C++ for Beginners: C++ Program to Display Prime Numbers Between Two Intervals

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(C++ programming Example for Beginners)

C++ Program to Display Prime Numbers Between Two Intervals

Example to print all prime numbers between two numbers (entered by the user) in C++ Programming. This problem is solved using nested for loop and if…else statement.

 


Example #1: Display Prime Numbers Between two Intervals


#include <iostream>
using namespace std;

int main(){
    int low, high, i, flag;

    cout << "Enter two numbers(intervals): ";
    cin >> low >> high;

    cout << "Prime numbers between " << low << " and " << high << " are: ";

    while (low < high)
    {
        flag = 0;

        for(i = 2; i <= low/2; ++i)
        {
            if(low % i == 0)
            {
                flag = 1;
                break;
            }
        }

        if (flag == 0)
            cout << low << " ";

        ++low;
    }

    return 0;
}

Output

Enter two numbers(intervals): 20 50 Prime numbers between 20 and 50 are: 23 29 31 37 41 43 47

In this program, the while loop is iterated (high - low - 1) times.

In each iteration, whether low is a prime number or not is checked and the value of low is incremented by 1 until low is equal to high.


Example #2: Display Prime Numbers When Larger Number is Entered first


#include <iostream>
using namespace std;

int main(){
    int low, high, flag, temp;
    
    cout << "Enter two numbers(intevals): ";
    cin >> low >> high;

    //swapping numbers if low is greater than high
    if (low > high) {
        temp = low;
        low = high;
        high = temp;
    }
    cout << "Prime numbers between " << low << " and " << high << " are: ";

    while (low < high)
    {
        flag = 0;

        for(int i = 2; i <= low/2; ++i)
        {
            if(low % i == 0)
            {
                flag = 1;
                break;
            }
        }
        if (flag == 0)
            cout << low << " ";

        ++low;
    }
    return 0;
}

 

 

C++ for Beginners: C++ Program to Display Prime Numbers Between Two Intervals

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