为什么没办法循环-想要第二张图的效果

Question

#include <stdio.h>
#include <math.h>
int main()
{
double a, b, c, d, x1, x2;
char ch;
do
{
printf("请输入一元二次方程的三个系数：\n");

    printf("请输入系数 a = \t");
    scanf_s("%lf", &a);

    printf("请输入系数 b = \t");
    scanf_s("%lf", &b);

    printf("请输入系数 c = \t");
    scanf_s("%lf", &c);

    if (a != 0)
    {
        d = b * b - 4 * a * c;//根的判别式

        if (d > 0)
        {
            x1 = (-b + sqrt(d)) / (2 * a);
            x2 = (-b - sqrt(d)) / (2 * a);
            printf("有2个实数根：x1 = %.2lf  x2 = %.2lf\n", x1, x2);
        }
        else if (d == 0)
        {
            x1 = (-b + sqrt(d)) / (2 * a);
            printf("有2个相等实数根：x1=x2 = %.2lf\n", x1);
        }
        else
            printf("无实数根\n");
    }
    else
    {
        x1 = (-c) / b;
        printf("有一个实数根：x1=%.2lf\n", x1);
    }
        printf("是否继续吗：Y/N\n");
        scanf_s("%c", &ch);
} while (ch == 'y' || ch == 'Y');
return 0;

}

Answer 1

需要添加getchar() ，接收一下前面的换行符， 修改如下：

#include <stdio.h>
#include <math.h>
int main()
{
    double a, b, c, d, x1, x2;
    char ch;
    do
    {
    printf("请输入一元二次方程的三个系数：\n");

    printf("请输入系数 a = \t");
    scanf_s("%lf", &a);
 
    printf("请输入系数 b = \t");
    scanf_s("%lf", &b);
 
    printf("请输入系数 c = \t");
    scanf_s("%lf", &c);
 
    if (a != 0)
    {
        d = b * b - 4 * a * c;//根的判别式
 
        if (d > 0)
        {
            x1 = (-b + sqrt(d)) / (2 * a);
            x2 = (-b - sqrt(d)) / (2 * a);
            printf("有2个实数根：x1 = %.2lf  x2 = %.2lf\n", x1, x2);
        }
        else if (d == 0)
        {
            x1 = (-b + sqrt(d)) / (2 * a);
            printf("有2个相等实数根：x1=x2 = %.2lf\n", x1);
        }
        else
            printf("无实数根\n");
    }
    else
    {
        x1 = (-c) / b;
        printf("有一个实数根：x1=%.2lf\n", x1);
    }
    getchar(); // 接收一下前面的换行
    printf("是否继续吗：Y/N\n");
    scanf_s("%c", &ch);
    } while (ch == 'y' || ch == 'Y');
    return 0;
}