編程求指定半徑r的圓的面值和周長，並輸出計算結果

#include <stdio.h>

void main( )

{

float circle_r = 0 , circle_mianji = 0, circle_zhouchang = 0 ;

printf("Please input a circle_r:\n" ) ;

scanf("%f", &circle_r ) ;

circle_mianji = PI * circle_r * circle_r ;

circle_zhouchang = 2 * PI * circle_ r ;

printf("circle_mianji is : %f\tcircle_zhouchang is : %f\n", circle_mianji, circle_zhouchang ) ;

}