#include <iostream>
using namespace std;int main()
{bool a = false;int b = 5;float c = 0.01;char *d = NULL;if (a){cout<<"a = 1"<<endl;}else//(!a){cout<<"a = 0"<<endl;}if (b == 0){cout<<"b = 0"<<endl;}else{cout<<"b != 0"<<endl;}if ((c > -0.000001) && (c < 0.000001)){cout<<"c = 0"<<endl;}else if (c < -0.000001){cout<<"c < 0"<<endl;}else{cout<<"c > 0"<<endl;}if (NULL == d){cout<<"d = NULL"<<endl;}else{cout<<"d != NULL"<<endl;}return 0;
}

3.c中的struct结构体与c++中的class类和对象

#include <iostream>using namespace std;struct student{char *name;int age;float score;
};int main()
{struct student stu1;stu1.name = "xiaoming";stu1.age = 19;stu1.score = 59.8;printf("%s %d %6.3f\n", stu1.name, stu1.age, stu1.score);return 0;
}

显然c++的类和对象更方便，功能也更强大。但是要记牢class的用法，和特点

#include <iostream>using namespace std;class student{
public :char name[24];//char *name;int age;float score;void say(){printf("name:%s\nage:%d\nscore:%6.3f\n", name, age, score);//cout<<"name = "<<name<<"\nage = "<<age<<"\nscore = "<<score<<endl;}
};int main()
{class student stu1;strcpy(stu1.name, "xiaoming");stu1.age = 19;stu1.score = 59.8;stu1.say();return 0;
}

4.在堆上申请空间和释放new和delete

int *p;
p = new int;

char *pstr = new char [50];

delete可以用于释放堆上的空间，语法如下：

delete p;
delete [50] pstr;

5.命名空间

#include <iostream>using namespace std;namespace nsa{void print(){cout<<"nsa"<<endl;}
}namespace nsb{void print(){cout<<"nsb"<<endl;}
}int main()
{nsa::print();nsb::print();return 0;
}

（1）using 声明

#include <iostream>using std :: cin;//using声明，表明要引用标准库std中的成员cin；
using std :: string;//using声明，表明要引用标准库std中的成员string；
using std :: endl;int main()
{string temp;cin>>temp;std :: cout<<temp<<endl;return 0;
}

（2）using的作用域

#include <iostream>using namespace std;namespace nsa{int a = 5;
}namespace nsb{float a = 5.55;
}int main()
{{using namespace nsa;cout<<"nsa a = "<<a<<endl;//using指令，使用nsa}{using namespace nsb;cout<<"nsb a = "<<a<<endl;//using指令，使用nsb}return 0;
}

6.函数的重载

#include <iostream>
using namespace std;int max(int a, int b);
int max(int a, int b, int c);
double max(double a, double b);int main()
{int n;int a = 2;int b = 3;int c = 5;double z;double x = 55.5;double y = 66.6;n = max(a, b);cout<<"a = "<<a<<" b = "<<b<<" max = "<<n<<endl;z = max(x, y);cout<<"x = "<<x<<" y = "<<y<<" max = "<<z<<endl;n = max(a, b, c);cout<<"a = "<<a<<" b = "<<b<<" c = "<<c<<" max = "<<n<<endl;return 0;
}int max(int a, int b)
{return a > b ? a : b;
}int max(int a, int b, int c)
{int temp;temp = a > b ? a : b;return temp > c ? temp : c;
}double max(double a, double b)
{return a > b ? a : b;
}

void func(int a, double b = 5.5, int c = 3);//合法
void func1(int a = 1, double b = 5.5, int c = 3);//不合法

#include <iostream>
using namespace std;void func(int x, int y = 0, int z = 0)
{cout<<x<<","<<y<<","<<z<<endl;
}int main()
{int x, y, z;cout<<"x,y,z:"<<endl;cin>>x>>y>>z;func(x);func(x, y);func(x, y, z);return 0;
}

#include <iostream>
using namespace std;inline int max(int a, int b);int main()
{int a[10];cout<<"please input 10 numbers :\n"<<endl;int i;for (i = 0; i < 10; i++){cin>>a[i];}int temp = a[0];for (i = 0; i < 10; i++){temp = max(temp, a[i]);}cout<<"the max number of the 10 numbers is "<<temp<<endl;return 0;
}inline int max(int a, int b)
{return a > b ? a : b;
}