#include <stdio.h>
#define PI 3.1415926;
void main(void)
{
double  a=3.0;
double  b=PI*a*a;
printf("\na=%f",a);
}
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : error C2100: illegal indirection
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : warning C4552: '*' : operator has no effect; expected operator with side-effect
执行 cl.exe 时出错.

#include <stdio.h>
#define PI 3.1415926
void main(void)
{
float  f radius = 3.0;
float  f area = PI*f radius*f raduis;
printf("\n area=%f",area);
}
怎么回事我试了好多次还是有问题，求前辈指教，新手上路
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(5) : error C2146: syntax error : missing ';' before identifier 'radius'
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(5) : error C2065: 'radius' : undeclared identifier
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(5) : warning C4244: '=' : conversion from 'const double' to 'int', possible loss of data
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : error C2146: syntax error : missing ';' before identifier 'area'
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : error C2086: 'f' : redefinition
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : error C2065: 'area' : undeclared identifier
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : warning C4244: '=' : conversion from 'double' to 'int', possible loss of data
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : error C2146: syntax error : missing ';' before identifier 'radius'
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : error C2146: syntax error : missing ';' before identifier 'raduis'
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : warning C4552: '*' : operator has no effect; expected operator with side-effect
E:\游戏\Microsoft Visual Studio\MyProjects\w\x.cpp(6) : error C2065: 'raduis' : undeclared identifier
执行 cl.exe 时出错.
求前辈赐教，谢谢

double  b=PI*a*a;
改成double  b=a*a*PI;试试
还有printf("\na=%f",a);打印的是a，你应该是想要打印b的值吧

第一个程序#define PI 3.1415926;中多了一个分号
改为#define PI 3.1415926