Iterator and tolower problem

[Iceboxes]

(Noob question)
I am trying to write a function that takes a string and converts every character to lowercase. Problem is, it doesnt...

I am able to compile the program and run it, but the program doesnt turn the string I input into lowercase.

Here is the function:

void toLow(string &s){
    for (auto i = s.begin(); i != s.end(); i++)
    {
        tolower(*i);


    }
}

I have tried using a temporary char to be a middleman in the conversion (I am basically trying anything on the top of my head, because I dont understand the problem, or atleast, I cant see it..) but, without luck.

I dont NEED an example, just someone to point out the error in the code and a point in the right direction. It is probably just a derp error... (I have a lot of them)

[DeadPlanet]

*i = tolower(*i)?

[Iceboxes]

AS I SAID... derp error.. omg >.< #fml

[Elysia]

void ToLow(string& s)
{
    for (auto & c : s)
        c = tolower(c);
}

...or...

void ToLow(string& s)
{
    std::transform(s.begin(), s.end(), s.begin(), &tolower);
}