Introduction to c++

时间：2024-10-09 15:09:49

1. keywords

The first one  is to introduce the keywords

here is a  picture for everyone

 2.namespace

The second is namespace, to prevent conflicts between variables, functions, and classes in the global domain
Let's take an example 

Compile-time error, because there was  a problem with a redefinition

2.namespace

Usually, we define a namespace by our names, and it can be nested, the same project can be named the same, and eventually be merged.

 its useage

1. assign namespace names and operation qualifiers

int main()
{
	printf("%d", N1::a);
	return 0;
}

2. using the "using" keywords to reference a namespace

using N1::b;
int main()
{
	printf("%d", b);
	return 0;
}

3. using "using namespace "keywords to reference, this is commonly used

using namespace N1;
int main()
{
	printf("%d", b);
	return 0;
}

3.cin & cout

Take a example

#include<iostream>
using namespace std;

int main()
{
	cout << "Hello world!!!" << endl;
	return 0;
}

4.The differneces  in  header files 

The difference between c and C++ header  files, to distinguish c and C++,general c++files not .h

5.std

The usage convention of std:  it can be used in daily life, but it is not recommended for work
because it would expose the entire standard library

6.Default parameters

There are two types. The first is full default parameters, and the second is semi-default parameters
there are four points to knowone of them is that semi-default must be given in order from right to left, and another is that default parameter can't appear simultaneously in the declaration and definition, the third is default values must be constants or local variables, the last one is that c language doesn't support

7.Function  overloading

due to the allowance in C++ for declaring several functionally  similar functions with the same domain, but requiring different parameter lists

8.Quote(引用)

Quote doesn't create a new variable, it just takes another alian, all share a sigle space.
This is  an example

#include<iostream>
using namespace std;
void TestRef()
{
	int a = 10;
	int& ra = a;
	cout << a << endl;
	cout << ra << endl;
}
int main()
{
	TestRef();
	return 0;
}

cited characteristic 

1. initializations must occur when defining.
2. a variable can have multiple references.
3. a quotation can quatity one thing

This is an example 

#include<iostream>
using namespace std;
void TestRef()
{
	const int a = 10;
	const int& b = a;
	cout << a;
	cout << b;
}
int main()
{
	TestRef();
	return 0;
}

9.Function(作用)


1. do the parameters
2. make a return value


10. Efficiency


The citation is the most efficient

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