Question

You cin a value to the variable f. f could be something like:

pow(5.957,-X*X*X*X)-cos(X*X) +20*sin(X*X)

or some other complicated math function. I also tried to declare it directly as such.

f = pow(5.957,-X*X*X*X)-cos(X*X) +20*sin(X*X);
std::cout << "Bisection method on function,  f = " << f << " "<<std::endl;

The output is on both MinGW and VS2010:

f = nan

How do I get cout to print f on the screen?

I declared f as such

double F(double X) { double f; f =  pow(5.957,-X*X*X*X)-cos(X*X) +20*sin(X*X); return f; }

I’m basically writing a C++ program to perform different numerical methods for finding roots on the function: bisection, Monte Carlo, Newtwon’s method etc. Those work, but I want to display the function to the user after he types it in, and it just shows up as NaN.

Answer 1

From the looks of it, you are trying to define f as an actual mathematics function (in the direct way of doing it). That definitely won’t work.

But if you have a string, then f will output a string, ignoring the mathematics function.

Remember, unlike other programming languages, C++ is very…temperamental.

You can’t assign a character to an int and vice versa. But string can hold anything because it is only a piece of text.

Try using getline…just wait a sec and I’ll go get my book..

Edit: Okay. If you use getline (cin, foo);, where foo is defined as string foo and you include <string>, this should work. Is that what your coding originally looked like?

Edit2: You should still be able to use stream to convert from a string back and forth…but I’d need somebody more experienced than me to confirm that.