C ++ string, vector

String and vector are two standard library types. The former supports variable-length strings, and the latter supports variable-length collections. Built-in arrays are more basic types, and string and vector are some abstractions of it.

1. string

Call the string library:

#include <string>
using std::string

Five forms defined by string:

#include <iostream>
#include <string>
using namespace std;
int main(){
	string s1 = "Hello";//拷贝初始化
	string s1_copy = s1;//拷贝
	string s2(5,'a');//直接初始化
	string s2_copy(s2);//拷贝
	string s3("Hello world!");//直接初始化
	
	cout << s1 << endl;
	cout << s1_copy << endl;
	cout << s2 << endl;
	cout << s2_copy<< endl;
	cout << s3 << endl;
} 

result:

Hello
Hello
aaaaa
aaaaa
Hello world!

string operation

operating	meaning
getline(is,s)	Read a line from is and assign it to s
s.empty()	true if s is empty, false otherwise
s.size()	s characters
s[n]	Character with index n
s1 + s2	The result of connecting s1 and s2
s1 == s2	Determine if they are equal
s1! = s2	Determine if they are not equal
<,<=,>,>=	Lexicographical comparison

Read and write string objects :

When reading, string automatically ignores the leading white space (space character, new line character, tab character, etc.), starting from the real character until it encounters the next white space.

#include <iostream>
#include <string>
using namespace std;
int main(){
	string s1;
	cin >> s1; 
	cout << s1 << endl;
} 

result:

Hello world
Hello

Reading an unknown number of string objects The
input stream has been reading.

#include <iostream>
#include <string>
using namespace std;
int main(){
	string word;
	while(cin >> word){
		cout << word << endl;
	}
} 

result:

Hello world we are champion// 输入
Hello
world
we
are
champion

Use getline to read an entire line
so that the space character can be read.

#include <iostream>
#include <string>
using namespace std;
int main(){
	string line;
	while(getline(cin,line)){
		cout << line << endl;
	}
	return 0;
} 

endlEnd the current line and refresh the display buffer.
result:

we are champion//输入
we are champion
are you ok//输出
are you ok

2. vector

Vector represents a collection of objects, and vector is also called a container.

#include <vector>
using std::vector;

Vector 5 initialization methods:

#include <iostream>
#include <vector>

using namespace std;
void print_vector(vector<auto> vec){
	for (auto i:vec){
		cout << i << " ";
	}	
	cout << endl;
}
int main(){
	vector<int> v1(5,10);//5个重复元素，值为10
	vector<int> v1_copy(v1);
	vector<int> v2{1,2,3,4,5};
	vector<int> v2_copy = v2;
	vector<int> v3={1,2,3,4,5};

	print_vector(v1);
	print_vector(v1_copy);
	print_vector(v2);
	print_vector(v2_copy);
	print_vector(v3);
} 

result:

10 10 10 10 10
10 10 10 10 10
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5

If you simply declare the definition vector<T> vec, it is initialized by default and veccontains no elements.

If you can't compile, you need to set the compiler's compilation standard to ISO C++11.Dev C ++ 's Tools-Compiler Options-Code Generation-Language Standard.

If you traverse the process, you want to vectorchange the value of:

for(auto &v : vec){
	v *= v;
}

vector operation

operating	meaning
push_back()	Add element
v.empty()	Determine if it contains elements
v.size()	Number of elements
v [n]	Take the value at index n
v1 = v2	Replace elements of v1 with elements from v2 (same container type)
v1 == v2	Determine if they are equal
v1 != v2	Determine if they are not equal
<,<=,>,>=	Lexicographical comparison

Vector access:

#include <iostream>
#include <vector>

using namespace std;

void print_vector(vector<auto> vec){
	for (auto i:vec){
		cout << i << " ";
	}	
	cout << endl;
}
int main(){
	vector<float> v{1,2,3,4,5};
	for (auto &i : v){// i是一个引用
		i *= i;
	}
	print_vector(v);
} 

3. Array

The size of the array is fixed.

Array initialization:

#include <iostream>
using namespace std;

int main(){
	int a[5] = {0,1,2};
	string s[5] = {"hi","world"};
	for(auto i:a){
		cout<< i<< endl;
	}
} 

result:

0
1
2
0
0

Pointers and arrays:

#include <iostream>
using namespace std;

int main(){
	int arr[5] = {0,1,2};
	int *ip = arr;// 等价于int *p = &arr[0]
	int *ip2 = ip+2;//ip2指向arr[2]
	cout << *ip << endl;
	cout << *ip2 << endl;
} 

result:

0
2

Multidimensional Arrays:

#include <iostream>
using namespace std;

int main(){
	int arr[2][3] = {
	{0,1,2},
	{3,4,5},
	};
	for (auto &row : arr){
		for (auto &col : row){
			cout << col << endl;
		}
	}
} 

result:

0
1
2
3
4
5