Functional programming in C

fp.c

#include <stdio.h>

double sum(const double *x, double s, size_t n)
{
    if (n == 0)
    {
        return s;
    }

    return sum(x + 1, s + *x, n - 1);
}

double mean(const double *x, size_t n)
{
    double s = sum(x, 0.0, n);
    double m = s / n;
    return m;
}

int main(int argc, char **argv)
{
    size_t n = 5;
    double x[] = {1, 2, 3, 4, 5};
    double m = mean(x, n);
    printf("m = %f\n", m);
    return 0;
}