C语言中的while循环输入

Question

我正在尝试学习C语言，并编写了一个计算各种形状面积的小程序。以下是源代码：

#include "stdafx.h"

struct entry
{
    float x;
    float y;
};

void square()
{
    printf("\nPlease enter the size of one of the square's sides\n");

    struct entry sq;
    scanf_s("%f\n", &sq.x);

    printf("\nThe area of the square is %.2f\n\n", sq.x * sq.x);
}

void rectangle()
{
    printf("\nPlease enter the length and breadth of the rectangle\n");

    struct entry rec;
    scanf_s("%f\n", &rec.x);
    scanf_s("%f\n", &rec.y);

    printf("\nThe area of the rectangle is %.2f\n\n", rec.x * rec.y);
}

void triangle()
{
    printf("\nPlease enter the width and height of the triangle\n");

    struct entry tri;
    scanf_s("Width: %f\n", &tri.x);
    scanf_s("Height: %f\n", &tri.y);

    printf("\nThe area of the triangle is %.2f\n\n", (tri.x * tri.y)/2);
}

void circle()
{
    printf("\nPlease enter the radius of the circle\n");

    struct entry circ;
    scanf_s("%f\n", &circ.x);

    printf("\nThe area of the circle is %.2f\n\n", 3.14 * circ.x * circ.x);
}


void main()
{
    int input = 0;

    do
    {
        printf("---Area of a Shape---\n\n");
        printf("1. Square\n");
        printf("2. Rectangle\n");
        printf("3. Triangle\n");
        printf("4. Circle\n");
        printf("5. Exit\n");
        printf("\n\n");

        printf("Please make a choice\n");
        scanf_s("%d", &input);

        switch(input)
        {
            case 1: square();
                    break;

            case 2: rectangle();
                    break;

            case 3: triangle();
                    break;

            case 4: circle();
                    break;

            case 5: printf("\n\nThank you for using this program!  Press enter to exit!\n");
                    break;

            default: printf("\nInvalid choice!\n\n");
                    break;
        }       
    }
    while(input != 5);

    getchar();
    getchar();
}

我对这个程序唯一的问题是，在输入边长以计算面积后，它会等待我再次输入另一个数字（进行选择）才显示答案。我不知道问题出在哪里。我认为在移动到另一个函数之前，C会确保执行完整个函数。您能否帮助我解决这个问题？谢谢。

- Matthew

Answer 1

在您的scanf格式中，

scanf_s("%f\n", &rec.x);

'\n' 不代表一个字面上的 '\n'，而是任意的空格字符序列。因此，在输入数字（和空格）之后，scanf_s 调用不会结束，直到您输入一个非空格字符（在此之后可能将输入发送到程序）。只需从格式中删除 '\n'。

- Daniel Fischer