A frequency function using template - c++

Question

I am trying to write a template-based function frequency that will return the count of the occurrences of an item in an array of items.
So far I have
#include <iostream>
using namespace std;
template <class T>
T frequency(T array[], T arraySize, T item) {
int count = 0;
for (int i = 0; i < arraySize; i++) {
if (array[i] == item) {
count++;
}
}
return count;
}
int main() {
// Testing template with int
int intArray[10] = { 1, 2, 3, 3, 14, 3, 2, 7, 99, 2 };
cout << "{ ";
for (int i = 0; i < 10; i++) {
cout << intArray[i] << " ";
}
cout << "}" << endl;
cout << "Frequency of 3: " << frequency(intArray, 10, 3) << endl;
cout << "Frequency of 2: " << frequency(intArray, 10, 2) << endl;
cout << "Frequency of 99: " << frequency(intArray, 10, 99) << endl;
// Testing template with double
double doubleArray[10] = { 1.5, 2.2, 99.4, 132.11, 1.5, 2.22, 1.515, 66.2, 51.8, 34.0 };
cout << "{ ";
for (int j = 0; j < 10; j++) {
cout << doubleArray[j] << " ";
}
cout << "}" << endl;
cout << "Frequency of 1.5: " << frequency(doubleArray, 10, 1.5) << endl;
cout << "Frequency of 2.2: " << frequency(doubleArray, 10, 2.2) << endl;
cout << "Frequency of 100.1: " << frequency(doubleArray, 10, 100.1) << endl;
return 0;
}
however, I get an error of "no matching function for call to 'frequency(double [10], int, double)'" towards when I try to print out the frequency of the doubles. I am unsure what I am doing wrong.
Thank you for any help!

Answer 1

frequency takes parameters of element of array and arraySize with the same type, i.e. T. But you pass arguments of that with different types, i.e. double vs int. Then the type deduction fails because T can't be deduced (determined).
According to your implemantaion, the type arraySize seems fixed, you can just declare it as std::size_t or int. And same for the return type. Their types won't change then shouldn't be declared with template parameters.
template <class T>
int frequency(T array[], std::size_t arraySize, T item) {
int count = 0;
for (std::size_t i = 0; i < arraySize; i++) {
if (array[i] == item) {
count++;
}
}
return count;
}

Answer 2

You should not use your template parameter with arraySize. Because you compare it with i, int i = 0; i < arraySize;. And the return type should not be T too because a double is not accurate don't use it like counter. Plus you do return count and you write int count = 0;
template <class T>
int frequency(T const array[], int arraySize, T const &item);
Be aware that the standard library has a template function to this purpose. In a production code, you should use std::count_if().
int count = std::count_if(intArray.begin(), intArray.end(), [](int i){ return i == 42; });

Answer 3

You can crate frequency as, so that it can be used with other containers.
#include <iostream>
#include <vector>
using namespace std;
template <class outputIterator,class T>
int frequency(outputIterator b,outputIterator e ,const T& v) {
int count = 0;
while(b != e)
{
if(*b == v)
{
count++;
}
b++;
}
return count;
}
int main ()
{
std::vector<int> first={1,1,2,3,4,5,5};
std::cout<<frequency(first.begin(),first.end(),1)<<std::endl;
int arr[]={1,2,3,5,5,5};
std::cout<<frequency(std::begin(arr),std::end(arr),5)<<std::endl;
return 0;
}