Question

My C++ code won't loop like it should. What am I doing wrong?

#include <iostream>
using namespace std;

int main()
{
   int n;
   int flag= 1;
   cout << "Prime/Not Prime" << endl;
   cout << "Enter the Number to check Prime:" << endl;
   cin >> n;
   int m = n / 2;
   int i;
   for (i = 2; i <= m; i++)
       if (n % i == 0)
           flag = 0;
   if (flag == 0)
       cout << "Number is not Prime " << endl;
   else
       cout << "Number is Prime" << endl;
}

Answer 1

Screenshot

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Program

//Header file
#include <iostream>
using namespace std;
int main()
{
   //Variable for input read
   int n;
   //Variable to check prime or not
   int flag = 1;
   //Header
   cout << "Prime/Not Prime" << endl;
   //Prompt for input
   cout << "Enter the Number to check Prime:";
   cin >> n;
   //Get half of the number
   int m = n / 2;
   //Loop to find prime or not
    //If it divisible by any number , then not prime
   for (int i = 2; i <= m; i++) {
       if (n % i == 0) {
           flag = 0;
       }
          
   }
   //Check and display  
   if (flag == 0)
       cout << "Number is not Prime " << endl;
   else
       cout << "Number is Prime" << endl;
}

-------------------------------------

Output

Prime/Not Prime
Enter the Number to check Prime:121
Number is not Prime

-------------------------------------------------------

Note

This program is working perfectly, what actually you expect,.

Is it repeated to enter input?

I assume you want that way then check the below code.

Program

//Header file
#include <iostream>
using namespace std;
int main()
{
   //Variable for input read
   int n;
   while (true) {
       //Variable to check prime or not
       int flag = 1;
       //Header
       cout << "Prime/Not Prime" << endl;
       //Prompt for input
       cout << "Enter the Number to check Prime:";
       cin >> n;
       //Get half of the number
       int m = n / 2;
       //Loop to find prime or not
       //If it divisible by any number , then not prime
       for (int i = 2; i <= m; i++) {
           if (n % i == 0) {
               flag = 0;
           }

       }
       //Check and display  
       if (flag == 0)
           cout << "Number is not Prime " << endl;
       else
           cout << "Number is Prime" << endl;
       //Repeatation part
       char ch;
       cout << "Do you want to enter next number(y/n)? ";
       cin >> ch;
       ch = toupper(ch);
       //Error check
       while (ch != 'Y' and ch != 'N') {
           cout << "ERROR!!!Choice should be y/n." << endl;
           cout << "Do you want to enter next number(y/n)? ";
           cin >> ch;
           ch = toupper(ch);
       }
       //exit from program
       if (ch == 'N'){
           exit(0);
       }
   }
}