C++: A question of efficiency.

[ItecKid]

Hello,

I am writing a C++ program to find the largest such number such that the square root of that number is less than or equal to a fixed number, set by me, like this:

#include <stdio.h>
#include <math.h>
int main (void)
{
        long fixed, param, result;
        result = 0;
        param = 1;
        fixed = 20;
        while (result < fixed) {
                result = sqrt(param);
                param++;
        }
        param -= 1;
        printf ("%d\n", param);
        return 0;
}

This works fine as is, but the trouble is that my fixed is a number between 10^6 and 3 * 10^15, so this code is not optimal for computing values on such large scale. What can be done to increase efficiency?

Thank you.

[VernonDozier]

Hello,

I am writing a C++ program to find the largest such number such that the square root of that number is less than or equal to a fixed number, set by me, like this:

#include <stdio.h>
#include <math.h>
int main (void)
{
        long fixed, param, result;
        result = 0;
        param = 1;
        fixed = 20;
        while (result < fixed) {
                result = sqrt(param);
                param++;
        }
        param -= 1;
        printf ("%d\n", param);
        return 0;
}

This works fine as is, but the trouble is that my fixed is a number between 10^6 and 3 * 10^15, so this code is not optimal for computing values on such large scale. What can be done to increase efficiency?

Thank you.

Why bother taking a square root? Why not just square the fixed number?:

int fixed = 20;
int largest = fixed * fixed;  // 400

[ItecKid]

I had to stare at your reply for several minutes before realizing that that is a much better, faster way to solve my problem...thank you.