好奇怪，sacnf（）出现问题

今天看《c语言入门经典》，照例打打代码练练手.

打了一段算术运算，居然无法运行。

代码如下。问题出现在“scanf（）”那一行：

//program 2.8 calculations on a table

include

int main(void){
float radius = 0.0f;//the raidus of the table
float diameter = 0.0f;//the diameter of the table
float circumference = 0.0f;//the circumference of the table
float area = 0.0f;//the area of the table
float pi = 3.14159265f;

printf("input the diameter of the table:");
scanf("%f", &diameter);//read the diameter from the keyboard

radius = diameter / 2.0f;//calculate the radius
circumference = 2.0f*pi*radius;//calculate the circumference
area = pi*radius*radius;//calculate the area

printf("\nthe circumference is %.2f", circumference);
printf("\nthe area is %.2f\n", area);
return 0;

}
————————————————————————————————————
20170320有新发现：
//program 3.1 a simple example of the if statement

include

int main(){
int number = 0;
printf("\nenter an integer between 1 and 10: ");
scanf_s("%d", &number);

if (number > 5 )
    printf("you entered %d which is greater than 5 \n", number);
if (number < 6)
    printf("you entered %d which is less than 6 \n", number);
return 0;

}

问题的关键是把“ scanf ”改为“ scanf_s ”，IDE给出的原因是 scanf unsafe 。

具体为什么，有待解决。