用函数来计算圆，正方形和长方形

#include
#include
void calcs();//计算圆的面积
void calcnum();//计算正方形的面积
void calcsum();//长方形面积的计算
int main()
{
    int choice;
    while(1)
   {
    printf("<<<<<<<常见的图形面积计算>>>>>>>\n");
    printf("1,圆\n");
    printf("2,正方形\n");
    printf("3,长方形\n");
    system("color 8E");
    scanf("%d",&choice);
    switch(choice)
    {
    case 1:
        calcs();


        break;
    case 2:
        calcnum();
        break;
    case 3:
        calcsum();
        break;
    }
   }


}
void calcsum()
{
    double length,wide,s;//长，宽,面积
     system("color F2");
    printf("请输入长，宽:");
    scanf("%lf %lf",&length,&wide);
    s = length * wide;
    printf("面积为：%.2lf\n",s);

}
void calcnum()
{
    double length;
    double s;
     system("color E4");
    printf("请输入边长：");
    scanf("%lf",&length);
    s = length * length;
   printf("面积为：%.2lf\n",s);
}
void calcs()
{
    double radius,s;
     system("color 74");
    printf("请输入半径：");
    scanf("%lf",&radius);

    s = radius * radius * 3.14;
     printf("面积为：%.2lf\n",s);
}