I've written an algorithm that has the following goal: finding all prime numbers up to a specified integer. I've made two different algorithms actually: on one hand, I've used the concept beyond the ancient sieve of eratosthenes; on the other, I've used a function called isprime() that tests if a number is prime. For instance, let's say I want to determine wich method is faster. So I need to time a piece of code in each algorithm.(adsbygoogle = window.adsbygoogle || []).push({});

As an example, here's the code of the first algorithm:

I've omitted the isprime() function definition, because I felt it's unnecessary. The problem with this approach is that my computer writes the numbers so rapidly that I probably will need to write the time in milliseconds if I wanted the algorithm to write every prime number up to a small number, as 11. Is there a function that allows me to do that?Code (Text):#include <stdio.h>

#include <math.h>

#include <time.h>

int isprime(int num);

int main () {

int n, num;

time_t t1, t2;

printf("Enter a number\n");

while (scanf("%d", &n) != 1) {

printf("Error: Try again.\n");

while (getchar() != '\n')

;

}

printf("Prime numbers\n");

time(&t1);

for (num = 2; num <= n; num += 1) {

if (isprime(num) == 1)

printf("%d\n", num);

}

time(&t2);

printf("Time elapsed: %f ms\n", (float)(t2-t1));

return 0;

}

Thank you on advance.

Links I've consulted

"[URL [Broken]

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# [C] time.h

**Physics Forums | Science Articles, Homework Help, Discussion**