Thread: Alternative way for void type help!

Alright have finally done it. And this is my code. See if there is anything that could be truncated or left off. I appreciate it. And thanks Cornedbee for clarifying the question.

Code:

#include <iostream>
#include <math.h>
using namespace std;

// Function must be declared before being used.
int prime(int n);

int main(){
         int i;

// Set up an infinite loop; break if user enters 0.
// Otherwise, evaluate n from prime-ness.
while(1){
         cout << "Enter a number (0 to exit)";
         cout << "and press ENTER: ";
         cin >> i;
         if(i == 0)
              break;
         for(i = 2; i <= 22; i++)                      // Test all numbers from 2 to 22
         if(prime(i)){                                 // state for each mumber whether it is a prime
                 cout<< i << "is prime" << endl;       // and print out all numbers.
         }else{
                 cout<< i << "is not a prime" << endl;
         }
}
          return 0;
}

// Prime number function. Test divisors from
// 2 to sqrt of n. Return false if a divisor
// found; otherwise, return true.
int prime(int n){
         int i;
         for(i = 2; i <= sqrt((double) n); i++)
                      if(n % i == 0)
                            return false;         // n is not prime.

          return true;    // If no divisor found, n is prime.
}

So would you give me some hints on how to optimize it? I am at a loss as it is a bit confusing to me when it comes to computing the square root before the loop and the iteration.

So make another variable, like

Code:

double bob = sqrt(n);

and then use bob in your for-loop test.

I don't understand any of what you're asking. What I said was to do this:

Code:

double bob = sqrt(n);
for (int i = 2; i <= bob; i++) {
    //the rest of your prime testing
}

Apart from that, yes you should get rid of the cout/cin at the beginning of your program, since as you say you are not accepting any input from the user.