Question

Create another program that inputs an integer from a user into a variable named: userInput

Check to see if the number is a prime number. If it is, the program should display:

xx is a Prime Number

-or-

xx is NOT a Prime Number

(where xx is the value in userInput

Answer 1

Hi,

Please find the below code in CPP with description:

#include <iostream>
using namespace std;

int main() {
    //Declare variables
    int i, userInput;
    
    //Declare boolean Variable
    bool isPrime = true;
    
    //Show Message tot end user and Get Input from user
    cout << "Enter a positive integer: ";
    cin >> userInput;

    // 0 and 1 are not prime numbers
    if (userInput == 0 || userInput == 1) {
        //Set boolean value to false if number are 0 or 1 entered by user without checking any calculations
        isPrime = false;
    }
    else {
        //Number for other than 0 or 1, we need to do calculations to check number is prime or NOT
        //loop start from 2
        //first try dividing it by 2, and see if you get a whole number
        for (i = 2; i <= userInput / 2; ++i) {
            if (userInput % i == 0) {
                //If you don't get a whole number, next try dividing it by prime numbers: 3, 5, 7, 11 
                //(9 is divisible by 3) and so on
                //if number is divisibly by 2 then its not a prime number
                isPrime = false;
                break;
            }
        }
    }
    
    //here check the boolena flag and accordinly print the message
    if (isPrime)
        cout << userInput << " is a prime number";
    else
        cout << userInput << " is NOT a prime number";

    return 0;
}

In the above example, 55 is divisible by 5 and 11 so 55 is NOT prime number

In case of 71, this number is not divisible by any number so 71 is prime number.

Thanks.