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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).

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