C++第七章

1.#include <iostream>
#include <cmath>
using namespace std;
void area(float a,float b,float c)
{
 double s,area;
 if(a+b<=c)
	 cerr<<"a+b<=c,error!"<<endl;
 else if(b+c<=a)
	 cerr<<"b+c<=a,error!"<<endl;
 else if(a+c<=b)
	 cerr<<"a+c<=b,error!"<<endl;
 else
 {
  s=(a+b+c)/2;
  area=sqrt(s*(s-a)*(s-b)*(s-c));
  cout<<"area="<<area<<endl;
 }
}
int main()
{
 float a=2,b=3,c=4;
 area(a,b,c);
 return 0;
}

2. #include <iostream>
using namespace std;
int main()
{
 float a[5];
 int i;
 cout<<"input number:";
 for(i=0;i<5;i++)
	 cin>>a[i];
 cout.setf(ios::fixed);
 cout.precision(3);
 for(i=0;i<5;i++)
 {
  //cout.width(10);
  cout<<a[i]<<endl;
 }
 return 0;
}

3. #include <iostream>
#include <iomanip>
using namespace std;
int main()
{
 for(int i=1;i<8;i++)
	 cout<<setw(20-i)<<setfill(' ')<<" "<<setw(2*i-1)<<setfill('B')<<"B"<<endl;  //设置填充字符
 return 0;
}

4. #include <iostream>
#include <fstream>
using namespace std;
void fun1()
{
 int a[10];
 ofstream outfile1("f1.data",ios::out),outfile2("f2.data",ios::out);
 if(!outfile1)
 {
  cerr<<"open error!"<<endl;
  exit(1);
 }
 if(!outfile2)
 {
  cerr<<"open error!"<<endl;
  exit(1);
 }
 cout<<"input 10 integer numbers:"<<endl;
 for(int i=0;i<10;i++)
 {
  cin>>a[i];
  outfile1<<a[i]<<" ";
 }
 cout<<"input 10 integer numbers:"<<endl;
 for(i=0;i<10;i++)
 {
  cin>>a[i];
  outfile2<<a[i]<<" ";
 }
 outfile1.close();
 outfile2.close();
}
void fun2()
{
 ifstream infile("f1.data");
 if(!infile)
 {
	cerr<<"open error!"<<endl;
    exit(1);
 }
 ofstream outfile("f2.data",ios::app);
 if(!outfile)
 {
    cerr<<"open error!"<<endl;
	exit(1);
 }
 int a;
 for(int i=0;i<10;i++)
 {
  infile>>a;
  outfile<<a<<" ";
 }
 infile.close();
 outfile.close();
}
void fun3()
{
 ifstream infile("f2.data");
 if(!infile)
 {
  cerr<<"open error!"<<endl;
  exit(1);
 }
 int a[20];
 int i,j,t;
 for(i=0;i<20;i++)
	 infile>>a[i];
 for(i=0;i<20;i++)
	 for(j=i+1;j<20;j++)
		 if(a[i]>a[j])
		 {t=a[i];a[i]=a[j];a[j]=t;}
 infile.close();
 ofstream outfile("f2.data",ios::out);
 if(!outfile)
 {
   cerr<<"open error!"<<endl;
	   exit(1);
 }
 cout<<"data in f2.data:"<<endl;
 for(i=0;i<20;i++)
 {
  outfile<<a[i]<<" ";
  cout<<a[i]<<" ";
 }
 cout<<endl;
 outfile.close();
}
int main()
{
 fun1();
 fun2();
 fun3();
 return 0;
}

5. #include <iostream>
#include <fstream>
using namespace std;
struct staff
{
 int num;
 char name[10];
 int age;
 double pay;
};
int main()
{
	staff s[7]={1,"xiong",18,10000,3,"xian",18,20000,2,"piao",26,20000,4,"xin",26,10000,5,"xun",20,15000},s1;
    fstream iofile("staff.dat",ios::in|ios::out|ios::binary);
    if(!iofile)
	{
	 cerr<<"open error!"<<endl;
	 abort();
	}
	int i,m,num;
	cout<<"Five staff:"<<endl;
	for(i=0;i<5;i++)
	{
	 cout<<s[i].num<<" "<<s[i].name<<" "<<s[i].age<<" "<<s[i].pay<<endl;
	 iofile.write((char *)&s[i],sizeof(s[i]));
	}
	cout<<"Please insert two staff's message:"<<endl;
	for(i=0;i<2;i++)
	{cin>>s1.num>>s1.name>>s1.age>>s1.pay;
	iofile.seekp(0,ios::end);
	iofile.write((char *)&s1,sizeof(s1));}
	iofile.seekg(0,ios::beg);
	for(i=0;i<7;i++)
	{iofile.read((char *)&s[i],sizeof(s[i]));
	cout<<s[i].num<<" "<<s[i].name<<" "<<s[i].age<<" "<<s[i].pay<<endl;}
	bool find;
	cout<<"enter number you want to search,enter 0 to stop";
	cin>>num;
	while(num)
	{
	 find=false;
	 iofile.seekg(0,ios::beg);
	 for(i=0;i<7;i++)
	 {
	  iofile.read((char *)&s[i],sizeof(s[i]));
	  if(num==s[i].num)
	  {
	   m=iofile.tellg();
	   cout<<num<<"is NO."<<m/sizeof(s1)<<endl;
	   cout<<s[i].num<<" "<<s[i].name<<" "<<s[i].age<<" "<<s[i].pay<<endl;
	   find=true;
	   break;
	  }
	 }
	 if(!find)
		 cout<<"can't find!"<<num<<endl;
	 cout<<"please input again!";
	 cin>>num;
	}
	iofile.close();
	return 0;
}

6. #include <iostream>
#include <strstream>
using namespace std;
//struct staff
struct student
{
 int num;
 char name[10];
 //int age;
 //double pay;
 double score;
};
int main()
{
	student stud[3]={1001,"Li",78,1002,"Wang",89.5,1004,"Fun",90},stud1[3];
    char c[50];
	int i;
	ostrstream strout(c,50);
	for(i=0;i<3;i++)
		strout<<stud[i].num<<" "<<stud[i].name<<" "<<stud[i].score<<" ";
	strout<<ends;
	cout<<"array c:"<<endl<<c<<endl<<endl;
	istrstream strin(c,50);
	for(i=0;i<3;i++)
		strin>>stud1[i].num>>stud1[i].name>>stud1[i].score;
	cout<<"data from array c to arry s1:"<<endl;
	for(i=0;i<3;i++)
		cout<<stud[i].num<<" "<<stud[i].name<<" "<<stud[i].score<<endl;
	cout<<endl;
	return 0;
}