第14周 《C++语言基础》程序阅读——标准输入输出对象及文本文件 （1）

1、阅读并运行下面的示例程序，掌握标准输入输出流的控制

例1

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include <iostream>
#include <math.h>
using namespace std;
int main()
{
    float a,b,c,disc;
    cout<<"please input a,b,c:";
    cin>>a>>b>>c;
    if (a==0)
        cerr<<"a is equal to zero,error!"<<endl;
    else if ((disc=b*b-4*a*c)<0)
        cerr<<"disc=b*b-4*a*c<0"<<endl;
    else
    {
        cout<<"x1="<<(-b+sqrt(disc))/(2*a)<<endl;
        cout<<"x2="<<(-b-sqrt(disc))/(2*a)<<endl;
    }
    return 0;
}
</span></strong>

例2

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
    int a;
    cout<<"input a:";
    cin>>a;
    cout<<"dec:"<<dec<<a<<endl;
    cout<<"hex:"<<hex<<a<<endl;
    cout<<"oct:"<<setbase(8)<<a<<endl;
    char *pt="China";
    cout<<setw(10)<<pt<<endl;
    cout<<setfill('*')<<setw(10)<<pt<<endl;
    double pi=22.0/7.0;
    cout<<setiosflags(ios::scientific)<<setprecision(8);
    cout<<"pi="<<pi<<endl;
    cout<<"pi="<<setprecision(4)<<pi<<endl;
    cout<<"pi="<<setiosflags(ios::fixed)<<pi<<endl;
    return 0;
}</span></strong>

例3

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include <iostream>
using namespace std;
int main()
{
    int a=21;
    cout.setf(ios::showbase);
    cout<<"dec:"<<a<<endl;
    cout.unsetf(ios::dec);
    cout.setf(ios::hex);
    cout<<"hex:"<<a<<endl;
    cout.unsetf(ios::hex);
    cout.setf(ios::oct);
    cout<<"oct:"<<a<<endl;
    char *pt="China";
    cout.width(10);
    cout<<pt<<endl;
    cout.width(10);
    cout.fill('*');
    cout<<pt<<endl;
    double pi=22.0/7.0;
    cout.setf(ios::scientific);
    cout<<"pi=";
    cout.width(14);
    cout<<pi<<endl;
    cout.unsetf(ios::scientific);
    cout.setf(ios::fixed);
    cout.width(12);
    cout.setf(ios::showpos);
    cout.setf(ios::internal);
    cout.precision(6);
    cout<<pi<<endl;
    return 0;
}</span></strong>

例4-1

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include <iostream>
using namespace std;
int main( )
{
    char *a="BASIC";		//字符指针指向'B'
    for(int i=4; i>=0; i--)
        cout.put(*(a+i));   //从最后一个字符开始输出
    cout.put('\n');
    return 0;
}
</span></strong>

例4-2

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include<iostream>
#include<cstdio>
int main()
{
    char *a="BASIC";
    for(int i=4; i>=0; i--)
        putchar(*(a+i));
    putchar('\n');
    return 0;
}</span></strong>

例5

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#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;
}
</span></strong>

例6

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include<iostream>
#include<cstdio>
using namespace std;
int main( )
{
    int c;
    cout<<"enter a sentence:"<<endl;
    while((c=cin.get())!=EOF)
        cout.put(c);
    return 0;
}
</span></strong>

(2) 有一个参数的get函数

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include<iostream>
#include<cstdio>
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;
}</span></strong>

(3) 有3个参数的get函数

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include<iostream>
using namespace std;
int main( )
{
    char ch[20];
    cout<<"enter a sentence:"<<endl;
    cin.get(ch,10,'\n');//指定换行符为终止字符
    cout<<ch<<endl;
    return 0;
}</span></strong>

例7

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#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;
}
</span></strong>