#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
int a[30];
double tot = 0 , b[30];
int main()
{
a[0] = 1, a[1] = 2;
for(int i = 2; i < 25; i++)
a[i] = a[i-1] + a[i-2];
for(int i = 1; i <= 20; i++)
{
b[i] = 1.0*a[i]/a[i-1];
tot += b[i];
}
printf("%.5lf\n", tot);
return 0;
}

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
int gcd(int x, int y)
{
if(x < y) return gcd(y,x);
if(y == 0) return x;
return gcd(y, x % y);
}
class Fraction
{
private:
int fz; //分子
int fm; //分母
public:
Fraction(){}
Fraction(const Fraction &p){
fz = p.fz;
fm = p.fm;
}
Fraction(int x, int y)
{
fz = x;
fm = y;
}
void show()
{
cout<<fz<<'/'<<fm<<endl;
}
void operator += (Fraction &p)
{
Fraction t;
t.fz = fz*p.fm + p.fz*fm;
t.fm = fm*p.fm;
fz = t.fz;
fm = t.fm;
int temp = gcd(fz, fm);
fz /= temp;
fm /= temp;
}
friend ostream &operator << (ostream &, Fraction &);
};
ostream & operator << (ostream &os, Fraction &p)
{
os<<p.fz<<'/'<<p.fm<<endl;
return os;
}
int main()
{
Fraction a(3,4), b(6,9);
a+=b;
Fraction c(a);
cout<<c;
return 0;
}

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
class Student {
private:
char name[10];
char num[10];
public:
Student() {}
Student(char a[], char b[])
{
strcpy(name, a);
strcpy(num, b);
}
void show()
{
cout<<name<<endl;
cout<<num<<endl;
}
};
class SStack {
private:
Student * d;
Student * top;
int size, used;
public:
SStack() {
size = 1;
d = new Student[size];
top = d;
used = 0;
}
SStack(int s) {
size = s;
d = new Student[size];
top = d;
used = 0;
}
void full()
{
Student * nd;
Student * t = d;
Student * ntop;
size = size * 2;
nd = new Student[size];
ntop = nd;
for(int i = 0; i < used; i++)
{
*ntop = *t;
ntop++;
t++;
}
delete [] d;
d = nd;
top = ntop;
}
void Push(Student s1)
{
if(used >= size)
full();
*top = s1;
top++;
used++;
}
Student Pop()
{
if(used == 0)
{
cout<<"error：栈空"<<endl;
}
else {
used--;
top--;
return *top;
}
}
};
int main()
{
char name[] = {'W', 'X', 'C', '\0'};
char num[] = {'1', '3', '5', '\0'};
Student s(name, num);
SStack a;
a.Pop();
a.Push(s);
a.Push(s);
a.Push(s);
a.Push(s);
for(int i = 1; i < 6; i++)
{
s = a.Pop();
}
return 0;
}

#include <iostream>
#include <cstdio>
#include <cstring>
#define PI 3.1415926
using namespace std;
class Shape {
public:
Shape() {}
virtual double show() = 0;
double ShowTotalArea(Shape *s[],int n)
{
double temp = 0;
for(int i = 0; i < n; i++)
temp += s[i]->show();
return temp;
}
};
class Circle : public Shape {
public:
Circle(float Radius) {
mRadius = Radius;
}
double show() {
return PI*mRadius*mRadius;
}
private:
float mRadius;
};
class Rectangle : public Shape {
public:
Rectangle(float Length, float Height) {
mLength = Length;
mHeight = Height;
}
double show() {
return mLength*mHeight;
}
private:
float mLength, mHeight;
};
int main()
{
Circle c(2.0);
Rectangle r(2.0, 3.0);
Shape *p[2] = {&c, &r};
cout<<p[0]->show()<<endl;
cout<<p[1]->show()<<endl;
Shape *p1;
cout<<p1->ShowTotalArea(p, 2)<<endl;
return 0;
}