c++上机实验

6. 编程输出如下图形：
*
          *****
*********
*************
    *****************
  *********************

/*

title:3-6
input: n lines
output: 金字塔*
*/
#include <iostream>
using namespace std;
void main()
{
	int n;//n lines
	int mid,count;
	int i,j;
	cout<<"please input n:"<<endl;
	cin>>n;
	mid = (n-1)*2 + 1;
	count = mid * 2 -1;
	i = 0;
	while (i < n)
	{
		for (j=1;j<=count;j++)
		{
			if(j < mid-2*i || j > mid+2*i)
				cout<<" ";
			else cout<<"*";
			
		}
		cout<<endl;
		i++;	
	}
}

评论

4 楼 vanillalyx 2009-06-08  

2. 参照以下代码，定义一个车(vehicle)基类，有Run、Stop等成员函数，由此派生出自行车(bicycle)类、汽车(motorcar)类。从bicycle和motorcar派生出摩托车(motorcycle)类，它们都有Run、Stop等成员函数。观察虚函数的作用。

#include <iostream.h>

class Vehicle
{
private:
	int maxSpeed;
	int weight;
public:
	Vehicle()
	{
		maxSpeed = 0;
		weight = 0;
	}
	~Vehicle() {}
	virtual	 void run() {cout << "A Vehicle is running!" << endl;}
	virtual void stop() {cout << "A Vehicle has stopped!" << endl;}
	////观察加上virtual和去掉virtual后程序的区别
};

class Bicycle : virtual public Vehicle // //多重继承时均采用了虚基类的方法，避免二义性
{
private:
	int no;
public:
	Bicycle() {}
	~Bicycle() {}
	void run() {cout << "A Bicycle is running!" << endl;}
	void stop() {cout << "A Bicycle has stopped!" << endl;}
};

class MotorCar : virtual public Vehicle
{
private:
	int size;
public:
	MotorCar() {}
	~MotorCar() {}
	void run() {cout << "A MotorCar is running!" << endl;}
	void stop() {cout << "A MotorCar has stopped!" << endl;}
};

class MotorCycle : public Bicycle, public MotorCar
{
private:
	int size;
public:
	MotorCycle() {}
	~MotorCycle() {}
	void run() {cout << "A MotorCycle is running!" << endl;}
	void stop() {cout << "A MotorCycle has stopped!" << endl;}
};

int main()
{
	Vehicle *ptr;
	Vehicle vehicle;
	Bicycle bicycle;
	MotorCar motocar;
	MotorCycle motocycle;
//看本身的对象,这种对run是不是虚基类没有差别
	//所以下面两行有没有都一样。
	vehicle = bicycle;  // 想想这样赋值是否正确，把这两条语句删除，看看结果有无变化 ————没有变化
	motocar = motocycle;
	vehicle.run(); //vehicle
	vehicle.stop(); //vehicle
	bicycle.run(); //bicycle
	bicycle.stop(); //bicycle
	motocar.run(); //motocar
	motocar.stop(); //motocar
	motocycle.run(); //motocycle
	motocycle.stop(); //motocycle
//指向基类的指针，可以指向子类，子类的指针不能指向基类
	//如果run不是虚基类，执行的是基类的run函数 
	//如果run是虚基类，执行的是指向的对象的run函数 
	ptr = &vehicle;
	ptr->run(); //vehicle
	ptr->stop();
	ptr = &bicycle;
	ptr->run(); //bicycle
	ptr->stop();
	ptr = &motocar;
	ptr->run(); //motocar
	ptr->stop();
	ptr = &motocycle;
	ptr->run(); //motocycle
	ptr->stop();

	

	return 0;
}

3 楼 vanillalyx 2009-05-14  

#include <iostream>
using namespace std;
void change(char **,char **);
//功能：互换两个指针的内容（即指针指向的地址）
int main()
{
	char* s1 = "Hello programmer, ";
	char* s2 = "welcome to C++ world!";

	cout <<s1 << endl;
	cout << s2 << endl;	
	change(&s1,&s2);

	cout<<"change after:"<<endl;
	cout <<s1 << endl;
	cout << s2 << endl;

	return 0;
}

void change(char **r1,char **r2)
{
	
	char *t ;	//一般人都写成 **t,其实我们要互换的只是s1和s2指向的字符串首地址,至于使用**t为什么在运行时出错，就不知道了。
	t = *r1; 
	*r1 = *r2;
	*r2 = t;

}

2 楼 vanillalyx 2009-04-23  

对浮点数比较大小时不要使用==  
  本来应该相等的两个浮点数由于计算机内部表示的原因可能略有微小的误差，这时用＝＝就会认为它们不等。应该使用两个浮点数之间的差异的绝对值小于某个可以接受的值来判断判断它们是否相等,比如用  
  if(fabs(fOldWidth-fNewWidth)<0.000001)  

1 楼 vanillalyx 2009-04-20  

#include <iostream>
#include <cstring>
using namespace std;
int main(){
float x;
int a=0,b=3;
switch (a+b)
{

case 2:x = (float)a/b;
default : x=a*b; //如果有匹配的（包括在这个语句下面的），不会执行这一句，否则执行

case 1+2 : x=3;  //有一个符合之后(包括default)，他后面的CASE后的语句全部执行，
case 5:x =5;


}
cout<<x;
return 0;
}