代码

#include <cstdio>
#include <cmath>
using namespace std;

double sqrt(double x);

int main() {
	double x = 1000;
	printf("%.3lf\n", sqrt(x));
	return 0;
}

double sqrt(double x) {
	double l = 1, r = x, mid;

	for (mid = (l + r) / 2; abs(mid * mid - x) > 1E-5; mid = (l + r) / 2)
		if (mid * mid < x)
			l = mid;
		else
			r = mid;

	return mid;
}

评测结果