Combining a vector of strings

Assuming this is question 6.8, it doesn't say you have to use accumulate - it says use "a library algorithm". However, you can use accumulate:

#include <numeric>

int main () {
    std::string str = "Hello World!";
    std::vector<std::string> vec(10,str);
    std::string a = std::accumulate(vec.begin(), vec.end(), std::string(""));
    std::cout << a << std::endl;
}

All that accumulate does is set 'sum' to the third parameter, and then for all of the values 'val' from first parameter to second parameter, do:

sum = sum + val

it then returns 'sum'. Despite the fact that accumulate is declared in <numeric> it will work for anything that implements operator+()