Do it again: do-while loop
The repeat loop in R is called a do while loop in C++. Compared to a while loop, it moves the condition to the end of the loop, so that the loop contents are guaranteed to be run at least once. The syntax is as follows:
do {
// Do something
} while(condition);
Notice the semicolon after the while condition.
This exercise is part of the course
Optimizing R Code with Rcpp
Exercise instructions
- Initiate the loop with a
dostatement. - Specify the
whilecondition, so the loop keeps iterating while the value ofis_good_enoughis false.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
#include
using namespace Rcpp;
// [[Rcpp::export]]
double sqrt_approx(double value, double threshold) {
double x = 1.0;
double previous = x;
bool is_good_enough = false;
// Initiate do while loop
___ {
previous = x;
x = (x + value / x) / 2.0;
is_good_enough = fabs(x - previous) < threshold;
// Specify while condition
} ___
return x;
}
/*** R
sqrt_approx(2, 0.00001)
*/