C/C++ : Using both implementations of string in the same code : I would like to know whether the following code is "valid":

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<!-- language: lang-c++ -->

    #include <iostream>
    using namespace std;

    int main(void) {
        string s="Hello World!\n";
        for (int i=0;i<s.size();++i) {
            for (int j=0;j<s[i];++j) {
                cout << "+";
            }
            cout << ".>\n";
        }
    }

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I made this code but I don't know if I should add some ".c_str" or else, to make it better code.

Thanks in advance.

See you.