C++语言基础 例程 标准输入流

贺老师的教学链接  本课讲解

例: 输入个数不确定的成绩

#include <iostream>using namespace std;int main( ){    float grade;    cout<<"enter grade:";    while(cin>>grade)//能从cin流读取数据    {        if(grade>=85)            cout<<grade<<" GOOD!"<<endl;        if(grade<60)            cout<<grade<<" fail!"<<endl;        cout<<"enter grade:";    }    cout<<"The end."<<endl;    return 0;}

用于字符输入的流成员函数——get函数
（1）不带参数的get函数

#include <iostream>using namespace std;int main( ){    int c;    cout<<"enter a sentence:"<<endl;    while((c=cin.get())!=EOF)        cout.put(c);    return 0;}

(2) 有一个参数的get函数

#include <iostream>using namespace std;int main( ){    char c;    cout<<"enter a sentence:"<<endl;    while(cin.get(c))  //读取一个字符赋给字符变量c，如果读取成功，cin.get(c)为真        cout.put(c);    cout<<"end"<<endl;    return 0;}

(3) 有3个参数的get函数

#include <iostream>using namespace std;int main( ){    char ch[20];    cout<<"enter a sentence:"<<endl;    cin.get(ch,10,'/');//指定‘/’符号为终止字符    cout<<ch<<endl;    return 0;}

用于输入一行字符的流成员函数——getline函数

#include <iostream>using namespace std;int main( ){    char ch[20];    cout<<"enter a sentence:"<<endl;    cin>>ch;    cout<<"The string read with cin is:"<<ch<<endl;    cin.getline(ch,20,'/');//读19个字符或遇'/'结束    cout<<"The second part is:"<<ch<<endl;    cin.getline(ch,20);                              //读19个字符或遇'/n'结束    cout<<"The third part is:"<<ch<<endl;    return 0;}

判断输入(文件)是否结束——eof函数

#include <iostream>using namespace std;int main( ){    char c;    while(!cin.eof( )) //eof( )为假表示未遇到文件结束符        if((c=cin.get( ))!=' ')//检查读入的字符是否为空格字符            cout.put(c);    return 0;}

输入流其他函数——

#include <iostream>using namespace std;int main( ){    char c[20];    int ch;    cout<<"please enter a sentence:"<<endl;    cin.getline(c,15,'/');    cout<<"The first part is:"<<c<<endl;    ch=cin.peek( );         //取当前字符    cout<<"next character: "<<char(ch)<<endl;    cin.putback(c[0]);   //插入c[0]    cin.getline(c,15,'/');    cout<<"The second part is:"<<c<<endl;    return 0;}