章3例题

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</pre><pre class="cpp" name="code">/*例3.1~3:无格式输入输出*/#include <iostream>using namespace std;int main(){int a,b,c=8;cout<<"请"<<"输"<<"入"<<"两个数"<<"\n";cin>>a>>b;cout<<a<<"\n"<<b<<"\n"<<c<<"\n";return 0;}

/*例3.5:进制转换*/#include <iostream>#include <iomanip>using namespace std;int main(){int a=7,b=8,c=17;cout<<a<<"\t\t"<<b<<"\t\t"<<c<<"\n";cout<<oct<<a<<"\t\t"<<b<<"\t\t"<<c<<"\n";cout<<hex<<a<<"\t\t"<<b<<"\t\t"<<c<<"\n";return 0;}

/*例3.4;字母大小写*/#include <iostream>#include <iomanip>using namespace std;int main(){int a=7,b=8,c=31;cout<<a<<"\t\t"<<b<<"\t\t"<<c<<"\n";cout<<hex<<a<<"\t\t"<<b<<"\t\t"<<c<<"\n";cout<<uppercase<<a<<"\t\t"<<b<<"\t\t"<<c<<"\n";cout<<nouppercase<<a<<"\t\t"<<b<<"\t\t"<<c<<"\n";return 0;}

/*例3.8：浮点数值显示：*/#include <iostream>#include <iomanip>using namespace std;int main(){double a=22.0/7;cout<<a<<endl;cout<<setprecision(0)<<a<<endl;cout<<setprecision(1)<<a<<endl;cout<<setprecision(4)<<a<<endl;    cout<<"-------------------------------"<<endl;cout<<fixed<<a<<endl;cout<<setprecision(0)<<a<<endl;cout<<setprecision(1)<<a<<endl;cout<<setprecision(4)<<a<<endl;    cout<<"-------------------------------"<<endl;cout<<scientific<<a<<endl;cout<<setprecision(0)<<a<<endl;cout<<setprecision(1)<<a<<endl;cout<<setprecision(4)<<a<<endl;return 0;}

/*例3.13：正整数逆转*/#include <iostream>using namespace std;int main(){int a,m,n;cout<<"请输入一个三位数:"<<endl;cin>>a;m=a/100;a%=100;n=a/10;a%=10;a=100*a+10*n+m;cout<<a<<endl;return 0;}

/*例3.14：复合语句*/#include <iostream>using namespace std;int main(){int x=10;cout<<x<<endl;{int x=20;cout<<x<<endl;{int x=30;cout<<x<<endl;}}cout<<x<<endl;return 0;}

复合语句逻辑先内后外，显示按字面顺序

/*例3.16:求方程a*x^2+b*x+c=0的根且满足b^2-4*a*c>0*/#include <iostream>#include<cmath>   //方程计算需加此头文件,开方sqrt()using namespace std;int main(){double a,b,c,x1,x2,disc,p,q;  //double类型而非intcout<<"请输入方程三个系数a,b,c:";cin>>a>>b>>c;disc=b*b-4*a*c;p=-b/(2*a);    q=sqrt(disc)/(2*a);x1=p+q;x2=p-q;cout<<x1<<"\t\t"<<x2<<endl;  //x=[-b+-sqrt(b^2-4ac)]/(2*a)return 0;}

/*例3.20:嵌套if语句*/#include <iostream>using namespace std;int main(){int x=6,y;if(x){if(x>0)y=1;elsey=-1;}elsey=0;cout<<y<<endl;return 0;}

/*switch 选择语句*/#include<iostream>using namespace std;int main(){int a;cout<<"请输入0-6任意一个数：";cin>>a;switch(a){case 0:cout<<"sunday"<<endl;break;  //满足比较条件后执行语句直至遇到breakcase 1:cout<<"monday"<<endl;break;case 2:cout<<"tuesday"<<endl;break;case 3:cout<<"wednesday"<<endl;break;case 4:cout<<"thursday"<<endl;break;case 5:cout<<"friday"<<endl;break;case 6:cout<<"saturday"<<endl;break;default:cout<<"error"<<endl;   //上面条件均不符合时执行此，若无此句则直接跳出}return 0;}

</pre><p></p><pre class="cpp" name="code">/*while语句求1+2+3+4+....+100*/#include<iostream>using namespace std;int main(){int a=0,b=0;while(a<100){a++;b+=a;}cout<<b<<endl;return 0;}

/*例3.24*/#include<iostream>using namespace std;int main(){int a,m=0,n=0;cout<<"请输入正整数：";cin>>a;while(a>0)  //以0输入结束循环{if(a>=60)m++;elsen++;cin>>a;}cout<<"大于等于60的个数："<<m<<endl;cout<<"小于60的个数："<<n<<endl;return 0;}

/*例3.25*/#include<iostream>using namespace std;int main(){int a,m=0,n=0;cout<<"请输入正整数：";cin>>a;do{if(a>=60)m++;elsen++;cin>>a;}while(a>0);cout<<"大于等于60的个数："<<m<<endl;cout<<"小于60的个数："<<n<<endl;return 0;}

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