c语言求圆的面积和周长

Question

#define n 3.1415926
#include<stdio.h>
void main()
{
double s,l,r;
scanf("%f",&r);
s=n*r*r;
l=2*n*r;
printf("s=%f\n l=%f\n",s,l);
}
输出答案不正确，将double换成float答案正确，但精度变小

Answer 1

C#程序：

using System;

class Program

{

    static void Main()

    {

        double r;                                 //圆半径

    double circle;                           //圆周长

    double area;                            //圆面积

    const double PI = 3.14159;      //π

        Console.Write("请输入半径：");

        r = double.Parse(Console.ReadLine());

        circle = 2 * PI * r;        //计算圆周长

    area = PI * r * r;          //计算圆面积

    Console.WriteLine("半径为{0}的圆周长为{1}", r, circle);

        Console.WriteLine("半径为{0}的圆周长为{1}", r, area);

    }

}

运行测试：

Answer 2

#define n 3.1415926
#include<stdio.h>
void main()
{
double s,l,r;
scanf("%lf",&r);
s=n*r*r;
l=2*n*r;
printf("s=%lf\n l=%lf\n",s,l);  //float 对应%f  double对应 %lf
}

Answer 3

#include<stdio.h>
#define IP 3.1416
main()
{
float r,l,s;
printf("please enter a number\n");
scanf("%f",&r);
l=2*IP*r;
s=IP*r*r;
printf("l=%f\ns=%f\n",l,s);
}