7

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

#include <iostream>#include <iomanip>using namespace std;int main(){float a[5]; cout<<"input data:"; for(int i=0;i<5;i++)  cin>>a[i]; cout<<setiosflags(ios::fixed)<<setprecision(2); for(i=0;i<5;i++)  cout<<setw(10)<<a[i]<<endl; return 0;}

#include <iostream>#include <iomanip>using namespace std;int main(){ for(int n=1;n<8;n++) cout<<setw(20-n)<<setfill(' ')<<" "        //nm<<setw(2*n-1)<<setfill('B')<<"B"<<endl; return 0;}

#include <iostream>#include <fstream>using namespace std;                //VC++ 6.0要此行//fun1函数从键盘输入20个整数，分别存放在两个磁盘文件中void fun1(){int a[10]; ofstream outfile1("f1.dat"),outfile2("f2.dat");  //分别定义两个文件流对象 if(!outfile1)                        //检查打开f1.dat是否成功  {cerr<<"open f1.dat error!"<<endl;   exit(1);  } if(!outfile2)                        //检查打开f2.dat是否成功  {cerr<<"open f2.dat error!"<<endl;   exit(1);  }  cout<<"enter 10 integer numbers:"<<endl; for(int i=0;i<10;i++)          //输入10个数存放到f1.dat文件中  {cin>>a[i];   outfile1<<a[i]<<" ";}  cout<<"enter 10 integer numbers:"<<endl; for(i=0;i<10;i++)           //输入10个数存放到f2.dat文件中  {cin>>a[i];   outfile2<<a[i]<<" ";} outfile1.close();               //关闭f1.dat文件 outfile2.close();               //关闭f2.dat文件}//从f1,dat读入10个数，然后存放到f2.dat文件原有数据的后面void fun2(){ifstream infile("f1.dat");       //f1.dat作为输入文件 if(!infile)  {cerr<<"open f1.dat error!"<<endl;   exit(1);  }  ofstream outfile("f2.dat",ios::app);  //f2.dat作为输出文件，文件指针指向文件尾，向它写入的数据放在原来数据的后面  if(!outfile)   {cerr<<"open f2.dat error!"<<endl;   exit(1);  }  int a;  for(int i=0;i<10;i++)   {infile>>a;           //磁盘文件f2.dat读入一个整数    outfile<<a<<" ";     //将该数存放到f2.dat中   }  infile.close();  outfile.close(); }//从f2.dat中读入20个整数，将它们按从小到大的顺序存放到f2.dat void fun3(){ifstream infile("f2.dat"); //定义输入文件流infile，以输入方式打开f2.dat  if(!infile)  {cerr<<"open f2.dat error!"<<endl;   exit(1);  } int a[20]; int i,j,t;for(i=0;i<20;i++)        infile>>a[i];        //从磁盘文件f2.dat读入20个数放在数组a中 for(i=0;i<19;i++)     //用起泡法对20个数排序   for(j=0;j<19-i;j++)      if(a[j]>a[j+1])        {t=a[j];a[j]=a[j+1];a[j+1]=t;}  infile.close();                //关闭输入文件f2.dat  ofstream outfile("f2.dat",ios::out);// f2.dat作为输出文件，文件中原有内容删除  if(!outfile)   {cerr<<"open f2.dat error!"<<endl;    exit(1);}cout<<"data in f2.dat:"<<endl;  for( i=0;i<20;i++)    {outfile<<a[i]<<" ";      //向f2.dat输出已排序的20个数     cout<<a[i]<<" ";}        //同时输出到显示器  cout<<endl;  outfile.close();}int main(){fun1();                     //分别调用3个函数 fun2(); fun3(); return 0;}

#include <iostream>#include <strstream>using namespace std;struct student{int num; char name[20]; 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 array stud1:"<<endl; for(i=0;i<3;i++)  cout<<stud1[i].num<<" "<<stud1[i].name<<" "<<stud1[i].score<<endl; cout<<endl; return 0;}