = a;
this->b[] = b;
*/
T axb;
T roota;
T rootb;
T result;
axb = ((a[0] * b[0]) + (a[1] * b[1]) + (a[2] * b[2]));
roota = sqrt((a[0] * a[0]) + (a[1] * a[1]) + (a[2] * a[2])); // the formula for the Euclidean length of the vector A.
rootb = sqrt((b[0] * b[0]) + (b[1] * b[1]) + (b[2] * b[2])); // the formula for the Euclidean length of the vector B.
result = axb / roota * rootb;
cout << "Result: " << result;
};
int main()
{
int a[3];
int b[3];
cout << "Enter A: " << endl; // Vector A Input
cout << "X:";
cin >> a[0];
cout << "Y:";
cin >> a[1];
cout << "Z:";
cin >> a[2];
cout << "Ennter B: " << endl; // Vector B Input
cout << "X:";
cin >> b[0];
cout << "Y:";
cin >> b[1];
cout << "Z:";
cin >> b[2];
//scalarProduct(a[], b[]);
scalarProduct(a, b);
system("pause");
return 0;
}
Also if you dealing with three dimensional points I think it would be a good idea to create struct Point or class Point. If you want your functions to deal with vectors, then use pointers or better std::vector.