C++ program to display prime numbers between two intervals

In this example, you will learn about C++ program to display prime numbers between two intervals.

This program also checks for the higher number and performs swapping if the first number is greater than the second.

A number is called prime number if it is divisible by 1 and itself only.

For example: 1, 3, 5, …., 91, ….

Example: C++ program to display prime numbers between two intervals

#include <iostream>
using namespace std;

int main ()
{
   int num1, num2, i, j, temp, flag;

   cout << "Enter two numbers(intervals): " << endl;
   cin >> num1 >> num2;

   //swapping numbers if first number is greater than second one
   if (num1 > num2)
   {
      temp = num1;
      num1 = num2;
      num2 = temp;
   }

   cout << "\nPrime numbers between " << num1 << " and " << num2 << " are:" << endl;
   // Displaying prime number between num1 and num2
   for (i = num1 + 1; i < num2; ++i)
   {
      flag = 0; //flag is set to 0
      for (j = 2; j <= i/2; ++j)
      {
         if (i % j == 0)
         {
            flag = 1;
            break;
         }
      }
      if (flag == 0) //if flag == 0, then display i
         cout << i << "\t";
   }
   cout << "\n\n";
   return 0;
}

Output

Explanation

This program will works if the first number is greater than the second one because if condition checks and performs swapping if necessary.

First for loop will continue till the first number equals the second.

flag will set to 1 if the number is perfectly divisible by other numbers than 1 and itself and break operation will occur.