Editing Higher-order function (section)

====Function pointers====
[[Function pointer]]s in languages such as [[C (programming language)|C]], [[C++]], [[Fortran]], and [[Pascal (programming language)|Pascal]] allow programmers to pass around references to functions. The following C code computes an approximation of the integral of an arbitrary function:

<syntaxhighlight lang="c">
#include <stdio.h>

double square(double x)
{
    return x * x;
}

double cube(double x)
{
    return x * x * x;
}

/* Compute the integral of f() within the interval [a,b] */
double integral(double f(double x), double a, double b, int n)
{
    int i;
    double sum = 0;
    double dt = (b - a) / n;
    for (i = 0;  i < n;  ++i) {
        sum += f(a + (i + 0.5) * dt);
    }
    return sum * dt;
}

int main()
{
    printf("%g\n", integral(square, 0, 1, 100));
    printf("%g\n", integral(cube, 0, 1, 100));
    return 0;
}
</syntaxhighlight>

The [[qsort]] function from the C standard library uses a function pointer to emulate the behavior of a higher-order function.