c语言运行出现 error C2065: 'printf' : undeclared identifier是什么意思？怎么改啊

Question

#define PI 3.14159
void main()
{
float r,h,l,s1,s2,v1,v2;
printf("20128082刘辉辉市场营销本科二班\n");
printf("请输入半径和高，格式为\n半径，高\n");
scanf("%f,%f",&r,&h);
l=2*PI*r;
s1=PI*r*r;
s2=4*PI*r*r;
v1=(4/3)*PI*r*r*r;
v2=s1*h;
printf("l=%.2f,s1=%.2f,s2=%.2f,v1=%.2f,v2=%.2f",l,s1,s2,v1,v2);
}

Answer 1

#include <stdio.h>