Question

Hi I am trying to understand the following variable assignment in C, and try re-write it in R. I use R often but have only really glanced at C.

    int age,int b_AF,int b_ra,int b_renal,int b_treatedhyp,int b_type2,double bmi,int ethrisk,int fh_cvd,double rati,double sbp,int smoke_cat,int surv,double town
    )
    {
        double survivor[3] = {
            0,
            0.996994316577911,
            0.993941843509674

        };
    a = /*pre assigned*/ 
    double score = 100.0 * (1 - pow(survivor[surv], exp(a)) );
    return(score);
}

how does survivor[surv] work in this context? An explanation would be helpful, and any input on how to do the assignment in R would be a bonus.

Thanks very much!

Answer 1

This is an aggregate initializer:

double survivor[3] = {
    0,
    0.996994316577911,
    0.993941843509674
};

and is equivalent to:

double survivor[3];
survivor[0] = 0;
survivor[1] = 0.996994316577911;
survivor[2] = 0.993941843509674;

and survivor[surv] is the value stored at index of the survivor array. Array indexes run from 0 to N - 1 so if surv was 1 then survivor[surv] has value of 0.996994316577911.

---

Note, the function as currently written does not check that surv is a valid index for the array survivor (i.e. surv > -1 and surv < 3) and runs the risk of undefined behaviour.