计算常用圆形体体积
#define  PI  3.141592654
void cal ( int sel );
int main(void)
{   int sel;
    while( 1 ){
        printf("  1-计算球体体积\n");
        printf("  2-计算圆柱体积\n");
        printf("  3-计算圆锥体积\n");
        printf("  其他-退出程序运行\n");
        printf(“请输入计算命令：”);  
        scanf("%d",&sel);
        if (sel < 1 || sel > 3)
            break;         /*  输入非1~3，循环结束  */
        else
           cal (sel );    /*  输入1~3，调用cal()  */
    }
    return 0;
}
void cal ( int sel )
{   double  vol_ball(void );
    double  vol_cylind(void );
    double  vol_cone(void );
    switch (sel) {
           case 1:     printf("球体积为：%.2f\n", vol_ball( ));
            break;
        case 2:     printf("圆柱体积为：%.2f\n", vol_cylind( ) );
            break;
        case 3:     printf("圆锥体积为：%.2f\n", vol_cone( ) );
            break;
    }
}
double vol_cone( )
{   double r , h ;
    printf("请输入圆锥的底圆半径和高：");
    scanf("%lf%lf",&r,&h);
    return(PI*r*r*h/3.0);
}
double vol_cylind( )
{   double r , h ;
    printf("请输入圆柱的底圆半径和高：");
    scanf("%lf%lf",&r,&h);  
    return(PI*r*r*h);
}
double vol_ball( )
{    double r ;
     printf("请输入球的半径：");
     scanf("%lf",&r);
     return(4.0/3.0*PI*r*r*r);
}