想问问为什么我的输出结果都是0

Question

#include <stdio.h>
int main(){
double r;
double girth;
girth= 2.0 * 3.14 * r ;
double area;
area= 3.14 * r * r;
scanf("%f",&r);
printf("圆形的周长是%f",girth);
printf("圆形的面积是%f",area);
return 0;｝

Answer 1

girth没初始化，默认为0