How to change parameter name? - c++

Question

First there is a vector with a size 20. We assign random numbers from 0 to 100 to the vector. Then, using the template function, we find the total, mean, median, and standard deviation of this vector's elements. The code is as follows and the screen output is below.
#include <numeric>
#include <cmath>
#include <algorithm>
#include <functional>
#include <vector>
#include <iostream>
#include <ctime>
#include <cstdlib>
using namespace std;
template<int N, class T>
T nthPower(T x) {
T ret = x;
for (int i=1; i < N; ++i) {
ret *= x;
}
return ret;
}
template<class T, int N>
struct SumDiffNthPower {
SumDiffNthPower(T x) : mean_(x) { };
T operator( )(T sum, T current) {
return sum + nthPower<N>(current - mean_);
}
T mean_;
};
template<class T, int N, class Iter_T>
T nthMoment(Iter_T first, Iter_T last, T mean) {
size_t cnt = distance(first, last);
return accumulate(first, last, T( ), SumDiffNthPower<T, N>(mean)) / cnt;
}
template<class T, class Iter_T>
T computeVariance(Iter_T first, Iter_T last, T mean) {
return nthMoment<T, 2>(first, last, mean);
}
template<class T, class Iter_T>
T computeStdDev(Iter_T first, Iter_T last, T mean) {
return sqrt(computeVariance(first, last, mean));
}
template<class T, class Iter_T>
void computeStats(Iter_T first, Iter_T last, T& sum, T& mean,
T& var, T& std_dev)
{
size_t cnt = distance(first, last);
sum = accumulate(first, last, T( ));
mean = sum / cnt;
var = computeVariance(first, last, mean);
std_dev = sqrt(var);
}
int RandomNumber () { return (std::rand()%100); }
int main(int argc, char **argv) {
std::srand ( unsigned ( std::time(0) ) );
vector<int> v(20);
std::generate (v.begin(), v.end(), RandomNumber);
double sum, mean, var, dev;
computeStats(v.begin( ), v.end( ), sum, mean, var, dev);
cout << "count = " << v.size( ) << "\n";
cout << "sum = " << sum << "\n";
cout << "mean = " << mean << "\n";
cout << "variance = " << var << "\n";
cout << "standard deviation = " << dev << "\n";
cout << endl;
}
Output is:
count = 20
sum = 789
mean = 39.45
variance = 888.448
standard deviation = 29.8068
How can I change the parameters?
I don't want to use this style.
template<class T, class Iter_T>
T computeVariance(Iter_T first, Iter_T last, T mean) {
return nthMoment<T, 2>(first, last, mean);
}
I want to use this way to calculate things.
template<class T, class T2>
T computeVariance(vector<T2> &vec, T mean)
{
...
}
All function should be like this. How can I do?
In main function how can I use generate function for copying vector and How can I send the addresses of the arguments
std::generate (v.begin(), v.end(), RandomNumber);
computeStats(v.begin( ), v.end( ), sum, mean, var, dev);

Answer 1

#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <functional>
#include <iostream>
#include <numeric>
#include <vector>
using namespace std;
template <int N, class T>
T nthPower(T x) {
T ret = x;
for (int i = 1; i < N; ++i) {
ret *= x;
}
return ret;
}
template <class T, int N>
struct SumDiffNthPower {
SumDiffNthPower(T x) : mean_(x){};
T operator()(T sum, T current) {
return sum + nthPower<N>(current - mean_);
}
T mean_;
};
template <class T, int N, class T2>
T nthMoment(vector<T2> &vec, T mean) {
size_t cnt = vec.size();
return accumulate(vec.begin(), vec.end(), T(), SumDiffNthPower<T, N>(mean)) / cnt;
}
template <class T, class T2>
T computeVariance(vector<T2> &vec, T mean) {
return nthMoment<T, 2>(vec, mean);
}
template <class T, class T2>
T computeStdDev(vector<T2> &vec, T mean) {
return sqrt(computeVariance(vec, mean));
}
template <class T, class T2>
void computeStats(vector<T2> &vec, T &sum, T &mean, T &var, T &std_dev) {
size_t cnt = vec.size();
sum = accumulate(vec.begin(), vec.end(), T());
mean = sum / cnt;
var = computeVariance(vec, mean);
std_dev = sqrt(var);
}
int RandomNumber() { return (std::rand() % 100); }
int main(int argc, char **argv) {
std::srand(unsigned(std::time(0)));
vector<int> v(20);
std::generate(v.begin(), v.end(), RandomNumber);
double sum, mean, var, dev;
computeStats(v, sum, mean, var, dev);
cout << "count = " << v.size() << "\n";
cout << "sum = " << sum << "\n";
cout << "mean = " << mean << "\n";
cout << "variance = " << var << "\n";
cout << "standard deviation = " << dev << "\n";
cout << endl;
return 0;
}
I hope this will work. PS: I didn't got your passing by argument thing. Explain it in comments, maybe I can help with you that.

Answer 2

you can have
template<class T, class T2>
T computeVariance(vector<T2> &vec, T mean)
{
return nthMoment<T, 2>(vec.begin(), vec.end(), mean);
}