Не могу зациклить код на да/нет( - C (СИ)

#include "stdafx.h"
#include <conio.h>
#include <stdio.h>
#include <math.h>
#include <iostream>
 
using namespace std;
 
int main()
{
    char ext;
    do {
        char r = 0;
        int a = 0, b = 0, c = 0, D;
        double x1, x2;
        printf("a=");
        scanf_s("%d", &a);
        printf("\nb=");
        scanf_s("%d", &b);
        printf("\nc=");
        scanf_s("%d", &c);

        D = b*b - 4 * a * c;
        if (D < 0) printf("Korney net.");
        else {
            x1 = (-b - sqrt((double)D)) / 2 * a;
            x2 = (-b + sqrt((double)D)) / 2 * a;
            printf("x1=%f\nx2=%f\n", x1, x2);
        }
        printf("continue?(y/n)\n");
        scanf_s("%s", &ext);
        //if (r = 'y')ext = 1;
        //if (r = 'n')ext = 0;
        getchar();

    } while (ext == 'y');
 
    getchar();
    return 0;
}