Question

//Testing numbers for primality

#include <iostream>
#include <cmath>
using namespace std;

int main() {

int n;          //User input number
int i;          //Input number will be divided by i
int count;      

count = 0;

cout << endl;   

while(n != 'q') {

    cout << "#: ";
    cin >> n;       

    for(i = 1; i <= n; i++) {   
                    //increase the divisor until it's equal to n                
        if(n % i == 0) {
             count++;
        }       
        //If there is no remainder, count increases by 1. Since prime numbers are only divisible by 1 and themselves, count will be exactly 2 in the case of a prime number.

    }

    if(count == 2) {
        cout << "   1\n";       //1 = yes prime

    }else if(count != 2) {      
        cout << "   0\n";       //0 = not prime

    }

    count = 0;

}

if(n == 'q') {
    return(0);
}
}

Here I am testing numbers to see if they are prime. Count increases every time the remainder of division n/i is 0 so when count=2, output is 1 for yes, otherwise 0 for no. I’ve gotten the program to test as many numbers as I want correctly during a session, but I am trying to create an escape sequence.

I tried using the condition (n==’q’) for quit, but when I input q, the program loops infinitely. I tried putting a break; statement for this condition within the while loop but the result is the same. I am guessing this problem has to do with char-int/int-char conversion. Can someone hint to me how I can create a working exit sequence?

Answer 1

You have no code that can read a q. Your input logic only accepts a number. You then test if that number is equivalent to a q character. The equivalent integer to the letter q is 113. If you try that, it will quit.

Since you really want to input a number or a letter, you’ll need to write input logic that can accept either. Then you’ll need to check what input you got, and then process it accordingly.