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
（1）不带参数的get函数

<strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">#include<iostream>#include<cstdio>using namespace std;int main( ){    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>