格式化输入 

#include <iostream>
#include<iomanip>
using namespace std;
 
int main()
{
    double num=1090.123456;
    cout<<"num="<<num<<endl;
    cout<<oct<<"num="<<num<<endl;
    cout<<hex<<"num="<<num<<endl;
    cout<<dec<<"num="<<num<<endl;
    cout<<"******************************"<<endl;
    cout<<setbase(8)<<"num="<<num<<endl;
    cout<<setbase(16)<<"num="<<num<<endl;
    cout<<setbase(10)<<"num="<<num<<endl;
    cout<<"******************************"<<endl;
    cout<<setw(10)<<"num="<<num<<endl;
    cout<<setw(10)<<setfill('*')<<"num = "<<num<<endl;
    return 0;
}

c++斐波那契

#include <iostream>

using namespace std;

int main()
{
    int num1=1;
    int num2=1;
    int sum=0;
    cout<<num1<<endl;
    cout<<num2<<endl;
    for(int i=0;i<18;i++)
    {
        sum=num1+num2;
        num1=num2;
        num2=sum;
        cout<<sum<<endl;
    }

    return 0;
}

大小写转换 

#include <iostream>

using namespace std;

int main()
{
    char word;
    cout<<"输入一个字符"<<endl;
    cin>>word;
    if(word>=65&&word<=90)
    {
        word=word+32;
        cout<<word<<endl;
    }
    else if(word>=97&&word<=122)
    {
        word=word-32;
        cout<<word<<endl;
    }
    else{
        cout<<"*"<<endl;
    }

    return 0;
}

自定义命名空间 

#include <iostream>

using namespace std;

namespace yh
{
    int num;
    double value;
    char key;
    void show()
    {
        cout<<"num="<<num<<"key="<<key<<"value="<<value<<endl;
    }
}
using yh::value;
int main()
{
    yh::num=666;
    value=3.14;
    using namespace yh;
    key='h';
    show();
    return 0;
}

 判断字符串数字，字母，空格，符号的数量

#include <iostream>

using namespace std;

int main()
{
    string str1;
    cout<<"输入字符串"<<endl;
    getline(cin,str1);
    int len=0,num=0,word1=0,word2=0,sign1=0,space1=0;
    len=str1.size();
    for(int a=0;a<len;a++)
    {
        if(str1[a]>='1'&&str1[a]<='9')
        {
            num++;
        }
        else if(str1[a]>='A'&&str1[a]<='Z')
        {
            word1++;
        }
        else if(str1[a]>='a'&&str1[a]<='z')
        {
            word2++;
        }
        else if(str1[a]==' ')
        {
            space1++;
        }
        else
        {
            sign1++;
        }
    }
    cout<<"数字"<<num<<"大写字母"<<word1<<"小写字母"<<word2<<"空格"<<space1<<"符号"<<sign1<<endl;
    return 0;
}