softmax function in c++

#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
#include <numeric>
 
double myfunction(double num) {
    return exp(num);
}
 
template <typename T>
void softmax(const typename::std::vector<T> &v, typename::std::vector<T> &s){
    double sum=0.0;
    transform(v.begin(), v.end(), s.begin(), myfunction);
    sum=accumulate(s.begin(), s.end(), sum);
    for(size_t i=; i<s.size(); ++i)
        s.at(i)/=sum;
}
 
int main() {
    double a[]={1.0, 3.0, 2.0};
    std::vector<double> v_a(a, a+sizeof a/sizeof a[]), v_b(v_a);
    std::vector<double>::const_iterator it=v_a.begin();
    for(; it!=v_a.end(); ++it) {
        std::cout<<*it<<" ";
    }
    std::cout<<std::endl;
    softmax(v_a, v_b);
    it=v_b.begin();
    for(; it!=v_b.end(); ++it) {
        std::cout<<*it<<" ";
    }
    std::cout<<std::endl;
    return ;
}