Loop over an array in C++ [duplicate]

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• What is a C++11 extension [-Wc++11-extensions] 1 answer

I am trying to handle C++ through examples of Numerical Analysis (root finding using different methods)

For this purpose, I would like to loop over an array of initial values and try several methods for each value. I found one way to loop on another topic, but it doesn't totally solve my problem :

int main(int argc, char **argv) {
    double init[] = {-2, 3.8, 20, -40};
    int N = 5;
    for(const double &x : init)
        cout << "value of x" << FindRootNewton(x,N) << endl;
        cout << "value of x" << FindRootSecant(x,N) << endl;
    return 0;
}

I have 2 problems with this code :

1. I have a warning on the line starting the loop (for ...) : range-based for loop is a C++11 extension [-Wc++11-extensions] What does it mean ? I think I have a C++98 compiler, I tried to figure out using __cplusplus macro and the output is 199711L.

2. He can't read the second line of the loop, "use of undeclared identifier x", as if the variable vanished after first use.. But if I comment this second line out, all works fine.

Thanks for any help on this