将函数e ^（ - x）和e ^（ - x ^ 2）传递给C中的计算函数

Question

I have to write a program that passes the functions e^(-x) and e^(-x^2) into another function, called calculateIntegral() , which will then calculate the integral of the function.

Restrictions:

• calculateIntegral() is the function which will be used to compute the integral of both e^(-x) and e^(-x^2)
• I can only have the function passed, the a and b bounds, and the number of intervals as the arguments for function calculateIntegral() .

I've thought about changing x to, say, -x outside the function and assigning it to another variable to compute in e^(x) , but then I would have to include that as another argument in calculateIntegral() .

Is there any way to alter the original e^(x) , so that when it gets passed into calculateIntegral() , it would be e^(-x) so the rest function would just have to plug the bounds into that equation for calculations?

Answer 1

What you want is to parametrize the integrand, so you want to be able to pass the function that f has to integrate as a parameter. In C, this can be done with function pointers :

// IntegrandT now is the type of a pointer to a function taking a double and
// returning a double
typedef double (*IntegrandT)(double);

// The integration function takes the bound and the integrand function
double f(double min, double max, IntegrandT integrand)
{
    // here integrand will be called as if it were a "normal" function
}

// Your example functions
double minusExp(double x)
{
    return exp(-x);
}

double unitaryGaussian(double x)
{
    return exp(-x*x);
}

// now you can do
double res=f(-10, 10, minusExp);
double res2=f(-10, 10, unitaryGaussian);

For more details about function pointers, check your C manual.