ProgrammingThis forum is for all programming questions.
The question does not have to be directly related to Linux and any language is fair game.
Notices
Welcome to LinuxQuestions.org, a friendly and active Linux Community.
You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. Registration is quick, simple and absolutely free. Join our community today!
Note that registered members see fewer ads, and ContentLink is completely disabled once you log in.
If you have any problems with the registration process or your account login, please contact us. If you need to reset your password, click here.
Having a problem logging in? Please visit this page to clear all LQ-related cookies.
Get a virtual cloud desktop with the Linux distro that you want in less than five minutes with Shells! With over 10 pre-installed distros to choose from, the worry-free installation life is here! Whether you are a digital nomad or just looking for flexibility, Shells can put your Linux machine on the device that you want to use.
Exclusive for LQ members, get up to 45% off per month. Click here for more info.
hey, i have been reading these forums for a while but just signed for an account. any how, here is my problem, i'm kind of new to c++, i'd i thought i'd dabble a little to get use to it. i'm writing a program to specify prime numbers in a given range, but i don't believe it is runnig my functions, or that it is not going through the loops, here is my code
#include <iostream>
using namespace std;
unsigned long a , b;
int prime(unsigned long number);
int lookforprime(unsigned long lowerNumber, unsigned long upperNumber);
int main(){
cout << "This program will determine if there are any prime numbers" << endl;
cout << "in a range that you specify." << endl;
cout << "Enter the lower limit: ";
cin >> a;
cout << "Enter the upper limit: ";
cin >> b;
lookforprime(a , b);
cout << "Thanks, Come Again." << endl;
return 0;}
int lookforprime(unsigned long lowerNumber , unsigned long upperNumber){
for( unsigned long i = lowerNumber ; i == upperNumber ; i++){
prime(i);
cout << "program is running" << endl;}
return 0;}
int prime(unsigned long number){
for(unsigned long divisor = --number ; divisor == 1 ; divisor--){
if((number % divisor) == 0){
cout << number << " is not prime";
return 0;}
cout << number << " is prime" << endl;
return 0;
}}
thanks to both of you the loop does work, i've been out of programming so long, i just need to get use to it again. Brane Ded can you tell me why it won't work without telling me how to make it work?
It will not work because the devisor >= 1, the loop will execute for
devisor > 1 and also for devisor == 1.
So as each number is divisible by 1 and (any_number % 1 ) is always 0.
So ...............
Thought of using Fermat's Little Theorem instead of a brute force search to test for primality? Also, you don't need to start at (number-1), but at sqrt(number).
LinuxQuestions.org is looking for people interested in writing
Editorials, Articles, Reviews, and more. If you'd like to contribute
content, let us know.