哎，这么简单的都搞不定

[valtti]

# include <stdio.h>
# include <conio.h>
# define PI 3.1415926
int main ()
{
printf ("本例要求用户输入圆的直径，计算圆的周长和面积\n");
printf ("请输入圆的直径并回车，退出请按n\n");
double zhi_jing ; //直径变量
do
{
scanf ("%lf",&zhi_jing);
double zhou_chang; //周长变量
double mian_ji; //面积变量
mian_ji = PI * (zhi_jing / 2)*(zhi_jing / 2); //计算公式

zhou_chang = PI * zhi_jing;
printf ("面积等于%lf,周长等于%lf\n",mian_ji,zhou_chang);



}while (不知道怎样写);
getch();
return 0;


}
//退不出while循环，如果用户输入的是int型的也不行，要加小数点，郁闷啊，c咋就这么弱智勒！！！！！！！不知道换成cin行不行

[龙哥依旧]

cin就C++了

[chengwenyao18]

# include <stdio.h>
# include <conio.h>
#include <iostream>
using namespace std;
# define PI 3.1415926
int main ()
{
	printf ("本例要求用户输入圆的直径，计算圆的周长和面积\n");
	printf ("请输入圆的直径并回车，退出请按n\n");
	char* zhi_jing1 = new char[10]; //直径变量
	char *str;
	do
	{
		//scanf ("%lf",&zhi_jing);
		cin>>zhi_jing1;
		if(0 == strcmp(zhi_jing1,"n"))
		{
			break;
		}
		double zhi_jing = atoi(zhi_jing1);
				
		double zhou_chang; //周长变量
		double mian_ji; //面积变量
		mian_ji = PI * (zhi_jing / 2)*(zhi_jing / 2); //计算公式

		zhou_chang = PI * zhi_jing;
		printf ("面积等于%lf,周长等于%lf\n",mian_ji,zhou_chang);

	}while (1);
	//getch();
	delete []zhi_jing1;
	zhi_jing1 = NULL;
	return 0;
}

[龙哥依旧]

# include <stdio.h>
# include <conio.h>
# define PI 3.1415926
int main ()
{
    printf ("本例要求用户输入圆的直径，计算圆的周长和面积\n");
    printf ("请输入圆的直径并回车，退出请按输入\"0\"\n");
    double zhi_jing ; //直径变量
    do
    {
        scanf ("%lf",&zhi_jing);
        double zhou_chang; //周长变量
        double mian_ji; //面积变量
        mian_ji = PI * (zhi_jing / 2)*(zhi_jing / 2); //计算公式
        
        zhou_chang = PI * zhi_jing;
        printf ("面积等于%lf,周长等于%lf\n",mian_ji,zhou_chang);
        
        
        
    }while ( zhi_jing == 0 );
    getch();
    return 0;
    
    
}