Prime Numbers Between 1-1000

Monday, September 09, 2013 Vinster 5 Comments A⁺ a^-

C++ program to find prime numbers between 1 to 1000

Problem:

Write a C++ program which prints all the prime numbers from 1-1000.

Prime numbers are numbers greater than 1 and which has 1 and the number itself as positive factors or divisors. It doesn't have a positive factor or divisors other than 1 and the number itself.

Let's take 5 for example:
1 and 5 (the number itself) can evenly divide 5 so they are factors of 5.
2, 3, 4 are cannot evenly divide 5 so they are not factors of 5.
Therefore, 5 is a Prime Number.

This is a program which shows the Prime Numbers from 1-1000.

/*
Prime Numbers (from 1 - 1000)
*/
#include <iostream>

using namespace std;

int main(void)
{
 int num,i,countFactors;
 char hang;

 cout << "Prime numbers (1-1000) : " << endl;

 for (num = 1; num <= 1000; num++)
 {
  countFactors = 0;

  for (i = 2; i <= num; i++)
  {
   //if a factor exists from 2 up to the number, count Factors
   if (num % i == 0)
   {
    countFactors++;    
   }
  }

  //a prime number has only itself as a factor
  if (countFactors == 1)
  {
   cout << num << ", ";
  }
 }

 //to let console stay
 cin >> hang;

 return 0;
}